SFD IS 800 2007

User Manual: SFD-IS-800-2007

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Steel Frame Design Manual

IS 800:2007

Steel Frame

Design Manual

IS 800:2007

For ETABS® 2016

ISO ETA122815M14 Rev. 0

Proudly developed in the United States of America December 2015

The CSI Logo®, SAP2000®, ETABS®, and SAFE® are registered trademarks of

Computers & Structures, Inc. Watch & LearnTM is a trademark of Computers &

Structures, Inc.

The computer programs SAP2000® and ETABS® and all associated documentation are

proprietary and copyrighted products. Worldwide rights of ownership rest with

Computers & Structures, Inc. Unlicensed use of these programs or reproduction of

documentation in any form, without prior written authorization from Computers &

Structures, Inc., is explicitly prohibited.

No part of this publication may be reproduced or distributed in any form or by any

means, or stored in a database or retrieval system, without the prior explicit written

permission of the publisher.

Further information and copies of this documentation may be obtained from:

Computers & Structures, Inc.

www.csiamerica.com

info@csiamerica.com (for general information)

support@csiamerica.com (for technical support)

DISCLAIMER

CONSIDERABLE TIME, EFFORT AND EXPENSE HAVE GONE INTO THE

DEVELOPMENT AND TESTING OF THIS SOFTWARE. HOWEVER, THE USER

ACCEPTS AND UNDERSTANDS THAT NO WARRANTY IS EXPRESSED OR

IMPLIED BY THE DEVELOPERS OR THE DISTRIBUTORS ON THE ACCURACY

OR THE RELIABILITY OF THIS PRODUCT.

THIS PRODUCT IS A PRACTICAL AND POWERFUL TOOL FOR STRUCTURAL

DESIGN. HOWEVER, THE USER MUST EXPLICITLY UNDERSTAND THE BASIC

ASSUMPTIONS OF THE SOFTWARE MODELING, ANALYSIS, AND DESIGN

ALGORITHMS AND COMPENSATE FOR THE ASPECTS THAT ARE NOT

ADDRESSED.

THE INFORMATION PRODUCED BY THE SOFTWARE MUST BE CHECKED BY

A QUALIFIED AND EXPERIENCED ENGINEER. THE ENGINEER MUST

INDEPENDENTLY VERIFY THE RESULTS AND TAKE PROFESSIONAL

RESPONSIBILITY FOR THE INFORMATION THAT IS USED.

Contents

1 Introduction

1.1 Organization 1-2

1.2 Recommended Reading/Practice 1-3

2 Modeling, Analysis and Design Prerequisites

2.1 Check and Design Capability 2-1

2.2 Analysis Sections vs. Design Sections 2-2

2.3 Design and Check Stations 2-3

2.4 Demand/Capacity Ratios 2-3

2.5 Design Load Combinations 2-4

2.6 Second Order P-Delta Effects 2-6

2.7 Notional Load Cases 2-8

Contents - i

Steel Frame Design IS 800:2007

2.8 Member Unsupported Lengths 2-9

2.9 Effective Length Factor (K) 2-11

2.10 Effects of Breaking a Member into Multiple Elements 2-14

2.11 Supported Framing Types 2-16

2.12 Continuity Plates 2-16

2.13 Doubler Plates 2-18

2.14 Frame Design Procedure Overwrites 2-19

2.15 Interactive Design 2-19

2.16 Automated Iterative Design 2-20

2.17 Choice of Units 2-20

3 Design using IS 800:2007

3.1 Notations 3-2

3.2 Design Preferences 3-5

3.3 Overwrites 3-7

3.4 Design Loading Combinations 3-12

3.5 Design Strength 3-13

3.6 Classification of Sections for Local Buckling 3-13

3.7 Calculation of Factored Forces and Moments 3-20

ii - Contents

Contents

3.8 Calculation of Factored Strengths 3-21

3.8.1 Design Tensile Strength 3-21

3.8.2 Design Compressive Strength 3-22

3.8.3 Flexure Strength 3-28

3.8.4 Design Shear Strength 3-32

3.9 Design of Members for Combined Forces 3-35

3.9.1 Combined Axial and Bending Moment 3-35

3.9.2 Combined Axial Force, Bending Moment, and Shear

Force 3-44

3.9.3 Shear Stresses 3-44

3.10 Checking the Maximum Effective Slenderness Ratio of a

Member 3-45

4 Special Seismic Provisions

4.1 Design Preferences 4-1

4.2 Overwrites 4-2

4.3 Supported Framing Types 4-2

4.4 Design Special Load Combinations 4-3

4.5 Special Check for Column Strength 4-3

4.6 Member Design 4-4

4.6.1 Ordinary Concentrically Braced Frames (OCBF) 4-4

4.6.2 Special Concentrically Braced Frames (SCBF) 4-5

4.6.3 Eccentrically Braced Frames (EBF) 4-6

4.6.4 Ordinary Moment Frames (OMF) 4-6

4.6.5 Special Moment Frames (SMF) 4-6

4.6.6 Secondary (Non-Seismic) 4-7

4.7 Joint Design 4-7

4.7.1 Design of Continuity Plates 4-7

Contents - iii

Steel Frame Design IS 800:2007

4.7.2 Design of Doubler Plates 4-8

4.7.3 Weak Beam/Strong Beam Measure 4-11

4.7.4 Evaluation of Beam Connection Shears 4-14

4.7.5 Evaluation of Brace Connection Forces 4-15

5 Design Output

5.1 Graphical Display of Design Information 5-2

5.2 Tabular Display of Design Information 5-5

5.3 Detailed Display of Member Specific Information 5-8

5.4 Save or Print Design Information as Tables 5-13

5.5 Error and Warning Messages 5-15

Bibliography

iv - Contents

Chapter 1

Introduction

The design/check of steel frames is seamlessly integrated within the program.

Automated design at the object level is available for any one of a number of

user-selected design codes, as long as the structures have first been modeled

and analyzed by the program. Model and analysis data, such as material prop-

erties and member forces, are recovered directly from the model database, and

no additional user input is required if the design defaults are acceptable.

The design is based on a set of user-specified loading combinations. However,

the program provides default load combinations for each supported design

code. If the default load combinations are acceptable, no definition of addition-

al load combinations is required.

Steel frame design/check consists of calculating the flexural, axial, and shear

forces or stresses at several locations along the length of a member, and then

comparing those calculated values with acceptable limits. That comparison

produces a demand/capacity ratio, which typically should not exceed a value of

one if code requirements are to be satisfied. The program follows the same re-

view procedures when it is checking a user-specified shape or when checking a

shape selected by the program from a predefined list.

The program also checks the requirements for the beam-column capacity ratio,

checks the capacity of the panel zone, and calculates the doubler plate and con-

1 - 1

Steel Frame Design IS 800:2007

tinuity plate thickness, if needed. The program does not do the connection de-

sign. However, it calculates the design basis forces for connection design.

Program output can be presented graphically on the model, in tables for both

input and output data, or in calculation sheets prepared for each member. For

each presentation method, the output is in a format that allows the engineer to

quickly study the stress conditions that exist in the structure, and in the event

the member is not adequate, aid the engineer in taking appropriate remedial

measures, including altering the design member without re-running the entire

analysis.

The program supports a wide range of steel frame design codes, including

many national building codes. This manual is dedicated to the use of the menu

option "Indian IS 800:2007." This option covers the “Indian Standard – Gen-

eral Construction in Steel – Code of Practice, Third Revision” (IS 2007).

The design codes supported under “Indian IS 800:2007” are written in Newton-

millimeter units. All the associated equations and requirements have been im-

plemented in the program in Newton-millimeter units. The program has been

enabled with unit conversion capability. This allows the users to enjoy the flex-

ibility of choosing any set of consistent units during creating and editing mod-

els, exporting and importing the model components, and reviewing the design

results.

1.1 Organization

This manual is designed to help you quickly become productive using the

“Indian IS 800:2007” steel frame design option. Chapter 2 addresses

prerequisites related to modeling and analysis for a successful design in

accordance with IS 800:2007. Chapter 3 provides detailed descriptions of the

specific requirements as implemented in “Indian IS 800:2007.” Chapter 4

provides detailed descriptions of the specific requirements for seismic loading

as required by the specification IS 800:2007.

1 - 2 Organization

Chapter 1 - Introduction

1.2 Recommended Reading/Practice

It is strongly recommended that you read this manual and review any applica-

ble "Watch & Learn" SeriesTM tutorials, which are found on our web site,

http://www.csiamerica.com, before attempting to design a steel frame. Addi-

tional information can be found in the on-line Help facility available from

within the program.

Recommended Reading/Practice 1 - 3

Chapter 2

Modeling, Analysis and Design Prerequisites

This chapter provides an overview of the basic assumptions, design precondi-

tions, and some of the design parameters that affect the design of steel frames.

For referring to pertinent sections of the corresponding code, a unique prefix is

assigned for each code.

• Reference to the IS 800:2007 code is identified with the prefix "IS."

• Reference to the IS 1893 (Part 1):2002 code is identified with the prefix

"IS 1893."

2.1 Check and Design Capability

The program has the ability to check adequacy of a section (shape) in accord-

ance with the requirements of the selected design code. Also the program can

automatically choose (i.e., design) the optimal (i.e., least weight) sections from

a predefined list that satisfies the design requirements.

To check adequacy of a section, the program checks the demand/capacity

("D/C") ratios at a predefined number of stations for each design load combina-

tion. It calculates the envelope of the D/C ratios. It also checks the other re-

quirements on a pass or fail basis. If the capacity ratio remains less than or

equal to the D/C ratio limit, which is a number close to 1.0, and if the section

passes all the special requirements, the section is considered to be adequate;

2 - 1

Steel Frame Design IS 800:2007

otherwise the section is considered to have failed. The D/C ratio limit is taken

as 0.95 by default. However, this value can be overwritten in the Preferences

(Chapter 3).

To choose (design) the optional section from a predefined list, the program first

orders the list of sections in increasing order of weight per unit length. Then it

starts checking each section from the ordered list, starting with the one with the

least weight. The procedure for checking each section in this list for adequacy

is exactly the same as described in the preceding paragraph. The program will

evaluate each section in the list until it finds the least weight section that passes

the code checks. If no section in the list is acceptable, the program will use the

heaviest section but flag it as being overstressed.

To check adequacy of an individual section, the user must assign the section

using the Assign menu. In that case, both the analysis and design sections will

be changed.

To choose the optimal section, the user must first define a list of steel sections,

the Auto Select sections list. The user must next assign this list, in the same

manner as any other section assignment, to the frame members to be opti-

mized. The program will use the median section by weight when doing the ini-

tial analysis. Refer to the program Help for more information about Auto Se-

lect section lists.

2.2 Analysis Sections vs. Design Sections

Analysis sections are those section properties used to analyze the model when

an analysis is run. The design section is whatever section is used in the steel

frame design. It is possible for the last used analysis section and the current de-

sign section to be different. For example, an analysis may be run using a

W18X35 beam, and then in the design, it may be found that a W16X31 beam

worked. In that case, the last used analysis section is the W18X35 and the cur-

rent design section is the W16X31. Before the design process is complete, veri-

fy that the last used analysis section and the current design section are the

same. Refer to the program Help for more information about completing this

task.

The program keeps track of the analysis section and the design section sepa-

rately. Note the following about analysis and design sections:

2 - 2 Analysis Sections vs. Design Sections

Chapter 2 Design Algorithms

 Assigning a frame section property assigns the section as both the analysis

section and the design section.

 Running an analysis always sets the analysis section to be the same as the

current design section.

 Assigning an Auto Select section list to a frame object initially sets the

analysis and design section to be the section in the list with the median

weight.

 Unlocking a model deletes the design results, but it does not delete or

change the design section.

 Altering the Design Combinations in any way deletes the design results,

but does not delete or change the design section.

 Altering any of the steel frame design preferences deletes the design re-

sults, but does not delete or change the design section.

2.3 Design and Check Stations

For each design combination, steel frame members (beams, columns, and brac-

es) are designed (optimized) or checked at a number of locations (stations)

along the length of the object. The stations are located at equally spaced seg-

ments along the clear length of the object. By default, at least three stations

will be located in a column or brace member, and the stations in a beam will be

spaced at most 0.5 meter apart (2 feet if the model has been created in US

units). The user can overwrite the number of stations in an object before the

analysis is run using the Assign menu. The user can refine the design along the

length of a member by requesting more stations.

2.4 Demand/Capacity Ratios

Determination of the controlling D/C ratios for each steel frame member indi-

cates the acceptability of the member for the given loading conditions. The

steps for calculating the D/C ratios are as follows:

 The factored forces are calculated for axial, flexural, and shear at each de-

fined station for each design combination. The bending moments are calcu-

Design and Check Stations 2 - 3

Steel Frame Design IS 800:2007

lated about the principal axes. For I-Shape, Box, Channel, T-Shape, Dou-

ble-Angle, Pipe, Circular, and Rectangular sections, the principal axes co-

incide with the geometric axes. For Single-Angle sections, the design con-

siders the principal properties. For General sections, it is assumed that all

section properties are given in terms of the principal directions.

For Single-Angle sections, the shear forces are calculated for directions

along the geometric axes. For all other sections, the program calculates the

shear forces along the geometric and principal axes.

 The design capacities are calculated for compression, tension, bending and

shear based on the equations provided later in this manual. For flexure, the

design capacities are calculated based on the principal axes of bending. For

the I-Shape, Box, Channel, Circular, Pipe, T-Shape, Double-Angle and

Rectangular sections, the principal axes coincide with their geometric axes.

For the Angle sections, the principal axes are determined and all computa-

tions related to flexural stresses are based on that.

The design capacities for shear is calculated along the geometric axes for

all sections. For I-Shape, Box, Channel, T-Shape, Double-Angle, Pipe,

Circular, and Rectangular sections, the principal axes coincide with their

geometric axes. For Single-Angle sections, principal axes do not coincide

with the geometric axes.

 Factored forces are compared to design capacities to determine D/C ratios.

In either case, design codes typically require that the ratios not exceed a

value of one. A D/C ratio greater than one indicates a member that has ex-

ceeded a limit state.

2.5 Design Load Combinations

The design load combinations are the various combinations of the prescribed

load cases for which the structure needs to be checked. The program creates a

number of default design load combinations for steel frame design. Users can

add their own design combinations as well as modify or delete the program de-

fault design load combinations. An unlimited number of design load combina-

tions can be specified.

2 - 4 Design Load Combinations

Chapter 2 Design Algorithms

To define a design load combination, simply specify one or more load cases,

each with its own scale factor. The scale factors are applied to the forces and

moments from the load cases to form the factored design forces and moments

for each design load combination.

For normal loading conditions involving static dead load (DL), live load (LL),

wind load (WL), earthquake load (EL), and dynamic response spectrum load

(EL), the program has built-in default design combinations for the design code.

These are based on the code recommendations.

The default design combinations assume all static load response cases declared

as dead or live to be additive. However, each static load case declared as wind,

earthquake, or response spectrum cases, is assumed to be non-additive with

other loads and produces multiple lateral combinations. Also static wind,

earthquake and notional load responses produce separate design combinations

with the sense (positive or negative) reversed. The notional load cases are add-

ed to load combinations involving gravity loads only.

For other loading conditions involving moving load, time history, pattern live

load, separate consideration of roof live load, snow load, and the like, the user

must define the design load combinations in lieu of or in addition to the default

design load combinations. If notional loads are to be combined with other load

combinations involving wind or earthquake loads, the design load combina-

tions should be defined in lieu of or in addition to the default design load com-

binations.

For multi-valued design combinations, such as those involving response spec-

trum, time history, moving loads and envelopes, where any correspondence

between forces is lost, the program automatically produces sub-combinations

using the maxima/minima values of the interacting forces. Separate combina-

tions with negative factors for response spectrum load cases are not

required because the program automatically takes the minima to be the nega-

tive of the maxima response when preparing the sub-combinations described

previously.

The program allows live load reduction factors to be applied to the member

forces of the reducible live load case on a member-by-member basis to reduce

the contribution of the live load to the factored responses.

Design Load Combinations 2 - 5

Steel Frame Design IS 800:2007

2.6 Second Order P-Delta Effects

Modern design provisions are based on the principle that the member forces are

calculated by a second-order elastic analysis, where the equilibrium is satisfied

on the deformed geometry of the structure. The effects of the loads acting on

the deformed geometry of the structure are known as the second-order or the

P-Delta effects. The P-Delta effects come from two sources: global lateral

translation of the frame and the local deformation of members within the

frame.

Consider the frame object shown in Figure 2-1, which is extracted from a story

level of a larger structure. The overall global translation of this frame object is

indicated by ∆. The local deformation of the member is shown as δ. The total

second order P-Delta effects on this frame object are those caused by both ∆

and δ.

∆

Original position of frame

element shown by vertical

line

Position of frame element

as a result of global lateral

translation,

∆

, shown by

dashed line

Final deflected position of the

frame element that includes the

global lateral translation, ∆, and

the local deformation of the

element,

∆

Original position of frame

element shown by vertical

line

Position of frame element

as a result of global lateral

translation,

∆

, shown by

dashed line

Final deflected position of the

frame element that includes the

global lateral translation, ∆, and

the local deformation of the

element,

Figure 2-1 P-∆ and P-

effects

The program has an option to consider P-Delta effects in the analysis. When

you consider P-Delta effects in the analysis, the program does a good job of

capturing the effect due to the ∆ deformation (P-∆ effect) shown in Figure

2 - 6 Second Order P-Delta Effects

Chapter 2 Design Algorithms

2-1, but it does not typically capture the effect of the δ deformation (P-δ

effect), unless, in the model, the frame object is broken into multiple elements

over its length.

In design codes, required strengths are usually required to be determined using

a second-order analysis that considers both P-∆ and P-δ effects. Approximate

second-order analysis procedures based on amplification of responses from

first-order analysis for calculating the required flexural strengths are common

in current design codes and have the following general form:

( )

δδ

= +

CAP b nt s lt

M MM

where,

CAP

= Required flexural design capacities

= Required flexural capacities from first-order analysis of the

member assuming there is no translation of the frame (i.e., asso-

ciated with the δ deformation in Figure 2-1)

= Required flexural capacities from first-order analysis of the

member as a result of lateral translation of the frame only (i.e.,

associated with the ∆ deformation in Figure 2-1)

= Unitless amplification factor multiplying

( )

nt s lt

A rigorous second order analysis (IS 4.4.2, 4.4.3.1) or the amplification of first

order analysis results to estimate the effect of second order effects (IS 4.1.1,

4.4.3.1, Annex B) is required. The program has the capability of performing

both. In the first case, the required strengths are determined directly from the

analysis results without any amplification factor

s (i.e.,

s is equal to 1). How-

ever, these amplification factors can always be overwritten by the user on a

member-by-member basis, if desired, using the overwrite option.

To properly capture the P-δ effect in a finite element analysis, each element,

especially column elements, must be broken into multiple finite elements,

which is not really desired for other reasons. Although a single element per

member can capture the P-δ effect to some extent, the program considers that

Second Order P-Delta Effects 2 - 7

Steel Frame Design IS 800:2007

inadequate. The program thus uses the

b factor even if the analysis considers

the P-∆ effects. This is a conservative approach.

Thus, in general, the steel frame design feature requires consideration of

P-Delta effects in the analysis before the check/design is performed. Although

one element per line object is generally adequate to capture the P-∆ effect, it is

recommended to use more than one element per line object for the cases where

both P-∆ and P-δ effects are to be considered. However, explicit manual break-

ing of the member into elements has other consequences related to member end

moments and unbraced segment end moment. It is recommended that the

members be broken internally by the program. In this way, the member is

recognized as one unit, end of the members are identified properly, and P-∆

and P-δ effects are captured better.

2.7 Notional Load Cases

Notional loads are lateral loads that are applied at each framing level and are

specified as a percentage of the gravity loads applied at that level (IS 4.3.6).

These are intended to account for the destabilizing effects of out-of-plumbness,

geometric imperfections, inelasticity in structural members, and any other

effects that could induce sway and that are not explicitly considered in the

analysis.

The program allows the user to create a Notional Load case as a percentage of

the previously defined gravity load case to be applied in one of the global lat-

eral directions: X or Y. The user can define more than one notional load case

associated with one gravity load by considering different factors and different

directions.

Currently, the notional loads are automatically included in the default design

load combinations that include lateral loads. Moreover, the user is free to modi-

fy the default design load combinations to include the notional loads with ap-

propriate factors and in appropriate load combinations.

2 - 8 Notional Load Cases

Chapter 2 Design Algorithms

2.8 Member Unsupported Lengths

The column unsupported lengths are required to account for column slender-

ness effects for flexural buckling and for lateral-torsional buckling. The pro-

gram automatically determines the unsupported length ratios, which are speci-

fied as a fraction of the frame object length. Those ratios times the frame object

lengths give the unbraced lengths for the member. Those ratios also can be

overwritten by the user on a member-by-member basis, if desired, using the de-

sign overwrite option.

Two unsupported lengths, L33 and L22, as shown in Figure 2-2 are to be consid-

ered for flexural buckling. These are the lengths between support points of the

member in the corresponding directions. The length L33 corresponds to insta-

bility about the 3-3 axis (major axis), and L22 corresponds to instability about

the 2-2 axis (minor axis). The length LLTB (also termed Lz), not shown in the

figure, is also used for lateral-torsional buckling caused by major direction

bending (i.e., about the 3-3 axis).

Figure 2-2 Unsupported lengths

and

Member Unsupported Lengths 2 - 9

Steel Frame Design IS 800:2007

In determining the values for L22 and L33 of the members, the program recog-

nizes various aspects of the structure that have an effect on these lengths, such

as member connectivity, diaphragm constraints, and support points. The pro-

gram automatically locates the member support points and evaluates the corre-

sponding unsupported length.

It is possible for the unsupported length of a frame object to be evaluated by

the program as greater than the corresponding member length. For example,

assume a column has a beam framing into it in one direction, but not the other,

at a floor level. In that case, the column is assumed to be supported in one di-

rection only at that story level, and its unsupported length in the other direction

will exceed the story height.

By default, the unsupported length for lateral-torsional buckling, LLTB, is taken

to be equal to the L22 factor. Similar to L22 and L33, LLTB can be overwritten.

The unsupported length for minor direction bending for lateral-torsional buck-

ling also can be defined more precisely by using “precise” bracing points in the

Lateral Bracing option, which is accessed using the Design menu > Steel

Frame Design > Lateral Bracing command. This allows the user to define the

lateral bracing of the top, bottom, or both flanges. The bracing can be a point

brace or continuous bracing.

The program calculates the unbraced length to determine axial capacity based

on the limit state of flexural buckling from this definition. Any bracing at the

top or bottom, or both, is considered enough for flexural buckling in the minor

direction. While checking moment capacity for the limit state of lateral-

torsional buckling (LTB) at a station the program dynamically calculates the

bracing points on the compression flange at the left and at the right of the

check station considering the sign of the moment diagram. This definition af-

fects only the unbraced lengths for minor direction bending (L22) and lateral-

torsional buckling (LLTB). This “exact” method of bracing definition does not

allow the user to define unbraced lengths for major direction bending (L33).

There are three sources of unbraced length ratio: (1) “automatic” calculation,

(2) “precise” bracing definition, (3) overwrites, with increasing priority in con-

siderations. “Automatic” calculation of the unbraced length is based on mem-

ber connectivity considering only the members that have been entered into the

model. This misses the tiny bracing members. However, such automatically

calculated bracing lengths are load combo (moment diagram) independent.

2 - 10 Member Unsupported Lengths

Chapter 2 Design Algorithms

This can be reported easily. Similarly, the overwritten values are load combo

independent. This allows the program to report the overwritten unbraced length

easily. However, if the member has a “precise” bracing definition, the unbraced

length can be different at different stations of the member along the length. Al-

so it can be load combo dependent. Thus, when the unbraced length is reported

in the detailed design info, it is reported perfectly considering all three sources

as needed. However, when reporting unbraced length on the model shown in

the active window, the program-reported value comes from “automatic” calcu-

lation or from the overwrites if the user has overwritten it.

2.9 Effective Length Factor (K)

The effective length method for calculating member axial compressive strength

has been used in various forms in several stability based design codes. The

method originates from calculating effective buckling lengths, KL, and is based

on elastic/inelastic stability theory. The effective buckling length is used to

calculate an axial compressive strength, Nb,Rd, through an empirical column

curve that accounts for geometric imperfections, distributed yielding, and

residual stresses present in the cross-section.

There are two types of K-factors in the “Indian IS 800:2007” code. The first

type of K-factor is used for calculating the Euler axial capacity assuming that

all of the member joints are held in place, i.e., no lateral translation is allowed.

The resulting axial capacity is used in calculation of the k factor. This K-factor

is named as K1 in this document. This K1 factor is always less than 1 and is not

calculated. By default the program uses the value of 1 for K1. The program al-

lows the user to overwrite K1 on a member-by-member basis.

The other K-factor is used for calculating the Euler axial capacity assuming

that all the member joints are free to sway, i.e., lateral translation is allowed.

The resulting axial capacity is used in calculating Pd. This K-factor is named K2

in this document. This K2 is always greater than 1 if the frame is a sway frame.

The program calculates the K2 factor automatically based on sway condition.

The program also allows the user to overwrite K2 factors on a member-by-

member basis. If the frame is not really a sway frame, the user should over-

write the K2 factors.

Effective Length Factor (K) 2 - 11

Steel Frame Design IS 800:2007

Both K1 and K2 have two values: one for major direction and the other for mi-

nor direction, K1minor, K1major, K2minor, K2major.

There is another K-factor, Kltb, for lateral-torsional buckling. By default, Kltb is

taken as equal to K2minor. However, the user can overwrite this on a member-by-

member basis.

The rest of this section is dedicated to the determination of K2 factors.

The K-factor algorithm has been developed for building-type structures, where

the columns are vertical and the beams are horizontal, and the behavior is basi-

cally that of a moment-resisting frame for which the K-factor calculation is rel-

atively complex. For the purpose of calculating K-factors, the objects are iden-

tified as columns, beams, and braces. All frame objects parallel to the Z-axis

are classified as columns. All objects parallel to the X-Y plane are classified as

beams. The remainders are considered to be braces.

The beams and braces are assigned K-factors of unity. In the calculation of the

K-factors for a column object, the program first makes the following four stiff-

ness summations for each joint in the structural model:

cx cx

cE I



=



∑

bx bx

cE I



=



∑

cy cy

cE I



=



∑

by by

cE I



=



∑

where the x and y subscripts correspond to the global X and Y directions and

the c and b subscripts refer to column and beam. The local 2-2 and 3-3 terms

22 22

EI L

and

33 33

EI L

are rotated to give components along the global X and

Y directions to form the

( )

EI L

and

( )

EI L

values. The correlation factor

for effective flexural stiffness, c, is taken as 1, disregarding the code recom-

mendation (IS Table 35). Then for each column, the joint summations at END-

I and the END-J of the member are transformed back to the column local 1-2-3

coordinate system, and the β-values for END-I and the END-J of the member

are calculated about the 2-2 and 3-3 directions as follows:

2 - 12 Effective Length Factor (K)

Chapter 2 Design Algorithms

22 22

β= +

22 22

β= +

33 33

β= +

33 33

β= +

Finally, if

and

βJ

are known for a particular direction, the column K-

factors for the corresponding direction is calculated from the following rela-

tionship for α:

( )

0.5

1 2 12

1 0.2 0.12

1 0.8 0.6



− β +β − ββ

=

− β +β + ββ



This relationship is the mathematical formulation for the evaluation of K-

factors for moment-resisting frames assuming sidesway to be uninhibited. For

other structures, such as braced frame structures, the K-factors for all members

are usually unity and should be set so by the user. The following are some im-

portant aspects associated with the column K-factor algorithm:

 An object that has a pin at the joint under consideration will not enter the

stiffness summations calculated previously. An object that has a pin at the

far end from the joint under consideration will contribute only 50% of the

calculated EI value. Also, beam members that have no column member at

the far end from the joint under consideration, such as cantilevers, will not

enter the stiffness summation.

 If rotational releases exist at both ends of an object for a particular direc-

tion, the corresponding K-factor is set to unity.

 The automated K-factor calculation procedure can occasionally generate

artificially high K-factors, specifically under circumstances involving

skewed beams, fixed support conditions, and under other conditions where

the program may have difficulty recognizing that the members are laterally

supported and K-factors of unity are to be used.

 All K-factors produced by the program can be overwritten by the user.

These values should be reviewed and any unacceptable values should be

replaced.

 The beams and braces are assigned K-factors of unity.

Effective Length Factor (K) 2 - 13

Steel Frame Design IS 800:2007

The effective length factor K1 of column in non-sway frames is given by

()

1 2 12

1 0.145 0.265

2 0.364 0.247



+ β +β − ββ



=

− β +β − ββ



If the member is assigned with a framing type of sway frame, K1 is used for Kz

and Ky calculation, and K2 is used for Pd calculation. If the member is assigned

with a framing type of Braced frame, K1 is used for both Kz and Ky calculation

and also for Pd calculation.

2.10 Effect of Breaking a Member into Multiple Elements

The preferred method is to model a beam, column or brace member as one sin-

gle element. However, the user can request that the program break a member

internally at framing intersections and at specified intervals. In this way, accu-

racy in modeling can be maintained at the same time that design/check specifi-

cations can be applied accurately. There is special emphasis on the end forces

(moments in particular) for many different aspects of beam, column, and brace

design. If the member is manually meshed (broken) into segments, maintaining

the integrity of the design algorithm becomes difficult.

Manually breaking a column member into several elements can affect many

things during design in the program.

1. The unbraced length: The unbraced length is really the unsupported length

between braces. If no intermediate brace is present in the member, the un-

braced length is typically calculated automatically by the program from the

top of the flange of the beam framing the column at the bottom to the bot-

tom of the flange of the beam framing the column at the top. The automati-

cally calculated length factor typically becomes less than 1. If there are in-

termediate bracing points, the user should overwrite the unbraced length

factor in the program. The user should choose the critical (larger) one.

Even if the user breaks the element, the program typically picks up the un-

braced length correctly, provided that there is no intermediate bracing

point.

2. K-factor: Even if the user breaks the member into pieces, the program typi-

cally can pick up the K-factors correctly. However, sometimes it can not.

2 - 14 Effect of Breaking a Member into Multiple Elements

Chapter 2 Design Algorithms

The user should note the K-factors. All segments of the member should

have the same K-factor and that factor should be calculated based on the

entire member. If the calculated K-factor is not reasonable, the user can

overwrite the K-factors for all the segments.

3. Cm factor: The Cm factor should be based on the end moments of unbraced

lengths of each member and should not be based on the end moments of

the member. The program already calculates the Cm factors based on the

end moments of unbraced lengths of each segment. If the break-up points

are the brace points, no action is required by the user. If the broken seg-

ments do not represent the brace-to-brace unsupported length, the program

calculated Cm factor is conservative. If this conservative value is accepta-

ble, no action is required by the user. If it is not acceptable, the user can

calculate the Cm factor manually for the critical combination and overwrite

its value for that segment.

4. C1 factor: The logic is similar to that for the Cm factor.

5. Kz, Ky, and KLT factors: This factor amplifies the factored moments for the

P-

effect. In its expression, there are the Cm factor and the Euler Buckling

capacity Pe. If the user keeps the unbraced length ratios (L33 and L22) and

the K-factors (K33 and K,22) correct, the Kz, Ky, and KLT factors would be

correct.

If the user models a column with a single element and makes sure that the

L-factors and K-factors are correct, the effect of Kz, Ky, and KLT factors will be

picked up correctly. The factors Cm and C1 will be picked up correctly if there

is no intermediate bracing point. The calculated Cm and C1 factors will be

slightly conservative if there are intermediate bracing points.

If the user models a column with multiple elements and makes sure that

l-factors and ke-factor are correct, the effect of Kz, Ky, and KLT factors will be

picked up correctly. The factors Cm and C1 will be picked up correctly if the

member is broken at the bracing points. The calculated Cm and C1 factors will

be conservative if the member is not broken at the bracing points.

Effect of Breaking a Member into Multiple Elements 2 - 15

Steel Frame Design IS 800:2007

2.11 Supported Framing Types

The code (IS 800:2007) recognizes the following types of framing

systems.

Framing Type

References

SMF (Special Moment Frame)

IS 12.11

OMF (Ordinary Moment Frame)

IS 12.10

SCBF (Special Concentrically Braced Frame)

IS 12.7

OCBF (Ordinary Concentrically Braced Frame)

IS 12.8

EBF ( Eccentrically Braced Frame)*

IS 12.9

Secondary or Gravity only

IS 12.1

*No special provision for EBF is programmed.

2.12 Continuity Plates

In a plan view of a beam/column connection, a steel beam can frame into a

column in the following ways:



The steel beam frames in a direction parallel to the column major direction,

i.e., the beam frames into the column flange.



The steel beam frames in a direction parallel to the column minor direction,

i.e., the beam frames into the column web.



The steel beam frames in a direction that is at an angle to both of the princi-

pal axes.

To achieve a beam/column moment connection, continuity plates, such as

shown in Figure 2-3, are usually placed on the column, in line with the top and

bottom flanges of the beam, to transfer the compression and tension flange

forces of the beam into the column.

For connection conditions described in the last two bullet items, the thickness

of such plates is usually set equal to the flange thickness of the corresponding

beam.

2 - 16 Supported Framing Types

Chapter 2 Design Algorithms

Figure 2-3 Doubler Plates and Continuity Plates

Continuity Plates 2 - 17

Steel Frame Design IS 800:2007

However, for the connection condition described by the first bullet item, where

the beam frames into the flange of the column, such continuity plates are not

always needed. The requirement depends on the magnitude of the beam flange

force and the properties of the column.

The program investigates whether the continuity plates are needed based on the

requirements of the selected code. Columns of I-sections supporting beams of

I-sections only are investigated. The program evaluates the continuity plate re-

quirements for each of the beams that frame into the column flange and reports

the maximum continuity plate area that is needed for each beam flange. The

continuity plate requirements are evaluated for moment frames only.

2.13 Doubler Plates

One aspect of the design of a steel framing system is an evaluation of the shear

forces that exist in the region of the beam-column intersection known as the

panel zone. Shear stresses seldom control the design of a beam or column

member. However, in a moment resisting frame, the shear stress in the beam-

column joint can be critical, especially in framing systems when the column is

subjected to major direction bending and the web of the column resists the joint

shear forces. In minor direction bending, the joint shear is carried by the col-

umn flanges, in which case the shear stresses are seldom critical, and the pro-

gram does therefore not investigate this condition.

Shear stresses in the panel zone due to major direction bending in the column

may require additional plates to be welded onto the column web, depending on

the loading and the geometry of the steel beams that frame into the column, ei-

ther along the column major direction, or at an angle so that the beams have

components along the column major direction. See Figure 2-3. When code ap-

propriate, the program investigates such situations and reports the thickness of

any required doubler plates. Only columns with I-shapes and only supporting

beams with I-shapes are investigated for doubler plate requirements. Also,

doubler plate requirements are evaluated for moment frames only.

2 - 18 Doubler Plates

Chapter 2 Design Algorithms

2.14 Frame Design Procedure Overwrites

The structural model may contain frame elements made of several structural

materials: steel, concrete, aluminum, cold-formed steel and other materials.

The program supports separate design procedures for each material type. By

default the program determines the design procedure from the material of the

frame member.

The program allows the user to turn the design of specific members off and on

by selecting No Design or Default from material. Overwriting the design pro-

cedure can be accessed from the Design menu > Overwrite Frame Design

Procedure command.

ETABS supports both regular steel frame design and composite beam design.

The determination of design procedure is different. If the material is concrete,

the design procedure is concrete. If the material is steel, the default design pro-

cedure can be steel frame design or composite beam design. If the section is of

steel material, and the member satisfies a host of other criteria, such as the

member is horizontal (beam), it supports a filled deck or slab, it is an I-shaped

member, it is hinged at both ends and so on, then the default design procedure

is taken as composite beam design; otherwise, the default design procedure is

taken as steel frame design. ETABS allows the user to overwrite a steel mem-

ber frame design procedure to steel frame design, composite beam design, de-

fault, or no design. Change the design procedure by selecting the member(s)

and clicking the Design menu > Overwrite Frame Design Procedure com-

mand. A change in design will be successful only if the design procedure is

valid for that member, i.e., the program will not allow the user to change the

design procedure for a steel frame object to concrete frame design.

2.15 Interactive Design

Interactive Design is a powerful mode that allows the user to review the design

results for any steel frame design and interactively revise the design assump-

tions and immediately review the revised results. Note that a design must have

been run for the interactive design mode to be available. Refer to the program

Help for more information about interactive design.

Frame Design Procedure Overwrites 2 - 19

Steel Frame Design IS 800:2007

2.16 Automated Iterative Design

If Auto Select sections have been assigned to frame objects, ETABS can auto-

matically perform the iterative steel frame design process. To initiate the pro-

cess, first use the Design menu > Steel Frame Design > View/Revise Prefer-

ence command and set the maximum number of auto iterations to the maxi-

mum number of design iterations the program is to run automatically. Next, run

the analysis. Then, begin design of the structure, making sure that no objects

are selected.

The program will then start the cycle of (1) performing the design, (2) compar-

ing the last-used Analysis Sections with the Design Sections, (3) setting the

Analysis Sections equal to the Design Sections, and (4) rerunning the analysis.

This cycle will continue until one of the following conditions has been met:

 The Design Sections and the last-used Analysis Sections are the same.

 The number of iterations performed is equal to the number of iterations

specified for the maximum number on the Preferences form.

Currently, this feature is absent in SAP2000.

2.17 Choice of Units

English as well as SI and MKS metric units can be used for input. The codes

are based on a specific system of units. All equations and descriptions present-

ed in the subsequent chapters correspond to that specific system of units unless

otherwise noted. For example, the IS 800:2007 code is published in millimeter-

Newton-second units. By default, all equations and descriptions presented in

this manual correspond to millimeter-Newton-second units. However, any sys-

tem of units can be used to define and design a structure in the program.

2 - 20 Automated Iterative Design

Steel Frame Design IS 800:2007

Chapter 3

Design using IS 800:2007

This chapter provides a detailed description of the algorithms used by the

programs in the design/check of structures in accordance with “IS 800:2007 –

Indian Standard: General Construction in Steel – Code of Practice” (IS 2007).

The implementation covers load combinations from “IS 800:2007,” which is

described in Section 3.4 Design Loading Combinations in this chapter. The

loading based on "IS 1893:2002" and “IS 875:1987” has been described in a

separate document entitled “Automated Lateral Loads Manual” (IS 2007; CSI

2007).

For referring to pertinent sections of the corresponding code, a unique prefix is

assigned for each code.

• Reference to the IS 800:2007 code is identified with the prefix “IS.”

• Reference to the IS 1893 (Part 1):2002 code is identified with the prefix

“IS 1893.”

• Reference to the IS 875 (Part 3):1997 code is identified with the prefix "IS

875."

• Reference to the ANSI/AISC 360-05 code (specialist literature) is identi-

fied with the prefix “AISC.”

3 - 1 Notations

3.1 Notations

The following table provides a list of the symbols used in this manual, along

with a short description. Where possible, the symbol from the design code is

used in this manual.

Cross-sectional area, mm2

Effective section area, mm2

Gross cross-sectional area, mm2

Net effective area of cross-section, mm2

Shear area, mm2

, A

Major and minor shear areas, mm2

Web area, mm2

Nominal dimension of plate in a section, mm

Flange width, mm

Modification factor for elastic critical moment

mLT

Equivalent uniform moment factor for lateral-torsional buck-

ling

Equivalent uniform moment factor for minor bending

Equivalent uniform moment factor for major bending

Outside diameter of pipes, mm

Overall depth or clear depth of member depending on section

type, mm

Modulus of elasticity, N/mm2

fcc Euler buckling stress =

()

KLr

Design compressive stress, N/mm2

Steel ultimate strength, N/mm2

Steel yield strength, N/mm2

Steel yield strength of the web, N/mm2

Shear modulus, N/mm

Overall depth of the section, mm

Web height, mm

Moment of inertia, mm

, I

Minor moment of inertia, mm

Major moment of inertia, mm4

St. Venant torsional constant for the section, mm

Effective length factor

, K

Effective length K-factors in the major and minor directions

Moment magnification factor for lateral-torsional buckling

LTB

Effective length K-factor for lateral-torsional buckling

Moment magnification factor for minor axis bending moment

Moment magnification factor for major axis bending moment

Laterally unbraced length of member, mm

, L

Laterally unbraced length of member for major and minor ax-

es bending, mm

Effective buckling length, mm

LTB

Unbraced length for lateral-torsional buckling, mm

Design factored bending moment, N-mm

Design bending resistance, N-mm

Reduced design bending resistance accounting for shear,

N-mm

, M

Design bending moment about minor axis bending, N-mm

, M

Design bending moment about major axis bending, N-mm

Factored applied axial force (tension, T, or compression, P)

Elastic critical force, N

Design strength in tension, T

, or compression strength due to

yielding given by

0d gy m

N Af= γ

Design axial compression force, N

Design compressive strength, N

Radius of gyration, mm

, r

Radii of gyration in the major and minor directions, mm

Least radius of gyration for analysis sections, mm

Plate thickness, mm

Design tension resistance, N

Design tensile strength due to yielding of cross-section, N

Design ultimate tensil strength due to rupture, N

Flange thickness, mm

Web thickness, mm

Design factored shear force, N

Design shear buckling resistance, N

Design shear strength, N

Elastic section modulus, mm

e33

e22

Major and minor elastic section moduli, mm3

Plastic modulus, mm3

p33

p22

Major and minor plastic section moduli, mm

Value for calculating the reduction factor

Value for calculating the reduction factor χ

Imperfection factor for axial compression

Imperfection factor for lateral-torsional buckling

, α

Coefficients used in an interaction equation (IS 9.3.1.1)

Reduction factor of moment capacity to account for shear

forces

Moment capacity adjustment factor for appropriate class of

section

Stress reduction factor for buckling

Stress reduction factor for lateral-torsional buckling

Coefficient dependent on fy,

250

Partial factor for the resistance of cross-sections and buckling

Partial factor for the resistance governed by ultimate stress

λ Non-dimensional slenderness,

rEπ

for flexural buckling

,λ

Slenderness parameters for classification

Non-dimensional slenderness for lateral-torsional buckling

Non-dimensional web slenderness ratio

Ratio of moments in a segment

3.2 Design Preferences

The steel frame design preferences are basic assignments that apply to all steel

frame members. Table 3-1 lists steel frame design preferences for "Indian IS

800:2007." Default values are provided for all preference items. Thus, it is not

necessary to specify or change any of the preferences. However, at least review

the default values to ensure they are acceptable. Some of the preference items

also are available as member-specific Overwrite items. The overwrites are

described in the next section. Overwritten values take precedence over the

preferences. Refer to the program Help for information about changing Preferences.

Table 3-1: Steel Frame Design Preferences

Item Possible Values Default Value Description

Design Code Design codes

available in the

current version

AISC360-05/

IBC 2006 The selected design code. Subsequent design is based

on this selected code.

Table 3-1: Steel Frame Design Preferences

Item Possible Values Default Value Description

Multi-Response Case

Design Envelopes,

Step-by-Step, Last

Step, Envelopes,

All, Step-by-Step -

All

Envelopes Select to indicate how results for multivalued cases

(Time history, Nonlinear static or Multi-step static)

are considered in the design. Envelope considers

enveloping values for Time History and Multi-step

static and last step values for Nonlinear static. Step-

by-Step considers step-by-step values for Time His-

tory and Multi-step static and last step values for

Nonlinear static. Last Step considers last values for

Time History, Multi-step static and Nonlinear static.

Envelope - All considers enveloping values for Time

History, Multi-step static and Nonlinear static. Step-

by-Step - All considers step-by-step values for Time

History, Multi-step static and Nonlinear static. Step-

by-Step and Step-by-Step - All default to the corre-

sponding Envelope if more then one multivalued

case is present in the combo.

Framing Type SMF, OMF, SCBF,

OCBF, EBF,

Secondary

SMF This item is used for ductility considerations in the

design.

Importance Factor > 0 1.0

This is related to seismic design. This depends on the

functional use of the structure, hazardous conse-

quences of its failure, post-earthquake functional

needs, and so on (IS 1893 6.4.2).

Seismic Zone Zone I, II, III, IV, V Zone V This affects seismic intensity. It depends on physical

location of the structure (IS 1893 6.4.2, Table 2,

Annex E).

Consider P-Delta

Done? Yes/No It affects K-factor calculation. If P-∆ analysis is

completed, K is taken as if the structure is braced.

GammaM0 > 0 1.1 Partial factor for the resistance of cross-sections and

buckling.

GammaM1 > 0 1.25 Partial factor for the resistance of members to

ultimate stress.

Ignore Seismic Code? Yes, No No Toggle to consider (No) or not consider (Yes) the

seismic part of the code in design.

Ignore Special

Seismic Load? Yes, No No Toggle to consider (No) or not consider (Yes) special

seismic load combinations in design.

Is Doubler Plate Plug

Welded? Yes, No Yes Toggle to indicate if the doubler-

plate is plug welded

(Yes), or it is not plug welded (No).

Consider

Deflection? Yes, No Yes Toggle to consider the deflection limit (Yes) or to not

consider the deflection limit (No).

Table 3-1: Steel Frame Design Preferences

Item Possible Values Default Value Description

DL Limit, L/ ≥ 0 120 Deflection limit for dead load. Inputting 120 means

that the limit is L/120. Inputting zero means no check

will be made of this item.

Super DL+LL Limit, L/

≥ 0 120 Deflection limit for superimposed dead plus live

load. Inputting 120 means that the limit is L/120.

Inputting zero means no check will be made of this

item.

Live Load Limit, L/ ≥ 0 360

Deflection limit for superimposed live load. Inputting

360 means that the limit is L/360. Inputting zero

means no check will be made of this item.

Total Limit, L/ ≥ 0 240 Deflection limit for total load. Inputting 240 means

that the limit i

s L/240. Inputting zero means no check

will be made of this item.

Total-Camber Limit, L/ ≥ 0 240 Limit for net deflection. Camber is subtracted from

the total load deflection to get net deflection. Input-

ting 240 means that the limit is L/240. Inputting zero

means no check will be made of this item.

Pattern Live Load

Factor ≤1.0 0.75 The live load factor for automatic generation of load

combinations involving pattern live loads and dead

loads.

Demand/Capacity

Ratio Limit ≤1.0 0.95 The demand/capacity ratio limit to be used for ac-

ceptability. D/C ratios that are less than or equal to

this value are considered acceptable.

3.3 Overwrites

The steel frame design Overwrites are basic assignments that apply only to

those elements to which they are assigned. Table 3-2 lists steel frame design

overwrites for "Indian IS 800:2007." Default values are provided for all Over-

write items. Thus, it is not necessary to specify or change any of the Over-

writes. However, at least review the default values to ensure they are accepta-

ble. When changes are made to Overwrite items, the program applies the

changes only to the elements to which they are specifically assigned. Overwrit-

ten values take precedence over the Preferences. Refer to the program Help for

information about changing Overwrites.

Many of the items on the Overwrites form are similar to those found on the

Preferences form.

Table 3-2 Steel Frame Design Overwrites for "Indian IS 800:2007"

Item Possible Values Default Value Description

Current Design

Section Any defined steel

section Analysis

section The design section for the selected frame object.

When this Overwrite is applied, any previous auto

select section assigned to the frame object is

removed.

Fame Type SMF, OMF, SCBF,

OCBF, EBF, Secondary

From

Preferences This item is used for ductility considerations in the

design.

Section Class Plastic,

Compact,

Semicompact,

Slender

Program

determined Section class to be used. This can be “Class 1,”

“Class 2,” “Class 3,” or “Class 4.” It determines the

capacity of the sections and the interaction equations

to be used. If not overwritten, it is calculated based

on Table 2 of the code.

Column Buckling

Curve (z-z) a, b, c, or d Program

determined Column buckling curve to be used for flexural buck-

ling about the major axis. This determines the axial

compression capacity for buckling about the major

axis. It determines the imperfection factors for buck-

ling curve. If not overwritten, it is taken from Table

10 of the code.

Column Buckling

Curve (y-y) a, b, c, or d Program

determined Column buckling curve to be used for flexural buck-

ling about the minor axis. This determines the axial

compression capacity for buckling about the minor

axis. It determines the imperfection factors for buck-

ling curve. If not overwritten, it is taken from Table

10 of the code.

Is Rolled Section? Yes./No Program

determined It might affect the column buckling curve determina-

tion.

Consider Deflection?

Yes/No No Toggle to consider (Yes) or not consider (No) deflec-

tion.

Deflection Check

Type Ratio,

Absolute,

Both

Program

Determined Choose to consider deflection limitations as absolute,

as a divisor of the beam length (relative), or both.

DL Limit, L/ ≥ 0 Program

Determined Deflection limit for dead load. Inputting 120 means

that the limit is L/120. Inputting zero means no check

will be made of this item.

Super DL+LL

Limit, L/ ≥ 0 Program

Determined Deflection limit for superimposed dead plus live

load. Inputting 120 means that the limit is L/120.

Inputting zero means no check will be made of this

item.

Live Load Limit, L/ ≥ 0 Program

Determined

Deflection limit for superimposed live load. Inputting

360 means that the limit is L/360. Inputting zero

means no check will be made of this item.

Total Limit, L/ ≥ 0 Program

Determined Deflection limit for total load. Inputting 240 means

that the limit is L/240. Inputting zero means no check

will be made of this item.

Table 3-2 Steel Frame Design Overwrites for "Indian IS 800:2007"

Item Possible Values Default Value Description

Total-

Camber Limit,

L/ ≥ 0 Program

Determined Limit for net deflection. Camber is subtracted from

the total load deflection to get net deflection. Input-

ting 240 means that the limit is L/240. Inputting zero

means no check will be made of this item.

DL Limit, abs ≥ 0 Program

Determined Deflection limit for dead load. Inputting zero means

no check will be made of this item.

Super DL+LL Limit,

abs ≥ 0 Program

Determined Deflection limit for superimposed dead plus live

load. Inputting zero means no check will be made of

this item.

Live Load Limit, abs

≥ 0 Program

Determined

Deflection limit for superimposed live load. Inputting

zero means no check will be made of this item.

Total Limit, abs ≥ 0 Program

Determined Deflection limit for total load. Inputting zero means

no check will be made of this item.

Total–

Camber Limit,

abs ≥ 0 Program

Determined Deflection limit for net deflection. Camber is sub-

tracted from the total load deflection to get net

deflection. Inputting a value of 240 means that the

limit is L/240. Inputting zero mea

ns no check will be

made of this item.

Specified Camber ≥ 0 Program

Determined

The specified amount of camber to be reported in the

design output and to be used in the net deflection

check.

Net Area to Total

Area Ratio ≥ 0 Program

Determined The ratio of the net area at the design section to gross

cross-sectional area of the section. This ratio affects

the design of axial tension members. Specifying 0

means the value is program default which is 1.

Live Load Reduction

Factor ≥ 0 Program

Determined The

reducible live load is multiplied by this factor to

obtain the reduced live load for the frame object.

Specifying zero means the value is program deter-

mined.

Unbraced Length

Ratio (Major) ≥ 0 Program

Determined Unbraced length factor for buckling about the frame

object major axis; specified as a fraction of the frame

object length. This factor times the frame object

length gives the unbraced length for the object. Spec-

ifying zero means the value is program determined.

Unbraced Length

Ratio (Minor) ≥ 0 Program

Determined

Unbraced length factor for buckling about the frame

object minor axis; specified as a fraction of the frame

object length. This factor times the frame object

length gives the unbraced length for the object. Spec-

ifying zero means the value is program determined.

Unbraced Length

Ratio (LTB) ≥ 0 Program

Determined Unbraced length factor for lateral-torsional buckling

for the frame object; specified as a fraction of the

frame object length. This factor times the frame

object length gives the unbraced length for the ob-

ject. Specifying zero means the value is program

determined.

Table 3-2 Steel Frame Design Overwrites for "Indian IS 800:2007"

Item Possible Values Default Value Description

Effective Length

Factor Braced (K1

Major)

≥ 0 1.0 Effective length factor for buckling about the frame

object major axis; specified as a frac

tion of the frame

object length. This factor times the frame object

length gives the effective length for the object. Spec-

ifying zero means the value is program determined.

For beam design, this factor is always taken as 1,

regardless of any other value specified in the Over-

writes. This factor is used calculating Ky, Kz and KLT

factors.

Effective Length

Factor Braced

(K1 Minor)

≥ 0 Program

Determined Effective length factor for buckling about the frame

object minor axis; specified as a frac

tion of the frame

object length. This factor times the frame object

length gives the effective length for the object. Spec-

ifying zero means the value is program determined.

For beam design, this factor is always taken as 1,

regardless of any other value specified in the Over-

writes. This factor is used calculating Ky, Kz and KLT

factors.

Effective Length

Factor Sway (K2

Major)

≥ 0 Calculated Effective length factor for buckling about the frame

object major axis assuming that the frame is not

braced at the joints against sidewsway; specified as a

fraction of the frame object length. This factor times

the frame object length gives the effective length for

the object. Specifying zero means the value is pro-

gram determined. For beam design, this factor is

always 1, regardless of any other values specified in

the Overwrites. The factor is used for axial compres-

sion capacity.

Effective Length

Factor Sway (K2

Minor)

≥ 0 Calculated Effective length factor for buckling about the frame

object minor axis assuming that the frame is not

braced at the joints

against sidewsway; specified as a

fraction of the frame object length. This factor times

the frame object length gives the effective length for

the object. Specifying zero means the value is pro-

gram determined. For beam design, this factor is

always 1, regardless of any other values specified in

the Overwrites. The factor is used for axial compres-

sion capacity.

Effective Length

Factor (K LTB) ≥ 0 Program

Determined Effective length factor for lateral-torsional buckling;

specified as a fraction of the frame object length.

This factor times the frame object length gives the

effective length for the object. Specifying zero means

the value is program determined. For beam design,

this factor is taken as 1 by default. The values should

be set by the user.

Bending Coefficient

(C1) ≥ 0

Program

Determined Unitless factor; C1 is used in determining the critical

buckling moment, Mcr, for arbitrary moment dia-

gram. Inputting zero means the value is program

determined.

Table 3-2 Steel Frame Design Overwrites for "Indian IS 800:2007"

Item Possible Values Default Value Description

Uniform Moment

Factor (Cmz) ≥ 0

Calculated Unitless factor; Cm for major axis bending is used in

determining the interaction ratio. Inputting zero

means the value is program determined.

Uniform Moment

Factor (Cmy) ≥ 0

Calculated Unitless factor; Cm for minor

axis bending is used in

determining the interaction ratio. Inputting zero

means the value is program determined.

Uniform Moment

Factor (CmLT) ≥ 0

Program

Determined Unitless factor; CmLT for lateral torsional buckling

is used in de

termining the interaction ratio. Inputting

zero means the value is program determined.

Moment Coefficient

(Kz) ≥ 0

Program

Determined Unitless moment magnification factor for major axis

bending moment. Specifying zero means the value is

program determined.

Moment Coefficient

(Ky) ≥ 0

Program

Determined Unitless moment magnification factor for minor axis

bending moment. Specifying zero means the value is

program determined.

Moment Coefficient

(K_LT) ≥ 0

Program

Determined Unitless moment magnification factor for lateral-

torsional buckling. Specifying zero means the value

is program determined.

Yield Stress, Fy ≥ 0

From

Material Material yield strength used in the design/check.

Specifying zero means the value is program deter-

mined. The program determined value is taken from

the material property assigned to the frame object.

Compressive

Capacity, Pd ≥ 0

Calculated Design axial compressive capacity. Specifying zero

means the value is program determined.

Tensile Capacity, Td ≥ 0

Calculated Design axial tensile capacity. Specifying zero means

the value is program determined.

Major Bending

Capacity, Mdz ≥ 0

Calculated Design bending moment capacity in major axis bend-

ing. Specifying zero means the value is program

determined.

Minor Bending

Capacity, Mdy ≥ 0

Calculated Design bending moment capacity in minor axis bend-

ing. Specifying zero means the value is program

determined.

Critical Buckling

Moment, Mcr

Elastic critical moment calculated in accordance with

Annex E.

Major Shear

Capacity, Vdy ≥ 0

Calculated Design shear capacity force for major direction

shear. Specifying zero means the value is program

determined.

Minor Shear

Capacity, Vdz ≥ 0

Calculated Design shear capacity force for minor direction

shear. Specifying zero means the value is program

determined.

Table 3-2 Steel Frame Design Overwrites for "Indian IS 800:2007"

Item Possible Values Default Value Description

Demand/Capacity

Ratio Limit ≥ 0 Calculated The demand/capacity ratio limit to be used for

acceptability. Demand/capacity ratios that are less

than or equal to this value are considered acceptable.

Specifying 0 means the value is program determined.

3.4 Design Loading Combinations

The structure is to be designed so that its design strength equals or exceeds the

effects of factored loads stipulated by the applicable design code. The default

design combinations are the various combinations of the already defined analy-

sis cases, such as dead load (DL), live load (LL), wind load (WL), and horizon-

tal earthquake load (EL).

For the IS 800:2007 code, the following default design combinations are gen-

erated by the program (IS 3.5.1, 5.3.3, Table 4):

1.5DL (IS 3.5.1, 5.3.3, Table 4, Line 1)

1.5DL + 1.5L (IS 3.5.1, 5.3.3, Table 4, Line 2)

1.5DL ± 1.5WL (IS 3.5.1, 5.3.3, Table 4, Line 4)

0.9DL ± 1.5WL (IS 3.5.1, 5.3.3, Table 4, Line 4)

1.2D + 1.2WL + 1.2W (IS 3.5.1, 5.3.3, Table 4, Line 3)

1.2D + 1.2L ± 0.6W (IS 3.5.1, 5.3.3, Table 4, Line 2)

1.5D ± 1.5E (IS 3.5.1, 5.3.3, Table 4, Line 4)

0.9D ± 1.5E (IS 3.5.1, 5.3.3, Table 4, Line 4)

1.2D + 1.2L ± 1.2E (IS 3.5.1, 5.3.3, Table 4, Line 3)

The code is required to consider Notional Load in the design loading combina-

tions for steel frame design. The program allows the user to define and create

notional loads as individual load cases from a specified percentage of a given

gravity load acting in a particular lateral direction. These notional load cases

should be considered in the combinations with appropriate factors, appropriate

directions, and appropriate senses. Notional loads are automatically included in

the default design load combinations that do not include lateral loads. Notional

load patterns are only added to a load combination when their corresponding

gravity load patterns are included in that combination, using the corresponding

scale factor. For further information, refer to the "Notional Load Cases" section

in Chapter 2.

The combinations described herein are the default loading combinations only.

They can be deleted or edited as required by the design code or engineer-of-

record. The program allows live load reduction factors to be applied to the

member forces of the reducible live load case on a member-by-member basis

to reduce the contribution of the live load to the factored responses.

Live load reduction factors can be applied to the member forces of the live load

case on a member-by-member basis to reduce the contribution of the live load

to the factored loading. However, such a live load case must be specified as

type Reducible Live Load.

3.5 Design Strength

The design strength for steel shapes is obtained by dividing the ultimate

strength of the shape by a partial factor of safety, γm. The values of γm used in

the program are as follows:

Partial safety factor for buckling and yielding, γm0 = 1.10 (IS 5.4.1, Table 5)

Partial safety factor for ultimate stress γm1 = 1.25. (IS 5.4.1, Table 5)

Although not recommended, the program allows them to be overwritten in the

preferences. If they are overwritten, the program uses them consistently.

3.6 Classification of Sections for Local Buckling

For the determination of the design strengths for axial compression and flex-

ure, the sections are classified as Plastic (Class 1), Compact (Class 2), Semi-

Compact (Class 3), or Slender (Class 4). The program classifies the individual

sections in accordance with Table 3-3 (IS 3.7.2, Table 2). As specified in that

table, a section is classified as Class 1, Class 2, Class 3 or Class 4 as applica-

ble.

For a section to qualify as Plastic (Class 1), its flanges must be continuously

connected to the web or webs and the width-thickness ratios of its compression

elements must not exceed the limiting width-thickness ratios λp from Table 2

of the code. If the width-thickness ratio of one or more compression elements

exceeds λp, but does not exceed λr, the section is Compact (Class 2). If the

width-thickness ratio of any element exceeds λr but does not exceed λs, the sec-

tion is Semi-Compact (Class 3). If the width-thickness ratio of any element ex-

ceed λs, the section is considered Slender (Class 4). The expressions of λp, λr,

and λs, as implemented in the program, are reported in Table 3-1 (IS 3.7.2, Ta-

ble 2).

The table uses the variables h, bf, tf, tw, b, t, D, d, and so on. The variables b, d,

D and t are explained in the respective figures inside the table. The variables

bf, tf, h, and tw are explained in Figure 3-1.

For unstiffened elements supported along only one edge parallel to the direc-

tion of the compression force, the width shall be taken as follows (IS Table 2,

Note 3):

(a) For flanges of I-shaped members and tees, the width b is the clear distance

between the lateral support and the free edge.

(b) For legs of angles and flanges of channels and zees, the width b is the full

nominal dimension.

fasteners or line of welds.

(d) For stems of tees, d is taken as the full nominal depth of the section.

Refer to Table 3-3 (IS Table 2) for the graphic representation of unstiffened el-

ement dimensions.

For stiffened (internal) elements supported along two edges parallel to the di-

rection of the compression force, the width shall be taken as follows (IS Table

2):

(a) For webs of rolled or formed sections, d is the clear distance between

flanges less the fillet or corner radius at each flange.

(b) For webs of built-up sections, d is the distance between adjacent lines of

fasteners or the clear distance between flanges when welds are used.

the clear distance between webs. For webs of rectangular HSS, d is the

clear distance between the flanges.

Table 3-3 Limiting Width-Thickness Ratios of Compression Elements for

Classification Sections

Section

Type

Description

of Element

Example

Width-

Thickness

Ratio,

( )

Limiting Width-Thickness Ratios for Compression

Element

Plastic

Class 1

( )

Compact

Class 2

( )

Semi-Compact

Class 3

( )

Doubly Symmetric I-Shape

Flexural

compression

of flanges of

rolled

I-Shapes

9.4ε 10.5ε 15.7ε

Flexural

compression

in flanges of

built-up

I-Shapes

8.4ε 9.4ε 13.6ε

Axial only

compression

in flanges of

rolled

I-Shapes

9.4ε 10.5ε 15.7ε

Axial only

compression

in flanges of

built-up

I-Shapes

8.4ε 9.4ε 13.6ε

Flexure in web

≥ 42ε

if r ≤ 0

105

if r > 0

105

1 1.5r

≥ 42ε

126

12r

≥ 42ε

Web in axial

only

compression

NA NA 42ε

Table 3-3 Limiting Width-Thickness Ratios of Compression Elements for

Classification Sections

Section

Type

Description

of Element

Example

Width-

Thickness

Ratio,

( )

Limiting Width-Thickness Ratios for Compression

Element

Plastic

Class 1

( )

Compact

Class 2

( )

Semi-Compact

Class 3

( )

Channel

Flexural

compression

in flanges

9.4ε 10.5ε 15.7ε

Axial only

compression

in flanges

9.4ε 10.5ε 15.7ε

Flexure in web

42ε 42ε 42ε

Web in axial

only

compression

42ε 42ε 42ε

Double Channel

Flexural

compression

in flanges

9.4ε 10.5ε 15.7ε

Axial only

compression

in flanges

9.4ε 10.5ε 15.7ε

Flexure in web

42ε 42ε 42ε

Web in axial

only

compression

42ε 42ε 42ε

Table 3-3 Limiting Width-Thickness Ratios of Compression Elements for

Classification Sections

Section

Type

Description

of Element

Example

Width-

Thickness

Ratio,

( )

Limiting Width-Thickness Ratios for Compression

Element

Plastic

Class 1

( )

Compact

Class 2

( )

Semi-Compact

Class 3

( )

Box

Flexural or

axial

compression

of flanges

under major

axis bending

29.3ε 33.5ε 42ε

Flexure in web

> 42ε

if r ≤ 0

105

if r > 0

105

1 1.5r

> 42ε

126

12r

> 42ε

T-Shape

Flexural or

axial

compression

in flanges

9.4ε 10.5ε 15.7ε

Compression

in stems

8.4ε 9.4ε 18.9ε

Double Angle

Any type of

compression

in leg

9.4ε 10.5ε 15.7ε

Any type of

compression

in leg

9.4ε 10.5ε 15.7ε

( )

bdt+

――― ――― 25ε

Angle

Flexural

compression

in any leg

9.4ε 10.5ε 15.7ε

Axial only

compression

in any leg

9.4ε 10.5ε 15.7ε

( )

bdt+

――― ――― 25ε

Table 3-3 Limiting Width-Thickness Ratios of Compression Elements for

Classification Sections

Section

Type

Description

of Element

Example

Width-

Thickness

Ratio,

( )

Limiting Width-Thickness Ratios for Compression

Element

Plastic

Class 1

( )

Compact

Class 2

( )

Semi-Compact

Class 3

( )

Pipe

Flexural

compression

42ε

52ε

146ε

Axial only

compression

――― ―――

88ε

Round

Bar

――― ――― ――― Assumed Compact

Rectan-

gular

――― ――― ――― Assumed Compact

General

―――

Assumed Compact

Section

――― ――― ――― Assumed Compact

Refer to Table 3-3 (IS Table 2) for the graphic representation of stiffened ele-

ment dimensions.

The various parameters used in calculating the width-to-thickness ratio limits

are defined as:

250 y

fε=

(IS Table 2 Notes)

( )

10wy

rdt f

= − γ

(IS Table 2 Notes)

20y

rAf

= − γ

(IS Table 2 Notes)

In classifying web slenderness of I-Shapes, Box, Channel, Double Channel,

and all other sections, it is assumed that there are no intermediate stiffeners.

Double Angles and Channels are conservatively assumed to be separated.

Stress check of Slender sections is beyond the scope of this program.

2, y

3, z3, z

IS 800:2007 : Axes Conventions

2-2 is the cross section axis

parallel to the webs, the

longer dimension of tubes,

the longer leg of single

angles, or the side by side

legs of double anges. This is

the same as the y-y axis.

3-3 is orthogonal to 2-2. This is

the same as the z-z axis.

b b 3t= −

h d 3t= −

PNA

2, y

3, z3, z

2, y

3, z3, z

IS 800:2007 : Axes Conventions

2-2 is the cross section axis

parallel to the webs, the

longer dimension of tubes,

the longer leg of single

angles, or the side by side

legs of double anges. This is

the same as the y-y axis.

2-2 is the cross section axis

parallel to the webs, the

longer dimension of tubes,

the longer leg of single

angles, or the side by side

legs of double anges. This is

the same as the y-y axis.

3-3 is orthogonal to 2-2. This is

the same as the z-z axis.

3-3 is orthogonal to 2-2. This is

the same as the z-z axis.

b b 3t= −

h d 3t= −

b b 3t= −

h d 3t= −

PNA

Figure 3-1 IS 800:2007 Definition of Geometric Properties

3.7 Calculation of Factored Forces and Moments

The factored member loads that are calculated for each load combination are

P, Mz, My, Vy, and Vz, corresponding to factored values of the axial force, the

major and minor moments, and shears respectively. These factored loads are

calculated at each of the previously defined stations.

For slender compression members, the code recommends the use of a second

order frame analysis, also called a P-∆ analysis, which includes the effect of

sway deflections on the axial loads and moments in a frame. For an adequate

and rational analysis, realistic moment curvature or moment rotation relation-

ships should be used to provide accurate values of deflections and forces. The

analysis also should include the effect of foundation rotation and sustained

loads. Because of the complexity in the general second order analysis of

frames, the code provides an approximate design method that takes into

account the “amplification” due to lateral deflections in columns (IS 4.4, 9.3

Annex B).

Hence, when using the “Indian IS 800:2007” code, it is recommended that the

user include P-Delta analysis, including consideration of method, tolerances, P-

Delta load combinations and so on. With this analysis, the program can capture

the lateral drift effect, i.e., the global effect or P-∆ effect, very nicely. But the

program does not capture the local effect (P-δ effect) to its entirety because

most often the column members are not meshed. To capture the local effects in

columns, the program uses the approximate formula for amplified design

moments as specified in the code (IS 9.3). Two major parameters in calculating

the amplified design moments are the effective length factors for major and

minor axis bending. The effective length factors for columns are computed

using a code-specified procedure (IS 7.2.2, Annex D). If P-∆ analysis is not

selected, the program calculates effective length factors, K, assuming the frame

is a sway frame (sway unrestrained) (IS Annex D, Figure 28). However, if the

P-∆ analysis is selected, the program assumes the member is prevented from

further sway and assumes that the frame can be considered non-sway where

K < 1 (IS Annex D, Figure 27). For more information on P-∆ and P-δ effects,

please refer to Chapter 2 “Second Order P-Delta Effects.” See “Effective

Length Factors (K)” also in Chapter 2 concerning the determination of K

factors.

3.8 Calculation of Factored Strengths

The design strengths in compression, tension, bending, and shear are computed

for Plastic (Class 1), Compact (Class 2), and Semi-Compact (Class 3) sections

in accordance with the text in the following sections. The design flexural

strength for all shapes of sections are calculated based on their principal axes

of bending. For the Rectangular, I-Shape, Box, Channel, Double Channel, Cir-

cular, Pipe, T-Shape, and Double Angle sections, the principal axes coincide

with their geometric axes. For the Single Angle sections, the principal axes are

determined and all computations except shear are based on that.

For all sections, the design shear strengths are calculated for directions aligned

with the geometric axes, which typically coincide with the principal axes.

Again, the exception is the Single Angle section.

If the user specifies nonzero design strengths for one or more of the mem-

bers on the Steel Frame Overwrites form, those values will override the

calculated values for those members. The specified capacities should be

based on the principal axes of bending for flexure and on the geometric

axes for shear.

3.8.1 Design Tensile Strength

This section applies to the members subject to axial tension.

The factored design tension, T, in the members shall satisfy the following

requirements:

1.0

T≤

(IS 6.1)

where

Td = design strength of the member.

The design strength of a member under axial tension, Td is the lowest of the de-

sign strength due to yielding of the gross section, Tdg and the rupture strength

of the critical section Tdn.

Td = min(Tdg, Tdn) (IS 6.1)

The design strength of members under axial tension, Tdg as governed by the

yielding gross section, is given by:

g gy m

T Af

= γ

(IS 6.2)

fy = yield stress of the material,

Ag = gross area of the cross-section, and

γm0 = partial safety factor for failure in tension by yielding (IS Table 5)

The design strength in tension of the section, Tdn, as governed by rupture of net

cross-sectional area, An, is given by

0.9

dn n u m

T Af= γ

(IS 6.3)

where

An = net effective area of the member

fu = ultimate stress of the material, and

γm1 = partial safety factor for failure at ultimate stress (IS Table 5)

The values of Ag and An are defined as follows:

The gross cross-section area, A, is based on nominal dimensions, ignoring fas-

tener holes and splice materials, and accounting for larger openings (IS 6.2).

The net effective cross-section area, An, is defined as the gross cross-section ar-

ea, A, minus fastener holes and other openings. The net effective area, An, is as-

sumed to be equal to the gross cross-sectional area, Ag, by default. For mem-

bers that are connected with welds or members with holes, the

ratio

must be modified using the steel frame design Overwrites to account for the ef-

fective area.

3.8.2 Design Compressive Strength

The design compressive strength is taken as the minimum of the two limit

states: Flexural Buckling; and Torsional and Flexural-Torsional Buckling.

3.8.2.1 Flexural Buckling Limit State

The design compressive strength, Pd, of a member is given by:

Pd = Ae fcd (IS 7.1.2)

where,

Ae = effective section area; for Class I, Class 2, and Class 3 cross-

sections, it is taken as the gross sectional area (IS 7.3.2) and

fcd = design compressive stress.

The design compressive stress, fcd, or axially loaded compression members is

calculated using the following equation:

000

0.5

cd ym ym

f ff

= =χγ≤ γ



φ+ φ −λ



(IS 7.1.2.1)

where

φ =

( )

[ ]

0.5 1 0.2+α λ− +λ

(IS 7.1.2.1)

λ = non-dimensional effective slenderness ratio

( )

y cc y KL

ff f E

= π

(IS 7.1.2.1)

fcc = Euler buckling stress =

( )

KLr

(IS 7.1.2.1)

where

KL r

= effective slenderness ratio or ratio of effective length,

KL, to appropriate radius of gyration, r,

α = imperfection factor given in IS Table 7

χ = stress reduction factor

( )

0.5



φ+ φ −λ



(IS 7.1.2)

γm0 = partial safety factor for material strength.

The effective slenderness ratio,

KL r

, is given by:

33 33 22 22

33 22

max ,

KL K L K L

r rr



=



For all sections except Single Angles, the principal radii of gyration r22 and r33

are used. For Single Angles, the minimum (principal) radius of gyration, rz, is

used instead of r22 and r33, conservatively, in computing

KL r

K33 and K22 are

two values of K2 for the major and minor axes of bending. K2 is the effective

length factor for actual (sway or nonsway) conditions.

K is the effective length factor for flexural buckling. It can assume two values:

K22 for buckling about the minor axis (y-y) and K33 for buckling about the ma-

jor axis (z-z). L is the unbraced length of the member. It also can assume two

values, L22 and L33, for buckling about minor axis (y-y) and major axis (z-z),

respectively. Please refer to Chapter 2 “Member Unsupported Length” and

“Effective Length Factors (K)” for more details on L and K.

The imperfection factor, α, is defined in Table 3-4 (IS 7.1.1, 7.1.2.1, Table 7)

based on the buckling class. The buckling class is defined in Table 3-5 (IS

7.1.2.2, Table 10) based on shapes, dimensional properties, and bending axis.

Table 3-4: Imperfection Factors (IS 7.1.1, 7.1.2.1, Table 7)

Buckling Class a b c d

Imperfection Factor, α 0.21 0.34 0.49 0.76

Table 3-5: Buckling Class of Cross-Section (IS 7.1.2.2, Table 10)

Section Shape Limits Axis

Buckling

Class

Rolled I-Sections

h/b > 1.2

tf ≤ 40 mm

Major

Minor

40 < t

≤ 100

Major

Minor

h/b ≤ 1.2

tf ≤ 100 mm

Major

Minor

tf > 100 mm

Major

Minor

Welded I-Sections

tf ≤ 40 mm

Major

Minor

tf > 40 mm

Major

Minor

Hollow Tube and Pipe Sections

hot rolled

any

Welded Box

b/tf > 30 or h/tw > 30

any

b/tf < 30 and h/tw < 30

any

Channel, Tee, Double Channel,

General, Solid Sections, Section

Designer

none any c

Angle and Double Angle Sections

none

any

3.8.2.2 Torsional and Flexural-Torsional Buckling

Torsion and Flexural-Torsional Buckling are currently not covered in Indian IS

800:2007 code. However, program incorporates the relevant clauses from

AISC 360-05 code to cover the torsion and flexural torsion buckling which are

important part of design.

The limit states of torsional and flexural-torsional buckling are ignored for

members with closed sections, such as Box and Pipe sections, solid sections

(Circular and Rectangular), General sections and sections created using the

Section Designer.

The design compressive strength, Pd, of a member with I, Box, Channel, Dou-

ble Channel, Double Angle, and Angle sections is given by:

Pd = Ae fcd (IS 7.1.2)

where,

Ae = effective sectional area

00cd ym ym

ff f=χγ≤ γ

(IS 7.1.2.1)

χ =

( )

0.5



φ+ φ −λ



(IS 7.1.2.1)

φ =

( )

[ ]

0.5 1 0.2

+α λ− +λ

(IS 7.1.2.1)

λ =

α = imperfection factor for minor axis bending

Fe is calculated from the following equations:

I-Shapes and Double Channel Sections

( )

222 33

F GJ II







= + 







(AISC E4-4)

Channel Sections

( )

33 33

e ez e ez

e ez

F F F FH

FHFF







= −−





 +



(AISC E4-5)

Double Angle and T-Shapes

( )

22 22

e ez e ez

e ez

F F F FH

FHFF







= −−





 +



(AISC E4-2)

Single Angle Sections with Equal Legs

( )

33 33

e ez e ez

e ez

F F F FH

FHFF







= −−









(AISC E4-5)

Single Angle Sections with Unequal Legs

Fe is the lowest root of the cubic equation.

( )( )

( )

( ) ( )

33 22 22 33

ee ee eez eee eee

FF FF FF FFF FFF

 

− − −−− −− =

 

 

(AISC E4-6)

In the preceding equations,

Cw is the warping constant, in6 (mm6)

x0, y0 are the coordinates of the shear center with respect to the centroid, x0 =

0 for Double Angle and T-Shaped members (y-axis symmetry)

2222 33

xy A

++ =

polar radius of gyration about the shear center

(AISC E4-7)

H =



−



(AISC E4-8)

33e

( )

33 33 33

KL r

(AISC E4-9)

22e

( )

22 22 22

KL r

(AISC E4-10)

( )

z LT

EC GJ Ar







(AISC E 4-11)

K22, K33 are effective length factors K2 in minor and major directions.

Kz is the effective length factor for torsional buckling, and it is taken

equal to KLTB in this program; it can be overwritten.

L22, L33 are effective lengths in the minor and major directions.

r22, r33 are the radii of gyration about the principal axes.

LLT is the effective length for torsional buckling, but it can be overwrit-

ten.

For Angle sections, the principal moment of inertia and radii of gyration are

used for computing Fe. Also, the maximum value of KL, i.e., max (K22L22,

K33L33), is used in place of K22L22 or K33 L33 in calculating Fe22 and Fe33 in this

case. The principal maximum value rmax is used for calculating Fe33 , and the

principal minimum value rmin is used in calculating Fe22.

3.8.3 Flexure Strength

The factored moment resistance in the major and minor directions is based on

the geometric shape of the section, the section classification for compactness,

and the unbraced length of the member. The bending strengths are evaluated in

accordance with the code as follows (IS 800:2007).

The program uses the minimum of the flexure strength, Md, computed from

Cross-Section Strength and Lateral-Torsional Buckling Strength (IS 8.2).

3.8.3.1 Cross-Sectional Strength

The cross-sectional flexural strengths of the member are calculated assuming

the member is laterally fully supported.

When the factored design shear force does not exceed 0.6 Vd, where Vd is the

design shear strength of the cross-section, the design bending strength, Md is

taken as:

1.2

d bpym eym

M Zf Zf=β γ≤ γ

(IS 8.2.1.2)

where

βb = 1.0 for plastic and compact sections,

for semi-compact sections,

Zp = plastic section modulus of the cross-section,

Ze = elastic section modulus of the cross-section,

fy = yield stress of the material,

γm0 = partial safety factor.

When the design shear force (factored), V exceeds 0.6Vd, where Vd is the design

shear strength of the cross-section, the design bending strength, Md is taken as

Md = Mdv (IS 8.2.1.3)

where

Mdv = design bending strength under high shear.

When the factored shear force is less than or equal to 0.6 times the design shear

strength (V ≤ 0.6 Vd), there is no reduction in moment capacity of the section

necessary (IS 9.2.1). When the factored shear force is high (V > 0.6 Vd), the

moment capacity of the section is reduced to Mdv which is calculated as follows

(IS 9.2.2):

(a) Plastic (Class 1) and Compact (Class 2) Sections

( )

1 1.2

dv d fd e y m

M M M Zf= −β +β ≤ γ

(IS 9.2.2(a))

where

( )

0 if 0.6

2 1 , if 0.6

VV VV

≤





β=

−>





(IS 9.2.2(a))

Md = plastic design moment of the whole section disregard-

ing high shear force effect (IS 8.2.1.2) considering web

buckling effects (IS 8.2.1.1),

V = factored applied shear force,

Vd = design shear strength as governed by web yielding or

web buckling (IS 8.4.1, 8.4.2),

Mfd = plastic design strength of the area of cross-section ex-

cluding the shear area, considering partial safety factor γm0,

Ze = elastic section modulus of the entire section.

Mfd is considered for I, Box, Channel, and Double Channel sec-

tions about the major axis bending and for only Box sections about

the minor axis bending. For all other cases, Mfd is conservatively

taken as zero.

(b) Semi-Compact (Class 3) Section

( )

dv d fd e y m

M M M Zf= −β +β ≤ γ

(IS 9.2.2(b))

where β, Md, V, Vd, Mfd, and Ze are the same as defined previously.

3.8.3.2 Lateral-Torsional Buckling Strength

The design bending strength of a laterally unsupported beam as governed by

lateral-torsional buckling is given by

Md = βbZp fbd (IS 8.2.2)

where

βb = 1.0 for Plastic (Class1) and Compact (Class 2) sections

for Semi-Compact (Class 3) sections,

= plastic section modulus and elastic section modulus with re-

spect to extreme compression fiber

fbd = design bending compressive stress, obtained as given in the

following

fbd =

0LT y m

fχγ

χLT = bending stress reduction factor to account for lateral-torsional

buckling, given by:

{ }

0.5

11χ= ≤



φ+φ−λ



LT LT LT

(IS 8.2.2)

( )

0.5 1 0.2

LT LT LT LT



φ = +α λ − +λ



(IS 8.2.2)

αLT = the imperfection parameter. It is given by:

= 0.21 for rolled steel section, and

= 0.49 for welded steel section.

The non-dimensional slenderness ratio, λ LT, is given by:

1.2

LT b p y cr e y cr

ZfM ZfMλ=β ≤

(IS 8.2.2)

where,

Mcr = elastic critical moment calculated in accordance with Annex E.

The elastic critical moment, Mcr, is based on gross cross-section properties and

taken as:

0.5



= +





yw LT t

cr LT y y

EI I L GI

LI EI

(IS Annex E, 8.2.2.1)

where Iy, Iw, and It are the minor axis inertia, warping constant, and torsion con-

stant, respectively; LLT is the effective unbraced length for the lateral-torsional

buckling mode, and C1 is defined as:

11.88 1.40 0.52 2.7C= − ψ+ ψ ≤

(EC3-1993 F1.1(6))

where

is the ratio of the smaller to the larger end moments. The value of C1 is

also taken as 1.0 if the unbraced length is overwritten. The value of C1 can be

overwritten on a member-by-member basis.

C1 should be taken as 1.0 for cantilevers. However, the program is unable to

detect whether the member is a cantilever. The user should overwrite C1 for

cantilevers. The program also defaults C1 to 1.0 if the minor unbraced length,

l22, is redefined to be more than the length of the member by the user or the

program, i.e., if the unbraced length is longer than the member length. The

Overwrites can be used to change the value of C1 for any member.

Here LLT is the effective unbraced length for the lateral-torsional buckling

mode.

LLT = KLTBLLTB

where KLTB is the effective length factor for the lateral-torsional buckling mode,

and LLTB is the unbraced length for the lateral-torsional buckling mode. For

more details on these two factors, please refer to Chapter 2 of this manual.

The lateral-torsional buckling resistance of Channels, Double Channels, Tees,

Angles, Double Angles, and I-sections is calculated as described previously.

Lateral-torsional buckling is not considered for Tubular, Box, or Solid sections.

For General or Section Designer sections, the lateral-torsional buckling re-

sistance is taken as the design elastic moment resistance.

3.8.4 Design Shear Strength

The factored shear strengths are calculated for shears along the geometric axes

for all sections. For I-Shape, Box, Channel, Double Channel, T-Shape, Double

Angle, Pipe, Circular, and Rectangular sections, the principal axes coincide

with their geometric axes. For Angle sections, principal axes do not coincide

with their geometric axes.

In calculating factored strength for shear, Vd, it is assumed that there is no in-

termediate stiffness used to enhance shear strength of a section (IS 8.4.2.2).

The design shear strength, Vd, is taken as

0d nm

VV= γ

(IS 8.4)

where the nominal shear strength of a cross section, Vn, may be governed by

plastic shear resistance (IS 8.4.1) or strength of the web, as governed by shear

buckling (IS 8.4.2).

3.8.4.1 Plastic Shear Resistance

The nominal plastic shear resistance under pure shear is given by:

Vn = Vp (IS 8.4.1)

where

v yw

(IS 8.4.1)

Av = shear area, and

fyw = yield strength of the web. (IS 8.4.1)

The shear area is calculated as given in the following (IS 8.4.1):

 I and Channel sections:

Major Axis Bending

Hot-Rolled — htw

Welded — dtw

Minor Axis Bending

Hot-Rolled or Welded — 2btf

 Rectangular Hollow Sections of Uniform Thickness

Loaded parallel to depth (h) —

()

Ah b h+

Loaded parallel to width (b) —

()

Ab b h+

 Circular Hollow Tubes of Uniform Thickness —

2Aπ

 Plates and Solid Bars — A

where,

A = cross-section area,

b = overall breadth of a tubular section, breadth of I-section flanges,

d = clear depth of the web between flanges,

h = overall depth of the section,

tf = thickness of the flange, and

tw = thickness of the web.

For all other sections, the equivalent elastic shear area is used.

3.8.4.2 Resistance to Shear Buckling

Resistance to shear buckling is verified when

67 ,

dt >ε

where

250 y

fε=

(IS 8.4.2.1).

The nominal shear strength, Vn, of webs as governed by buckling is evaluated

using the “simple post-critical method” assuming that the web has transverse

stiffeners at the supports. The nominal shear strength is given by:

Vn = Vcr, (IS 8.4.2.2)

where,

Vcr = shear force corresponding to web buckling,

= Avτb,

τb = shear stress corresponding to web buckling, determined as fol-

lows:

 when λw ≤ 0.8

b yw

τ=

(IS 8.4.2.2)

 when 0.8 < λw < 1.2

( )

1 0.8 0.8 3 ,

b w yw



τ= − λ−



(IS 8.4.2.2)

 when λw ≥ 1.2

( )

b yw w

fτ= λ

(IS 8.4.2.2)

λw = non-dimensional web slenderness ratio for shear buckling stress,

( )

τ,

yw cr e

(IS 8.4.2.2)

τcr,e = the elastic critical shear stress of the web,

( )

[ ]

12 1

−µ

(IS 8.4.2.2)

µ = Poisson’s ratio, and

Kv = 5.35 when transverse stiffeners are provided only at supports

()

4.0 5.35 cd+

for

1.0cd

()

5.35 4.0 cd+

for

1.0cd

≥

where c, d are the spacing of the transverse stiffeners and the depth

of the web, respectively. It is assumed that c is very large.

3.9 Design of Members for Combined Forces

Previous sections of this design manual address members subject to only one

type of force, namely axial tension, axial compression, flexure, or shear. This

section addresses the design of members subject to a combination of two or

more of the individual forces. In the calculation of the demand/capacity (D/C)

ratios, first, for each station along the length of the member, the actual member

force/moment components are calculated for each design combination. Then,

the corresponding capacities are calculated. Then, the D/C ratios are calculated

at each station for each member under the influence of each of the design com-

binations. The controlling D/C ratio is then obtained, along with the associated

station and design combination. A D/C ratio greater than the D/C ratio limit

(whose default value is 1.0) indicates exceeding a limit state.

During the design, the effect of the presence of bolts or welds is not consid-

ered.

3.9.1 Combined Axial Force and Bending Moment

Under combined axial force and bending moment, section strength as governed

by material failure and member strength as governed by buckling failure shall

be checked in accordance with IS 9.3.1 and IS 9.3.2, respectively.

3.9.1.1 Design for Cross-Section Strength

The combined effect of axial force and bending moments is checked in the

same way whether the axial force is a tensile force or a compression force.

There are minor exceptions that are noted in the relevant sections.

3.9.1.1.1 Plastic (Class 1) and Compact (Class 2) Cross-Sections

(a) For I, Rectangular Hollow, Circular Tube, and Solid Rectangular sec-

tions, the combined axial force (tension or compression) and bending

moment is checked by taking the following summation of the utilization

ratios for each force component as follows:

ndy ndz



+≤





αα

(IS 9.3.1.1(a))

In the equation 9.3.1.1(a), there are two basic ratios — major axis bend-

ing (z) and minor axis bending (y) — and two factors α1 and α2 which

determine the overall PMM ratio. The factors α1 and α2 in tern depend on

the axial (n) ratio. Since α1 and α2 are often more than one, the overall ra-

tio can be smaller than the individual component ratios when the compo-

nent ratios are less than one. In this case the program reports either of the

pure bending moment ratios or the axial ratio whichever governs as the

PMM ratio as follows:

ndy

M≤

(IS 9.3.1.1(ay))

ndz

M≤

(IS 9.3.1.1(az))

N≤

(IS 9.3.1.1(an))

where,

My, Mz = factored applied moments about the minor and major

axis of the cross-section, respectively,

Mndy, Mndz = design reduced flexural strength under combined axial

force and the respective uniaxial moment acting alone

(IS 9.3.1.2),

N = factored applied axial force (tension, T, or compression,

P),

Nd = design strength in tension, Td, as obtained from IS 6 or

in compression due to yielding given by

d gy m

N Af= γ

Mdy, Mdz = design strength under corresponding moment acting

alone (IS 8.2),

Ag = gross area of the cross-section,

γm0 = partial factor of safety in yielding, and

α1, α2 = constants as given in IS 9.3.1.1, Table 17, and taken as

follows:

– For I-sections and channels

α1 = 5n ≥ 1 (IS 9.3.1.1, Table 17)

α2 = 2 (IS 9.3.1.1, Table 17)

– For Rectangular Hollow sections

1 66 6

1 1 13

= ≤

−

(IS 9.3.1.1, Table 17)

1 66 6

1 1 13

= ≤

−

(IS 9.3.1.1, Table 17)

– For Circular Tube sections

12=

(IS 9.3.1.1, Table 17)

– For Solid Rectangular sections

1173 18. .n= +

(IS 9.3.1.1, Table 17)

2173 18. .n= +

(IS 9.3.1.1, Table 17)

In all of the preceding cases, n is taken as

(IS 9.3.1.1, Table 17)

Mndy and Mndz are computed as follows:

– For Solid Rectangular sections

Mndz =

()

−

(IS 9.3.1.2(a))

Mndy =

( )

Mn−

(IS 9.3.1.2(a))

– For Welded I-sections

1 05

ndz dz

MM .a

−



=

−



(IS 9.3.1.2 (b))

for

1 for

ndy

M , n a,

Mna

M , na

≤





=

−



−>





−







(IS 9.3.1.2 (b))

where,

−

= ≤

205

A bt

(IS 9.3.1.2 (b))

– For Rolled I-sections

( )

1 11 1

ndz dz dz

M .M n M= −≤

(IS 9.3.1.2 (c))

( )( )

if 0 2

156 1 06 if 02

ndy

dy dy

M , n .,

M. M nn . M, n .

≤





=− +≤ >





(IS 9.3.1.2 (c))

– For Hollow Rectangular sections:

1 05

ndz dz dz

MM M

−



= ≤



−



(IS 9.3.1.2(d))

1 05

ndy dy dy

MM M

−



= ≤



−



(IS 9.3.1.2(d))

where

−

= ≤

205

A bt

(IS 9.3.1.2(d))

−

= ≤

205

A ht

(IS 9.3.1.2(d))

– For Hollow Circular Tube sections:

( )

1 04 1

ndz dz dz

M .M n M= −≤

(IS 9.3.1.2(e))

( )

1 04 1

ndy dy dy

M .M n M= −≤

(IS 9.3.1.2(e))

In all of the preceding cases, n is taken as

, if is tensile

, if is compressive





= = 





(IS 9.3.1.2)

(b) For Tee sections, combined axial force and bending is conservatively

checked by taking a linear summation of the utilization ratios for each

force component as:

1.0

d dy dz

NM M

++≤

(IS 9.3.1.1(b))

However, for this case the maximum longitudinal stress at three extreme

points of the section are added with appropriate sign. That means that at

the two extreme points on the flange, all three terms are added algebrai-

cally, whereas at the tip of the web, the minor axis bending term be-

comes zero.

tion Designer sections, combined axial force and bending is conserva-

tively checked by taking a linear summation of the utilization ratios for

each force component as:

1.0

d dy dz

NM M

++≤

(IS 9.3.1.1(b))

The equation number reported in the output for the interaction equations in this

section is really the section number 9.3.1.1. There are two interaction equations

in this section of the code of which none of them are numbered in the code it-

self. So the program named the equations as 9.3.1.1(a) and 9.3.1.1(b) to distin-

guish between them. Moreover, the program named the interaction equations

9.3.1.1(az), 9.3.1.1(ay) and 9.3.1.1(an) while checking the component ratios.

3.9.1.1.2 Semi-Compact (Class 3) Cross-Sections

For all shapes, with the exception noted in the following text, the combined ax-

ial force and bending is conservatively checked by taking the linear summation

of the utilization ratios for each force component:

1.0

d dy dz

NM M

++≤

(IS 9.3.1.3)

For Doubly Symmetric sections, the preceding equation is a representation of

the code-specified equation given here:

f≤

(IS 9.3.1.3)

As an exception for Circular and Pipe sections, an SRSS (Square Root of Sum

of Squares) combination is made first of the two bending components before

adding the axial load component, instead of the single algebraic addition as

implied by the interaction equations given by IS 9.3.1.3. The resulting interac-

tion equation is given by the following:

1.0

d dy dz

NM M



+ +≤





(IS 9.3.1.3)

As an exception, for Tee sections, the terms are algebraically added for three

extreme points of the section. See the previous section of this manual for de-

tails.

3.9.1.2 Design for Overall Member Strength

The combined effect of axial compression and bending with special emphasis

to flexural and lateral-torsional buckling is checked using Section IS 9.3.2.2.

The combined effect of axial tension and bending is checked in accordance

with Sections IS 9.3.2.1 and IS 9.3.2.2, with the exception that the axial term is

ignored while checking in accordance with Section 9.3.2.2.

The program checks these equations assuming the section is prismatic. For

nonprismatic sections the same equations are used. However the cross-section

properties used are based on the section being checked. The user is advised to

check the appropriateness of this method.

3.9.1.2.1 Sections Under Flexure and Axial Compression

The combined effect of axial compression and bending with special emphasis

to flexural and lateral-torsional buckling is checked by calculating the utiliza-

tion ratios based on the following two interaction equations:

1.0

my y z

y LT

dy dy dz

CM M

PKK

PM M

+ +≤

(IS 9.3.2.2(a))

0.6 1.0

my y mz z

dz dy dz

CM CM

PKK

P MM

+ +≤

(IS 9.3.2.2(b))

where,

Cmy, Cmz = equivalent uniform moment factor in accordance with IS

Table 18,

P = applied axial compression under factored load,

My, Mz = maximum factored applied bending moments about the y-

and z-axis of the member, respectively,

Pdy, Pdz = design strength under axial compression as governed by

buckling about the minor (y) and major (z) axis, respectively,

Mdy, Mdz = design bending strength about the y (minor) or z (major) axis

considering laterally unsupported length of the cross-section

(IS Section 8),

( )

1 0.2 1 0.8

yyy y

K nn= +λ− ≤ +

(IS 9.3.2.2)

( )

1 0.2 1 0.8

zzz z

K nn= +λ− ≤ +

(IS 9.3.2.2)

( ) ( )

0.1 0.1

0.25 0.25

LT y y

LT mLT mLT

KCC

=− ≥−

−−

(IS 9.3.2.2)

where,

ny, nz = ratio of actual applied axial force to the design axial strength

for buckling about the y and z axis, respectively, and

λ= π

(IS 7.1.2.1)

λ= π

(IS 7.1.2.1)

CmLT = equivalent uniform moment factor for lateral-torsional

buckling in accordance with IS Table 18 corresponding to

the actual moment gradient between lateral supports against

torsional deformation in the critical region under considera-

tion.

The equation number reported in the output for the interaction equations in this

section is really the section number 9.3.2.2. There are two interaction equations

in this section of the code of which none of them are numbered in the code it-

self. So the program named the equations as 9.3.2.2(a) and 9.3.2.2(b) to distin-

guish between them.

As an exception, for Circular and Pipe sections, an SRSS (Square Root of Sum

of Squares) combination is made first of the two bending components before

addition of the axial load component instead of simple algebraic addition as

implied by the equation given previously.

The Cmy, Cmz, and CmLT factors are the equivalent uniform moment factor for

minor bending, major bending, and lateral-torsional buckling mode and are

related to the distribution of moment over the braced segment. They are

calculated depending on the loading condition and moment diagram based on

Table 3-6 (IS Table 18, 9.3.2.2). All of the factors are calculated in the same

way, except that appropriate bending axis and bracing direction are used. See

Table 3-6 for details.

Table 3-6 Equivalent Uniform Moment Factor (IS Table 18, 9.3.2.2)

Bending Moment Diagram

Range

Case

Cmy, Cmz, CmLT

Two or More

Concentrated Loads or

Uniform Load

Single Concentrated

Load On Segment

MψM

Linear moment diagram

− 1 ≤ ψ ≤ 1 (a) 0.6 + 0.4ψ ≥ 0.4

ψM

s sh

MMα=

ψM

s sh

MMα=

End moment dominating

≥

0 ≤ αs ≤ 1 − 1 ≤ ψ ≤ 1 (b) 0.2 + 0.8αs ≥ 0.4 0.2 + 0.8αs ≥ 0.4

− 1 ≤ αs ≤ 0

0 ≤ ψ ≤ 1 (c) 0.1 − 0.8αs ≥ 0.4 − 0.8αs ≥ 0.4

− 1 ≤ ψ ≤ 0 (d) 0.1 (1 − ψ) − 0.8αs

≥ 0.4

0.2 (− ψ) − 0.8αs

≥ 0.4

h hs

MMα=

ψMh

h hs

MMα=

ψMh

Span moment dominating

≥

0 ≤ αh ≤ 1 − 1 ≤ ψ ≤ 1 (e) 0.95 − 0.05αh 0.90 + 0.10αh

− 1 ≤ αh ≤ 0

0 ≤ ψ ≤ 1 (f) 0.95 + 0.05αh 0.90 + 0.10αh

− 1 ≤ ψ ≤ 0 (g) 0.95 + 0.05αh(1+ 2ψ) 0.90 + 0.1αh(1+ 2ψ)

For members with sway buckling mode, the equivalent uniform moment factor Cmy = Cmz = 0.9

, C

z, C

mLT

are obtained according to the bending moment diagram between the relevant braced point.

Moment Factor Bending Axis Points Braced in Direction

Cmz z-z y-y

Cmy y-y z-z

CmLT z-z z-z

3.9.1.2.2 Sections Under Flexure and Axial Tension

The combined effect of axial tension and bending with special emphasis to

flexural and lateral-torsional buckling is checked by calculating the utilization

ratios based on the following three interaction equations:

1.0

d ec dy dz

MZ M M

−ψ + + ≤

(IS 9.3.2.1)

1.0

my y z

y LT

dy dz

CM M

+≤

(IS 9.3.2.2(a))

0.6 1.0

my y z

dy dz

CM M

+≤

(IS 9.3.2.2(b))

where,

T = factored tensile force,

A = area of the cross-section,

Zec = elastic section modulus of the section with respect to the extreme

compression fiber,

ψ = 0.8, taken conservatively assuming M can vary independently,

and all other parameters have been described in the previous section.

The equation number reported in the output for the last two of the interaction

equations in this section is really the section number 9.3.2.2. There are two in-

teraction equations in this section of the code of which none of them are num-

bered in the code itself. So the program named the equations as 9.3.2.2(a) and

9.3.2.2(b) to distinguish between them. These two equations strictly applies to

cases with axial compression and bending. However, they are still used in the

case of axial tension and flexure to check flexural buckling mode. In this case

the advantage of axial tension is ignored.

As an exception, for Circular and Pipe sections, an SRSS (Square Root of Sum

of Squares) combination is made first of the two bending components before

addition of the axial load component instead of simple algebraic addition as

implied by the equation given previously.

3.9.2 Combined Axial Force, Bending Moment, and Shear Force

The combined effect of axial force, shear force, and bending moment is

checked in the same way as described in Section 3.9.1 “Combined Axial Force

and Bending Moments,” with one exception. The exception is that moment ca-

pacity may be reduced depending on the value of shear force (IS 9.2.1, 9.2.2).

This includes checking for cross-section strength (IS 9.3.1) only. The overall

member strength (IS 9.3.2) is checked without consideration of the shear force.

When the factored shear force is less than or equal to 0.6 times the design shear

strength (V ≤ 0.6 Vd), there is no reduction in moment capacity of the section

necessary (IS 9.2.1). When the factored shear force is high (V > 0.6 Vd), the

moment capacity of the section is reduced to Mdv, which is calculated as de-

scribed in Section 3.8.3.1 (IS 9.2.2).

3.9.3 Shear Stresses

From the factored shear force values and the factored shear strength values at

each station, for each of the load combinations, D/C ratios for shear in major

and minor directions are produced as follows:

1.0≤

(IS 8.4)

1.0≤

(IS 8.4)

3.10 Checking the Maximum Effective Slenderness Ratio of a

Member

The maximum effective slenderness ratio, KL/r values of a beam, strut or ten-

sion member shall not exceed those given in Table 3-7 (IS 3.8 Table 3). KL is

the effective length of the member, and r is the appropriate radius of gyration.

33 33 22 22

33 22

max , .

Kl Kl

r rr



=



For all sections except Single Angles, the principal radii of gyration r22 and r33

are used. For Single Angles, the minimum (principal) radius of gyration, rz , is

used instead of r22 and r33 , conservatively, in computing

.Kl r

K33 and K22 are

two values of K2 for the major and minor axes of bending.

Table 3-7 Maximum Values of Effective Slenderness Ratios (IS 3.8, Table 3)

SI No. Member

Maximum

Effective

Slenderness

Ratio (KL/r)

i) A member carrying compressive loads resulting from dead loads

and imposed loads 180

ii) A member subjected to compression forces resulting from a com-

bination with wind/earthquake actions only, provided the defor-

mation of such member does not adversely affect the stress in any

part of the structure.

250

iii) Compression flange of a beam against lateral-torsional buckling. 300

iv) Members always under tension 400

Chapter 4

Special Seismic Provisions

This chapter provides a detailed description of the algorithms related to seismic

provisions in the design/check of structures in accordance with the “IS

800:2007 – Indian Standard: General Construction in Steel – Code of Practice”

(IS 2007). The implementation covers load combinations from “IS 800:2007,”

which are described in Section 4.4 Design Special Load Combinations in this

chapter. The loading based on "IS 1893:2002" and “IS 875:1987” has been

described in a separate document entitled “CSI Lateral Loads Manual” (IS

2007; CSI 2007).

For referring to pertinent sections of the corresponding code, a unique prefix is

assigned for each code.



Reference to the IS 800:2007 code is identified with the prefix “IS.”



Reference to the IS 1893 (Part 1):2002 code is identified with the prefix “IS

1893.”

4.1 Design Preferences

The steel frame design Preferences are basic assignments that apply to all of

the steel frame members. The Preferences have been described previously in

4 - 1

Steel Frame Design CSA S16-09

the relevant section of Chapter 3. Table 3-1 lists the steel frame design

Preferences. The following steel frame design Preferences are relevant to the

special seismic provisions.

 Importance Factor

 Seismic Zone

 Ignore Seismic Code?

 Ignore Special Seismic Load?

 Is Doubler Plate Plug Welded?

4.2 Overwrites

The steel frame design Overwrites are basic assignments that apply only to

those elements to which they are assigned. The overwrites have been described

previously in the relevant section of Chapter 3. Table 3-2 lists the steel frame

design Overwrites. The following steel frame design overwrites are relevant to

the special seismic provisions.

 Frame Type

4.3 Supported Framing Types

The code now recognizes the types of framing systems identified in the table

on the following page (IS 12). With regard to those framing types, the program

has implemented specifications for all of the types of framing systems listed,

except EBF.

By default in the program, the frame type is taken as SMF. However, the

default frame type can be changed in the Preferences for all frames or in the

Overwrites on a member-by-member basis (Chapter 3). If a frame type

Preference is revised in an existing model, the revised frame type does not

apply to frames that have already been assigned a frame type through the

Overwrites; the revised Preference applies only to new frame members added

to the model after the Preference change and to the old frame members that

were not assigned a frame type though the Overwrites.

4 - 2 Overwrites

Chapter 4 - Special Seismic Provisions

Framing Type References

SMF (Special Moment Frame) IS 12.11

OMF (Ordinary Moment Frame) IS 12.10

SCBF (Special Concentrically Braced Frame) IS 12.7

OCBF (Ordinary Concentrically Braced Frame) IS 12.8

EBF ( Eccentrically Braced Frame)* IS 12.9

Secondary or Gravity only IS 12.1

*No special provision for EBF is programmed.

4.4 Design Special Load Combinations

The program creates the default design load combinations based on the

specification of the code. The default combinations have been described in

"Design Loading Combinations" in Chapter 3. Additional information may be

found in "Design Load Combinations" in Chapter 2. The user may change the

default load combinations if the governing code is different.

The program automatically considers seismic load effects, including

overstrength factors (IS 12.2.3), as special load combinations that are created

automatically from each load combination involving seismic loads. In that

case, the earthquake force is represented by 2.5E.

The special seismic combinations are

1.2DL + 0.5LL ± 2.5EL (IS 12.2.3(a))

0.9DL ± 2.5EL (IS 12.2.3(b))

4.5 Special Check for Column Strength

When

in columns due to a prescribed loading combination is greater

than 0.4, the axial compressive and tensile strengths are checked in the absence

of any applied moment and shear for the amplified seismic load combinations

(IS 12.5.1.1).

Design Special Load Combinations 4 - 3

Steel Frame Design CSA S16-09

1.2DL + 1.0LL ± 2.5EL (IS 12.2.3(a))

0.9DL ± 2.5EL (IS 12.2.3(b))

The preceding load combinations are used to calculate axial force only because

other forces and moments are ignored. This axial capacity check is in addition

to regular strength checks for the regularly specified load combinations (IS

12.5).

Those combinations are internal to the program. The user does NOT need to

create additional load combinations for such load combinations. The special

circumstances for which these load combinations are additionally checked are

described later in this chapter, as appropriate. The special loading combination

factors are applied directly to the load cases. It is assumed that any required

scaling (such as may be required to scale response spectra results) has already

been applied to the load cases.

If the overwrite item "Ignore Special Seismic Load?" is set to yes, the

preceding check will not be performed.

4.6 Member Design

This section describes the special requirements for designing a member. The

section has been divided into subsections for each framing type.

4.6.1 15BOrdinary Concentrically Braced Frames (OCBF)

For this framing system, the following additional requirements are checked or

reported (IS 12.7).

 OCBF shall not be used in Seismic Zones IV and V and for buildings with

an Importance Factor greater than 1 (I > 1) in Seismic Zone III.

 When

in columns due to prescribed loading combinations without

consideration of amplified seismic load is greater than 0.4, the axial com-

pressive and tensile strengths are checked in the absence of any applied

moment and shear for the special seismic load combinations as described

4 - 4 Member Design

Chapter 4 - Special Seismic Provisions

previously in the "Special Check for Column Strength" section of this

manual (IS 12.5.1).

 All brace members are checked to be Plastic (Class 1), Compact (Class 2)

or Semi-Compact (Class 3), but not Slender (Class 4) in accordance with

Table 3-3 (IS 12.7.2.4; 3.7.2, Table 2). If this criterion is not satisfied, the

program issues an error message.

 The maximum

/Kl r

ratio of the braces is checked not to exceed 120 (IS

12.7.2.1). If this criterion is not met, an error message is reported in the

output.

 The required compressive strength of braces shall not exceed 0.8 times Pd

(IS 12.7.2.2). If this criterion is not met, an error message is reported in the

output.

4.6.2 4BSpecial Concentrically Braced Frames (SCBF)

For this framing system, the following additional requirements are checked or

reported (IS 12.8).

 SCBF may be used in any seismic zone and for any bending irrespective of

the value of the importance factor (IS 12.8.1.1).

 When

in columns due to prescribed loading combinations without

consideration of amplified seismic load is greater than 0.4, the axial com-

pressive and tensile strengths are checked in the absence of any applied mo-

ment and shear for the special seismic load combinations as described previ-

ously in the "Special Check for Column Strength" section of this manual (IS

12.5.1).

 All column and brace members are checked to be Plastic (Class 1) in ac-

cordance with to Table 3-3 (IS 12.8.4.1, 12.8.2.5). If this criterion is not sat-

isfied, the program issues an error message.

 The bracing member is designed such that gross area yielding governs over

the net area rupture. This puts a limit on the net area of the gross area ratio

(IS 12.8.2.7). If this criterion is not satisfied, the program issues an error

message.

Member Design 4 - 5

Steel Frame Design CSA S16-09

 The maximum

Kl r

ratio of the braces is checked not to exceed 160 (IS

12.8.2.2). If this criterion is not satisfied, the program issues an error mes-

sage.

4.6.3 Eccentrically Braced Frames (EBF)

The code does not give any direct specification for this framing type. It rather

refers to specialist literature. The program does not check any special

requirement for the framing type.

4.6.4 12BOrdinary Moment Frames (OMF)

For this framing system, the following additional requirement is checked and

reported (AISC SEISMIC 11).

 OMF can not be used in seismic zones IV and V irrespective of the value of

the importance factor and in seismic zone III for buildings with an im-

portance factor greater than unity (I > 1) (IS 12.10.1.1).

 When

in columns due to prescribed loading combinations without

consideration of amplified seismic load is greater than 0.4, the axial com-

pressive and tensile strengths are checked in the absence of any applied mo-

ment and shear for the special seismic load combinations as described previ-

ously in the "Special Check for Column Strength" section of this chapter (IS

12.5.1).

4.6.5 10BSpecial Moment Frames (SMF)

For this framing system, the following additional requirements are checked or

reported (IS 12.11).

 This framing is applicable to any seismic zone and for any importance factor

(IS 12.11.1.2).

 When

in columns due to prescribed loading combinations without

consideration of amplified seismic load is greater than 0.4, the axial com-

pressive and tensile strengths are checked in absence of any applied moment

4 - 6 Member Design

Chapter 4 - Special Seismic Provisions

and shear for the special seismic load combination as described previously in

the "Special Check for Column Strength" section of this chapter (IS 12.5.1).

 All beams and columns are required to be Plastic (Class 1) or Compact

(Class 2) (IS 12.11.3.1). If this criterion is not satisfied, the program issues

an error message.

4.6.6 Secondary (Non-Seismic)

No special consideration for this type of framing system is needed.

4.7 Joint Design

When checking for seismic load, the structural joints are checked and designed

for the following.

 Check the requirement of continuity plate and determination of its area

 Check the requirement of doubler plate and determination of its thickness

 Check the ratio of beam flexural strength to column flexural strength

 Report the beam connection shear

 Report the brace connection force

4.7.1 20BDesign of Continuity Plates

In a plan view of a beam-column connection, a steel beam can frame into a

column in the following ways.

 The steel beam frames in a direction parallel to the column major direction,

i.e., the beam frames into the column flange.

 The steel beam frames in a direction parallel to the column minor direc-

tion, i.e., the beam frames into the column web.

Joint Design 4 - 7

Steel Frame Design CSA S16-09

 The steel beam frames in a direction that is at an angle to both of the prin-

cipal axes of the column, i.e., the beam frames partially into the column

web and partially into the column flange.

To achieve a proper beam-column moment connection strength, continuity

plates such as shown in Figure 2.3 of Chapter 2 are usually placed on the

column, in line with the top and bottom flanges of the beam, to transfer the

compression and tension flange forces of the beam into the column. For

connection conditions described by the first bullet, where the beam frames into

the flange of the column, such continuity plates are not always needed. The

requirement depends on the magnitude of the beam-flange force and the

properties of the column. This is the condition that the program investigates.

Columns of I Sections only are investigated. The program evaluates the

continuity plate requirements for each of the beams that frame into the column

flange (i.e., parallel to the column major direction) and reports the maximum

continuity plate area that is needed for each beam flange. The continuity plate

requirements are evaluated for moment frames (OMF, SMF) only. No check is

made for braced frames (OCBE, SCBF, EBF).

4.7.2 21BDesign of Doubler Plates

One aspect of the design of a steel framing system is an evaluation of the shear

forces that exist in the region of the beam-column intersection known as the

panel zone.

Shear stresses seldom control the design of a beam or column member.

However, in a Moment-Resisting frame, the shear stress in the beam-column

joint can be critical, especially in framing systems when the column is

subjected to major direction bending and the joint shear forces are resisted by

the web of the column. In minor direction bending, the joint shear is carried by

the column flanges, in which case the shear stresses are seldom critical, and

this condition is therefore not investigated by the program.

Shear stresses in the panel zone, due to major direction bending in the column,

may require additional plates to be welded onto the column web, depending on

the loading and the geometry of the steel beams that frame into the column,

either along the column major direction or at an angle so that the beams have

components along the column major direction. See Figure 2-3 of Chapter 2.

The program investigates such situations and reports the thickness of any

4 - 8 Joint Design

Chapter 4 - Special Seismic Provisions

required doubler plates. Only columns with I Shapes are investigated for

doubler plate requirements. Also doubler plate requirements are evaluated for

moment frames (OMF, SMF) only. No check is made for braced frames

(OCBF, SCBF, EBF).

The program calculates the required thickness of doubler plates using the

following algorithms. The shear force in the panel zone is given by

cos .

nbn n

nn fn

= −

−

∑

The available strength of the web panel zone for the limit state of shear

yielding is determined as Vd using the same procedure as described in Section

3.8.4 of this manual “Design Shear Strength.” There is an exception that Kv is

based on the assumption that the transverse stiffener spacing, c, is equal to the

center-to-center flange distance of the beam, and the panel depth is equal to the

depth of the column.

c = db − tf

d = dc

With this assumption, Kv, τcr,e, λw, and τb are calculated. Then Vd is taken as

Vn = tb dctwc (IS 8.4.2.2)

If shear buckling does not control, τb becomes equal to

(IS 8.4.1).

By using

Vγ

the required column panel zone thickness

is found

as follows.

0pm

=τ

The extra thickness, or the required thickness of the doubler plate is given as

follows:

= −

dp p w

t t t,

where,

Joint Design 4 - 9

Steel Frame Design CSA S16-09

= Column and doubler plate yield stress

= Required column panel zone thickness

= Flange thickness of

-th beam

= Required doubler plate thickness

= Column flange thickness

= Column web thickness

= Required panel zone shear capacity

= Column shear in column above

= Number of beams connecting to column

= Overall depth of

-th beam connecting to column

= Angle between

-th beam and column major direction

= Overall depth of column

= Factored beam moment from corresponding loading combination

= Nominal shear strength of panel

The largest calculated value of

, calculated for any of the load combinations

based on the factored beam moments and factored column axial loads, is

reported.

Doubler plate requirements for seismic design are evaluated for SMF only. No

further check/design is performed for other types of frames.

 For SMF, the panel zone doubler plate requirements that are reported will

develop at least the beam moments equal to the expected plastic moment

capacity of the beam

( )

1.2 ,

or beam moments due to specified load

combinations involving seismic load (IS 12.11.2.2). For seismic design,

4 - 10 Joint Design

Chapter 4 - Special Seismic Provisions

is calculated using the equation given previously, except that

is taken

as 1.2

33yp

(IS 12.11.2.1). All other calculations follow the same

procedure as given previously.

 For SMF, the program checks the following panel zone column web thick-

ness requirement:

( ) ( )

c fc b fb

dt dt

t− +−

≥

(IS 12.11.2.4)

Here,

is taken as

wc dp

when the doubler plate is plug welded to prevent

local buckling. In such cases,

is increased if necessary to meet this

criterion. If the doubler plate is not plug welded to the web,

is taken as

and also as

for checking both plates. If

cannot satisfy the criteria,

then a failure condition is declared. If

does not satisfy this criterion, then

its value is increased to meet the criterion. If the check is not satisfied, it is

noted in the output.

4.7.3 22BWeak Beam Strong Column Measure

Only for Special Moment Frames (SMF) the code requires that the sum of

column flexure strengths at a joint should be more than 1.2 times the sum of

beam flexure strengths (IS 12.11.3.2).

1.2

M≥

∑

(IS 12.11.3.2)

where

∑

= sum of the moment capacity in the column above and below

the beam centerline

∑

= sum of the moment capacity in the beam at the intersection of

the beam and the column centerlines

Joint Design 4 - 11

Steel Frame Design CSA S16-09

To facilitate the review of the strong column weak beam criterion, the program

will report a beam-column plastic moment capacity ratio for every joint in the

structure.

For the major direction of any column (top end), the beam-to-column-strength

ratio is obtained as

1.2 cos

pbn n

maj

pcax pcbx

RMM

∗

∗∗

∑

(IS 12.11.3.2)

For the minor direction of any column, the beam-to-column-strength ratio is

obtained as

1.2 sin

pbn n

maj

pcay pcby

RMM

∗

∗∗

= ,

∑

(IS 12.11.3.2)

where,

maj

= Plastic moment capacity ratios, in the major directions of the

column

min

= Plastic moment capacity ratios, in the minor directions of the

column

∗

pbn

= Plastic moment capacity of

-thn

beam connecting to the col-

umn

= Angle between the

-thn

beam and the column major direc-

tion

∗

pcax y

= Major and minor plastic moment capacities, reduced for axial

force effects, of column above story level

∗

,pcbx y

= Major and minor plastic moment capacities, reduced for axial

force effects, of column below story level

4 - 12 Joint Design

Chapter 4 - Special Seismic Provisions

= Number of beams connecting to the column

The plastic moment capacities of the columns are reduced for axial force

effects and are taken as

pc c yc

M ZF A

∗



= −





The plastic moment capacities of the beams are amplified for taking the beam

moment capacity at the centerline of the column, rather than at the face of the

column, as

∗

pb yb b mv

M FZf

where,

= Plastic modulus of beam

= Plastic modulus of column

= Yield stress of beam material

= Yield stress of column material

= Axial compression force in a column for a given load

combination

= Gross area of the column

= The moment amplification factor. It is taken as the ratio of beam

moment at the centerline of column to the moment of the column

face. Factor

is taken as follows:

where,

= Depth of column section, and

= clear span length of the beam.

Joint Design 4 - 13

Steel Frame Design CSA S16-09

For the preceding calculations, the section of the column above is taken to be

the same as the section of the column below, assuming that the column splice

will be located some distance above the story level.

4.7.4 23BEvaluation of Beam Connection Shears

For each steel beam in the structure, the program will report the maximum

major shears at each end of the beam for the design of the beam shear

connections. The beam connection shears reported are the maxima of the

factored shears obtained from the loading combinations.

For special seismic design, the beam connection shears are not taken less than

the following special values for different types of framing. The special seismic

requirements additionally checked by the program are dependent on the type of

framing used.

 For SMF, the beam connection shear is taken as the maximum of those from

regular load combinations and those required for the development of full

plastic moment capacity of the beam. The shear strength need not exceed the

required value corresponding to the special load combination in IS 12.2.3

with amplified earthquake load. The connection shear for the development of

the full plastic moment capacity of the beam is as follows:

1.2 1.2 0.5

DL LL

V VV

= ++

(IS 12.11.2.2)

where,

= Shear force corresponding to END I or END J of the beam

= 0 if the beam ends are pinned, or for a cantilever beam

= 1 if one end of the beam is pinned

= 2 if no ends of the beam are pinned

= Plastic moment capacity of beam

= Clear length of the beam

4 - 14 Joint Design

Chapter 4 - Special Seismic Provisions

= Absolute maximum of the calculated beam shears at the

corresponding beam ends from the factored dead load only

= Absolute maximum of the calculated beam shears at the

corresponding beam ends from the factored live load only

 For OMF, the beam connection shear is taken as the maximum of the two

values: (a) maximum shear from the load combinations and (b) maximum

shear based on beam moment capacity of the beam.

The maximum shear from the load combinations is determined from all of

the regular load combinations but not from the amplified seismic load

combinations (IS 12.2.3).

The maximum shear based on beam moment capacity is calculated for any

load combination involving seismic load by replacing the seismic effect on

shear force with the capacity shear as follows:

1.2 pb

u DL LL

V VV

= ++

(IS 12.10.2.1)

All parameters in the preceding equation have been described previously in

this section. The moment connection is assumed to be rigid.

 For SCBF the beam connection shear is taken as the maximum of those from

the regular load combination.

 For OCBF the beam connection shear is taken as the maximum of those from

the regular load combinations.

 For EBF, the beam connection shear is taken as the maximum of those from

the regular load combinations.

If the beam-to-column connection is modeled with a pin in the program by

releasing the beam end, it automatically affects the beam connection shear.

4.7.5 24BEvaluation of Brace Connection Forces

For each steel brace in the structure, the program reports the maximum axial

force at each end of the brace for the design of the brace-to-beam connections.

Joint Design 4 - 15

Steel Frame Design CSA S16-09

The brace connection forces reported are the maxima of the factored brace

axial forces obtained from the loading combinations.

For special seismic design, the brace connection forces are not taken less than

the following special values for different types of framing. The special seismic

requirements additionally checked by the program are dependent on the type of

framing used.

Brace axial forces for seismic designs are evaluated for braced frames (SCBF,

OCBF) only. No special checks are performed for moment frames (OMF,

SMF).

 For SCBF, the bracing connection force is taken as the following value (IS

12.8.3.1):

a. The expected yield strength in tension of the bracing member, deter-

mined as 1.1

(IS 12.8.3.1(a)).

 For OCBF, the bracing connection force is taken as the minimum of the two

values (IS 12.7.3):

a. The expected yield strength in tension of the bracing member, deter-

mined as 1.2

(IS 12.7.3.1(a)).

b. The maximum load effect of the amplified seismic load combination (IS

12.2.3, 12.7.3.1(b)).

 For EBF, no special requirements are checked. The user should refer to spe-

cialist literature.

4 - 16 Joint Design

Chapter 5

Design Output

The program has the capacity to create design output in four major ways –

graphical display, file output, tabular display, and member specific detailed de-

sign information.

The graphical display includes input and output design information for members

visible in the active window; the display can be sent directly to a printer or saved

to a file. The file output includes both summary and detail design data that can be

saved in RTF, HTML and plain text formats. The tabular display output in-

cludes both summary and detail design data that can be displayed or saved in

many formats, including Excel, Access, RTF, HTML and plain text. The

member specific detailed design information shows the details of the calcula-

tion.

The following sections describe some of the typical graphical display, file out-

put, tabular display output, and member specific detailed design information.

Some of the design information is very specific to the chosen steel design code.

This manual addresses "Indian IS 800:2007" design code related output infor-

mation only.

5 - 1

Steel Frame Design IS 800:2007

5.1 Graphical Display of Design Information

The graphical display of design output includes input and output design infor-

mation for all steel frame members that are visible in the active window. The

graphical output can be produced in color or in gray-scaled screen display. The

active screen display can be sent directly to the printer or saved to a file in sev-

eral formats.

Input and output design information for the “Indian IS 800:2007” code includes

the following.

Table 5-1 Graphical Display of Design Information

Design Input Information

Design Output Information

 Design sections

 Design framing type

 Live load reduction factors

 Unbraced length ratios, L-factors,

for major and minor direction of bending,

and for lateral-torsional buckling

 Effective length factors for braced condition, K1,

for major and minor directions of bending

 Effective length factors for sway condition, K2

factors, for major and minor directions

of bending

 Effective length factor, KLTB, for

lateral-torsional buckling

 Cm factors for major and minor directions of

bending, and for lateral-torsional buckling (Cmz,

Cmy, CmLT)

 Amplification factors (Kz, Ky, KLT) for major and

minor directions of bending

 C1 factors

 Yield stress, fy

 Design axial capacities (Pd, Td)

 Design bending capacities (Mdz, Mdy, Mcr)

 Design shear capacities (Vdy, Vdz)

 P-M stress ratio values with members

color-coded based on the ratio

 P-M colors and shear stress ratio val-

ues

 P-M ratio colors and no values

 Continuity plate and doubler plate

thickness

 Beam/column capacity ratios

 Beam connection shear

 Brace connection axial force

 Identify the P-M failure

 Identify the shear failure

 Identify all failures

Note that only one of the listed items can be displayed on the model at a time.

Use the Design menu > Steel Frame Design > Display Design Info command

to plot design input and output values directly on the model. The Display Steel

Design Results form shown in Figures 5-1 and 5-2 will display.

5 - 2 Graphical Display of Design Information

Chapter 5 Design Output

Figure 5-1 Choice of design input data for display on the model

in the active window

Figure 5-2 Choice of design output data for display on the model

in the active window

Choose the Design Output or Design Input option. One item can be selected

from the drop-down list. For example, the P-M interaction ratios can be dis-

played by choosing the Design Output option and selecting P-M Ratio Colors &

Values from the drop-down list. Click the OK button to display the PM-Ratio in

the active window. A typical graphical display is shown in Figure 5-3.

Graphical Display of Design Information 5 - 3

Steel Frame Design IS 800:2007

Figure 5-3 A typical graphical display

The graphics can be displayed in 3D or 2D mode. The standard view transfor-

mations are available for all steel design information displays. Several buttons

on the toolbar can be used to switch between 3D and 2D views. Alternatively,

click the View menu and the Set 3D View or Set 2D View commands.

The onscreen graphical display can be sent to printer using any of the following

commands. Use the File menu > Print Graphics command to print the active

window. To capture the graphical display in a file for printing through another

application, use the File menu > Capture Enhanced Metafile command to

create an .emf file, or use the File menu > Capture Picture command to create

a bitmap (.bmp) file. Create a screen capture of the active window using the Alt+

Print Screen keyboard keys or create a screen capture of the entire window

using the Ctrl + Print Screen keyboard keys. Then use the Ctrl+V keyboard

keys to paste the saved image into Paint or other graphical program.

By default the graphical displays are in color. It may be advantageous to view or

present the display in gray-scale graphics or using a white background. Use the

Options menu > Color command to set these options.

5 - 4 Graphical Display of Design Information

Chapter 5 Design Output

5.2 Tabular Display of Design Information

In addition to model definition and analysis results, the design information for

all steel frame members or for only selected members can be displayed in tabular

spreadsheet format. Currently, the program generates design summary data,

PMM design details and shear design details. The tabular spreadsheet output can

be displayed by selecting the Display menu > Show Tables command to access

the Choose Tables for Display form, an example of which is shown in Figure

5-4. That form can be used to choose which tables or sets of tables are to be

displayed.

Figure 5-4 Choice of design data tables for tabular display

The names of the tables are displayed in a tree structure, which can be collapsed

or expanded by clicking on an item in the tree. Click on the small check boxes

preceding the items to select those tables for display. If a branch of the tree is

selected, all of the tables under that branch are selected. The selected set of ta-

bles can be saved as a Named Set using the Save Named Set button. This named

Tabular Display of Design Information 5 - 5

Steel Frame Design IS 800:2007

set can be used in the future for quick selection. If one or more frame members

are selected on the structural model before accessing the Choose Tables for

Display form, the Selection Only check box will be checked when the form

displays and, the program will display information for the selected members

only; uncheck the check box to display information for all applicable members

in the model. If the Show Unformatted check box is checked, the numbers will

be displayed unformatted, instead of being displayed using a limited number of

decimal digits. The unformatted option provides higher precision output that can

then be copied into other programs.

Use the other buttons in the form to tailor the data display. For example, click the

Select Load Patterns button to specify which load patterns are to be included in

the display of model definition data; click the Select Load Case and Modi-

fy/Show Options to specify which load cases are to be included and how

analysis results are displayed.

After selecting all of the tables for steel frame design and the display options,

click the OK button to display a form showing one of the selected design tables,

with a drop-down list in the upper right-hand corner of the form that can be used

to select other tables for display. A typical design table is shown in Figure 5-5.

Use the scroll bars on the bottom and right side of the tables to scroll right and

left or up and down if portions of the data table can not be displayed in the form's

display area. The columns can be resized by clicking the left mouse button on

the separator of the headers, holding down the left mouse button and then

dragging the mouse to the left or right. Reset the column widths to their default

values by selecting the Format-Filter-Sort menu > Reset Default Column

Widths command on the form. The table can be split into two or more tables by

clicking on the small black rectangular area near the bottom-left corner of the

table, holding down the left mouse button, and then dragging the mouse button

to the left or right. Repeat this process to add more splits. Use the split and

horizontal scroll bar to put two columns side by side for easier comparison. The

splits can be removed by selecting the Format-Filter-Sort menu > Remove

Splits command on the form. Alternatively, remove the split by clicking, hold-

ing and dragging the left mouse button to merge the split key to its original lo-

cation.

5 - 6 Tabular Display of Design Information

Chapter 5 Design Output

Figure 5-5 A typical tabular display of design data

Select multiple consecutive columns by putting the cursor on the header, holding

down the mouse button, and then dragging the mouse button left or right. Al-

ternatively, depress the Shift key and click the left mouse button to select a range

of columns.

Each of the individual fields (columns) can be formatted. Fields with text in-

formation can be set for specific types of alignment (center, left, right) and to

specific widths. In addition to setting the alignment and column widths, fields

with numeric data can be set for the maximum number of characters, zero tol-

erance, number of decimal digits and so forth. The tables can be formatted, fil-

tered and sorted using multiple criteria accessed using the Format-Filter-Sort

menu on the form. Filtering and sorting features can be useful in identifying

critical cases. After specifying the table formatting information, save it to a

format file that can be used in the future by selecting the appropriate feature

available under the Format-Filter-Sort menu.

The current table (i.e., the table in the active window) can be exported to Excel,

Access, .rtf., .html, and plain text formats. In both Excel spreadsheet and Access

database formats, the tables can have many columns, making the tables very

Tabular Display of Design Information 5 - 7

Steel Frame Design IS 800:2007

wide. In .rft and .html formats, the tables are split at convenient points to make a

reasonably printable document. In plain text format, the tables can be saved with

or without the splits. To export a table to Excel, for example, select the File

menu > Export Current Table > To Excel command. The program will export

the entire table to an Excel spreadsheet workbook and will automatically open

the file in MS Excel. Similarly, if the table is exported to other formats, the

default editor specific to that format will open the document, provided that the

editor is available in the computer. The table will be saved in that format only if

the relevant editor is not available. Instead of exporting or displaying the cur-

rently displayed table, the entire set of available tables can be exported and

displayed in the afore-mentioned formats by selecting the File menu and the

appropriate submenu command. With these exporting and display features, the

tables can be saved in many required formats and can be printed. Many other

features of the design tables are left for the user to discover by using the pro-

gram.

The preceding description is for SAP2000. ETABS differs slightly.

5.3 Detailed Display of Member Specific Information

The program has the capability to display the design details for a specific

member. The information includes member identification, shape name, section

properties, design combination name, design combination forces, and other de-

sign input data to check the design results. The information also includes stress

ratios for P-M-M and other interactions, demand/capacity ratios from shear,

nominal strengths, design factors such as K1 (braced), K2 (sway), Cmz, Cmy, CmLT,

Kz, Ky, KLT, and so forth. The design details are displayed in a summary form and

also are displayed for a specific load combination and for a specific station of a

frame member.

When the design results are displayed on the model in the active window, the

detailed design information can be accessed by right clicking on the desired

frame member to display the Steel Stress Check Information form. Alterna-

tively, click the Design menu > Steel Frame Design > Interactive Steel

Frame Design command and then right click on the frame member. An example

of that form is shown in Figure 5-6.

5 - 8 Detailed Display of Member Specific Information

Chapter 5 Design Output

Figure 5-6. A typical member specific steel stress check information summary

The Steel Stress Check Information form identifies the frame members and the

analysis and design section, and includes a display area of mostly de-

mand/capacity ratio data and a set of buttons that access forms that provide

further details about the selected frame member. The display area reports the

load combinations, the stress check stations, the P-M-M interaction ratio along

with its axial and flexural components, and the shear stress ratios. The load

combination is reported by its name, while the station is reported by its location,

which is measured from the I-end of the column. The number of reported line

items in the text box is equal to the number of design combinations multiplied by

the number of stations. Only one line item is highlighted in blue when the form

first displays. That item highlights the largest demand/capacity ratio from

P-M-M, major and minor shear or any other considered interaction ratio, unless

a line item(s) has design overstress or an error. In that case, the item with the

overstress or error will be selected and highlighted. If many line items are

overstressed or have an error, the last among all such line items will be selected

and highlighted.

Detailed Display of Member Specific Information 5 - 9

Steel Frame Design IS 800:2007

The stress check information is always reported for the design section. If the

member is assigned an individual section, the analysis and design section are

always the same. If the member is assigned an Auto Select Section (a list of

sections), the analysis and design section can be different, unless the design has

converged.

The Overwrites and Details buttons near the bottom of the Steel Stress Check

Information form can be used to access the Steel Frame Design Overwrites form,

and the Steel Stress Check Data form, which displays detailed information about

the selected frame element. While the latter form displays information in a

non-editable format, the Overwrites form display the overwrite data in editable

format. This allows the user to enter an interactive mode of design.

 Overwrites button. Click this button to access the Steel Frame Design

Overwrites form. Use that form to make revisions to the steel frame design

overwrites and then immediately review the new design results as a summary

using the Steel Stress Check Information form, or in detail by clicking the

Details button to access the Steel Stress Check Data form. Clicking the OK

button on the Steel Frame Design Overwrites form temporarily saves any

changes. To make the changes permanent, click the OK button on the Steel

Stress Check Information form. To disregard the changes, click the Cancel

button on the Steel Stress Check Information form. An example of an Over-

writes form is shown in Figure 5-7.

 Details button. Click this button to access the Steel Stress Check Data form.

Use the form to review all of the design details for the highlighted item. An

example of a Steel Stress Check Data form is shown in Figure 5-8. The in-

formation includes the member ID, load combo and station identifications,

steel design sections, section properties, design combination forces, stress ra-

tios for P-M-M and other interactions, stress ratios for shear, nominal

strengths, and design factors such as, K1 (braced), K2 (sway), Cmz, Cmy, CmLT,

Kz, Ky, KLT, and so forth. Values that are not applicable are reported as N/A.

Similarly, N/C and N/N indicate an item is “Not Calculated” and “Not

Needed.”

5 - 10 Detailed Display of Member Specific Information

Chapter 5 Design Output

Figure 5-7. A typical member specific Steel Frame Design Overwrites form

Figure 5-8 A typical Steel Stress Check Data form

Detailed Display of Member Specific Information 5 - 11

Steel Frame Design IS 800:2007

Before clicking the button, highlight an item for the desired design station and

design load combination in the Steel Stress Check Information display area by

clicking on the line. The data subsequently displayed will relate to the high-

lighted item. By default, the most critical line item is selected when the form first

displays, as described previously.

To increase or decrease the width of the Steel Stress Check Data form, put the

cursor near the right edge of the form, click the left mouse button, and drag the

mouse cursor towards the left or right. Similarly, the height of the form can be

increased or decreased.

The text in the form can be dragged in any direction by positioning the cursor in

the middle of the form, and then clicking the left mouse button and dragging the

text in the desired direction.

Use the Units drop-down list in the upper right-hand corner of the form to

change the units used to display the data. Data displayed on the form can be sent

directly to the printer by selecting the File menu > Print command on the form.

The program allows limited page setup options using the Print Setup Com-

mand on the File menu on the form.

The Steel Stress Check Information form also includes a Tabular Data button

that when clicked displays member specific design details in a spreadsheet type

format. The tabular display of design information has been described in the

previous section. In that case, the information displayed is specific to the se-

lected member only. The tabular output is shown for all stations and all design

load combinations for the selected member. An example of design details table

that displays after clicking the Tabular Data button is shown in Figure 5-9. This

button is available in SAP2000, but not in ETABS.

5 - 12 Detailed Display of Member Specific Information

Chapter 5 Design Output

Figure 5-9 Member specific design details in tabular format

5.4 Save or Print Design Information as Tables

In addition to model definition and analysis results, the design information for

all steel frame members or for selected frames only can be saved in tabular

format. Currently for “Indian IS 800:2007” code, the program saves design

summary data, PMM design details, and shear design details.

Save the file output by selecting the File menu > Print Tables command to

access the Choose Tables for Printing form. An example of that form is shown in

Figure 5-10. Use the options on the form to choose which table or set of tables to

save in a file or print. This form is very similar to the Choose Tables for Display

form, which has been described earlier in this chapter in the "Tabular Display of

Design Information" section.

Save or Print Design Information as Tables 5 - 13

Steel Frame Design IS 800:2007

Figure 5-10 Choice of design tables for saving in a file or printing

The name of the tables are displayed in a tree structure, which can be collapsed

or expanded by clicking on an item in the tree. Click on the small check boxes

preceding the items to select those tables for printing or saving to a file. If a

branch of the tree is selected, all of the tables under that branch are selected.

When all options for printing or saving the data to file have been specified, the

settings can be saved as a Named Set using the Save Named Set button. The

Named Set can be easily recalled in the future, reducing the need to reselect the

options and ensuring that output is consistent from one printing effort to another.

If one or more structural members are selected before the Choose Tables for

Printing form is accessed, the Selection Only check box will be checked, and the

program will save or print the data for the selected members only; uncheck the

check box to save or print the data for all appropriate members.

5 - 14 Save or Print Design Information as Tables

Chapter 5 Design Output

The output can be generated in a variety of formats, including rich text format

(.rft), plain text with and without splits or page breaks (.txt), and hyperlink text

markup language (.htm) by choosing the appropriate option on the right side of

the form.

Printed output can be specified to have a landscaped orientation, in which the

width of the resulting printout on a given page is longer than the height of the

printout.

Filtering criteria can be applied if those criteria were specified using the For-

mat-Filter-Sort menu > Format Table command when the selected data tables

were displayed using the Display menu > Show Tables command. The output

also can be specified to include a hyperlinked contents to facilitate accessing

specific areas of the printout.

There are other buttons on the form that do not affect saving or printing design

information. For example, the Select Load Patterns button affects only sav-

ing/printing model definition data. The Select Load Cases and Modify/Show

Options buttons affect only saving/printing analysis results.

After clicking all the necessary tables for steel frame design and all necessary

options, clicking the OK button will save/print the design tables.

Although the File name > Print Tables command path is dedicated for sav-

ing/printing design information, it is not the only path to do so. Design tables can

be saved in different formats using the path Display menu > Show Tables

command.

The preceding description applies to SAP2000. ETABS differs slightly.

5.5 Error and Warning Messages

Error messages and warnings may be displayed in the steel frame design output.

Those messages and warnings are assumed to be self explanatory.

Error and Warning Messages 5 - 15

Bibliography

IS, 2007. IS 800:2007 – Indian Standard – General Construction in Steel – Code

of Practice, Third Revision. December. Bureau of Indian Standards, Manak

Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi 11002, India.

IS, 2002. IS 1893 (Part 1): 2002 – Indian Standard – Criteria for Earthquake

Resistant Design of Structures, Part 1 General Provisions and Buildings,

Fifth Revision. June. Bureau of Indian Standards, Manak Bhavan, 9 Baha-

dur Shah Zafar Marg, New Delhi 11002, India.

IS, 1997. IS 875 (Part 3):1997 – Indian Standard – Code of Practice for Design

Loads (Other than Earthquake) for Buildings and Structures Part-3 Wind

Loads, Second Revision. Bureau of Indian Standards, Manak Bhavan, 9

Bahadur Shah Zafar Marg, New Delhi 11002, India.

AISC, 2005. ANSI/AISC 360-05: An American National Standard – Specifi-

cation for Structural Steel Building, American Institute of Steel Construc-

tion, One East Wacker Drive, Suite 700, Chicago, Illinois, 60601. March 9.

CSI, 2008. CSI Analysis Reference Manual, Computers and Structures, Inc.,

Berkeley, California.

CSI, 2007. CSI Lateral Load Manual. Computers and Structures, Inc., 1995

University Avenue, Berkeley, California, 94704.

Bibliography - i

Concrete Frame Design IS 456 2000

White, D. W. and J. F. Hajjar, 1991. “Application of Second-Order Elastic

Analysis in LRFD: Research to Practice,” Engineering Journal, American

Institute of Steel Construction, Inc., Vol. 28, No. 4.

ii - Bibliography

SFD IS 800 2007

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