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

Copyright
Copyright  Computers & Structures, Inc., 1978-2015
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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

Introduction
1.1

Organization

1-2

1.2

Recommended Reading/Practice

1-3

Chapter 2
Modeling, Analysis and Design Prerequisites

This chapter provides an overview of the basic assumptions, design preconditions, 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.

2.1

•

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."

Check and Design Capability
The program has the ability to check adequacy of a section (shape) in accordance 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 combination. It calculates the envelope of the D/C ratios. It also checks the other requirements 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 optimized. The program will use the median section by weight when doing the initial analysis. Refer to the program Help for more information about Auto Select 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 design 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 current design section is the W16X31. Before the design process is complete, verify 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 separately. Note the following about analysis and design sections:

2-2

Analysis Sections vs. Design Sections

Chapter 2 Design Algorithms

2.3



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

Design and Check Stations
For each design combination, steel frame members (beams, columns, and braces) are designed (optimized) or checked at a number of locations (stations)
along the length of the object. The stations are located at equally spaced segments 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 indicates 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 defined station for each design combination. The bending moments are calcuDesign and Check Stations

2-3

Steel Frame Design IS 800:2007

lated about the principal axes. For I-Shape, Box, Channel, T-Shape, Double-Angle, Pipe, Circular, and Rectangular sections, the principal axes coincide with the geometric axes. For Single-Angle sections, the design considers 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 computations 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.



2.5

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 exceeded a limit state.

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 default design load combinations. An unlimited number of design load combinations 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 added 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 combinations should be defined in lieu of or in addition to the default design load combinations.
For multi-valued design combinations, such as those involving response spectrum, 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 combinations with negative factors for response spectrum load cases are not
required because the program automatically takes the minima to be the negative 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

δ
Final deflected position of the
frame element that includes the
global lateral translation, ∆, and
the local deformation of the
element, δ

Position of frame element
as a result of global lateral
translation, ∆, shown by
dashed line

P
Figure 2-1 P-∆ and P-δ 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:
=
M CAP δ b ( M nt + δ s M lt )

where,
M CAP = Required flexural design capacities
M nt

= Required flexural capacities from first-order analysis of the
member assuming there is no translation of the frame (i.e., associated with the δ deformation in Figure 2-1)

M lt

= 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)

δs

= Unitless amplification factor multiplying M lt

δb

= Unitless amplification factor multiplying ( M nt + δ s M 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 δs (i.e., δs is equal to 1). However, 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 δb 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 breaking 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 lateral 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 modify the default design load combinations to include the notional loads with appropriate 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 slenderness effects for flexural buckling and for lateral-torsional buckling. The program automatically determines the unsupported length ratios, which are specified 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 design overwrite option.
Two unsupported lengths, L33 and L22, as shown in Figure 2-2 are to be considered for flexural buckling. These are the lengths between support points of the
member in the corresponding directions. The length L33 corresponds to instability 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 l33 and l22

Member Unsupported Lengths

2-9

Steel Frame Design IS 800:2007

In determining the values for L22 and L33 of the members, the program recognizes various aspects of the structure that have an effect on these lengths, such
as member connectivity, diaphragm constraints, and support points. The program automatically locates the member support points and evaluates the corresponding 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 direction 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 buckling 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 lateraltorsional 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 affects only the unbraced lengths for minor direction bending (L22) and lateraltorsional 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 considerations. “Automatic” calculation of the unbraced length is based on member 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. Also 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” calculation 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 allows 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-bymember basis. If the frame is not really a sway frame, the user should overwrite 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 minor 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-bymember 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 basically that of a moment-resisting frame for which the K-factor calculation is relatively complex. For the purpose of calculating K-factors, the objects are identified 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 stiffness summations for each joint in the structural model:
cE I
Scx = ∑  c c 
 Lc  x

cE I
Sbx = ∑  b b 
 Lb  x

cE I
Scy = ∑  c c 
 Lc  y

cE I
Sb y = ∑  b b 
 Lb  y

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
EI 22 L22 and EI 33 L33 are rotated to give components along the global X and

Y directions to form the ( EI L ) x and ( EI L ) y values. The correlation factor

for effective flexural stiffness, c, is taken as 1, disregarding the code recommendation (IS Table 35). Then for each column, the joint summations at ENDI 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

SI
β I 22 =I c 22 I
S b 22 + Sc 22

SJ
β J 22 =J c 22 J
S b 22 + Sc 22

SI
β I 33 =I c 33 I
S b 33 + Sc 33

SJ
β J 33 =J c 33 J
S b 33 + Sc 33

Finally, if β I and β J are known for a particular direction, the column Kfactors for the corresponding direction is calculated from the following relationship for α:
1 − 0.2 ( β1 + β2 ) − 0.12β1β2 
K =

 1 − 0.8 ( β1 + β2 ) + 0.6β1β2 

0.5

This relationship is the mathematical formulation for the evaluation of Kfactors 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 important 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 direction, 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 + 0.145 ( β1 + β2 ) − 0.265β1β2 
K= 
 2 − 0.364 ( β1 + β2 ) − 0.247β1β2 

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 single element. However, the user can request that the program break a member
internally at framing intersections and at specified intervals. In this way, accuracy in modeling can be maintained at the same time that design/check specifications 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 unbraced 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 bottom of the flange of the beam framing the column at the top. The automatically calculated length factor typically becomes less than 1. If there are intermediate 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 unbraced length correctly, provided that there is no intermediate bracing
point.
2. K-factor: Even if the user breaks the member into pieces, the program typically 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 segments do not represent the brace-to-brace unsupported length, the program
calculated Cm factor is conservative. If this conservative value is acceptable, 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-δ 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 principal 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 requirements 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 beamcolumn 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 column flanges, in which case the shear stresses are seldom critical, and the program 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, 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. When code appropriate, 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 procedure 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 procedure 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 member frame design procedure to steel frame design, composite beam design, default, or no design. Change the design procedure by selecting the member(s)
and clicking the Design menu > Overwrite Frame Design Procedure command. 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 assumptions 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 automatically perform the iterative steel frame design process. To initiate the process, first use the Design menu > Steel Frame Design > View/Revise Preference command and set the maximum number of auto iterations to the maximum 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) comparing 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 presented in the subsequent chapters correspond to that specific system of units unless
otherwise noted. For example, the IS 800:2007 code is published in millimeterNewton-second units. By default, all equations and descriptions presented in
this manual correspond to millimeter-Newton-second units. However, any system 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."

•

3-1

Reference to the ANSI/AISC 360-05 code (specialist literature) is identified with the prefix “AISC.”

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.
A

Cross-sectional area, mm2

Effective section area, mm2

Gross cross-sectional area, mm2

Net effective area of cross-section, mm2

Shear area, mm2

Av2, Av3

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

CmLT

Equivalent uniform moment factor for lateral-torsional buckling

Cmy

Equivalent uniform moment factor for minor bending

Cmz

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 =

π2 E

( KL r )

fcd

Design compressive stress, N/mm2

Steel ultimate strength, N/mm2

Steel yield strength, N/mm2

fyw

Steel yield strength of the web, N/mm2

Shear modulus, N/mm2

Overall depth of the section, mm

Web height, mm

Moment of inertia, mm4

I22, Iy

Minor moment of inertia, mm4

I33,Iz

Major moment of inertia, mm4

St. Venant torsional constant for the section, mm4

Effective length factor

K33, K22

Effective length K-factors in the major and minor directions

KLT

Moment magnification factor for lateral-torsional buckling

KLTB

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

L22, L33

Laterally unbraced length of member for major and minor axes bending, mm

LLT

Effective buckling length, mm

LLTB

Unbraced length for lateral-torsional buckling, mm

Design factored bending moment, N-mm

Design bending resistance, N-mm

Mdv

Reduced design bending resistance accounting for shear,
N-mm

My, M22

Design bending moment about minor axis bending, N-mm

Mz, M33

Design bending moment about major axis bending, N-mm

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

Ncr

Elastic critical force, N

Design strength in tension, Td, or compression strength due to
yielding given by
=
N d Ag f y γ m 0

Design axial compression force, N

Design compressive strength, N

Radius of gyration, mm

r33, r22

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

Tdg

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

Tdn

Design ultimate tensil strength due to rupture, N

Flange thickness, mm

Web thickness, mm

Design factored shear force, N

Vcr

Design shear buckling resistance, N

Design shear strength, N

Elastic section modulus, mm3

Ze33,Ze22

Major and minor elastic section moduli, mm3

Plastic modulus, mm3

Zp33,Zp22

Major and minor plastic section moduli, mm3

Value for calculating the reduction factor χ

φLT

Value for calculating the reduction factor χLT

Imperfection factor for axial compression

αLT

Imperfection factor for lateral-torsional buckling

α1, α2

Coefficients used in an interaction equation (IS 9.3.1.1)

3.2

Reduction factor of moment capacity to account for shear
forces

βb

Moment capacity adjustment factor for appropriate class of
section

Stress reduction factor for buckling

χLT

Stress reduction factor for lateral-torsional buckling

Coefficient dependent on fy, 250 f y

γM0

Partial factor for the resistance of cross-sections and buckling

γM1

Partial factor for the resistance governed by ultimate stress

Non-dimensional slenderness,

λp,λr,λs

Slenderness parameters for classification

λLT

Non-dimensional slenderness for lateral-torsional buckling

λw

Non-dimensional web slenderness ratio

Ratio of moments in a segment

KL
rπ

fy
E

for flexural buckling

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
Design Code

Possible Values
Design codes
available in the
current version

Default Value

Description

AISC360-05/
IBC 2006

The selected design code. Subsequent design is based
on this selected code.

Table 3-1: Steel Frame Design Preferences
Item
Multi-Response Case
Design

Framing Type

Importance Factor

Seismic Zone

Consider P-Delta
Done?

Possible Values

Default Value

Description

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. Stepby-Step considers step-by-step values for Time History 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. Stepby-Step - All considers step-by-step values for Time
History, Multi-step static and Nonlinear static. Stepby-Step and Step-by-Step - All default to the corresponding Envelope if more then one multivalued
case is present in the combo.

SMF, OMF, SCBF,
OCBF, EBF,
Secondary

SMF

This item is used for ductility considerations in the
design.

1.0

This is related to seismic design. This depends on the
functional use of the structure, hazardous consequences of its failure, post-earthquake functional
needs, and so on (IS 1893 6.4.2).

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).

Yes/No

It affects K-factor calculation. If P-∆ analysis is
completed, K is taken as if the structure is braced.

GammaM0

1.1

Partial factor for the resistance of cross-sections and
buckling.

GammaM1

1.25

Ignore Seismic Code?

Yes, No

Toggle to consider (No) or not consider (Yes) the
seismic part of the code in design.

Ignore Special
Seismic Load?

Yes, 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).

Partial factor for the resistance of members to
ultimate stress.

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 is 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. Inputting 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 acceptability. 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 Overwrite items. Thus, it is not necessary to specify or change any of the Overwrites. However, at least review the default values to ensure they are acceptable. When changes are made to Overwrite items, the program applies the
changes only to the elements to which they are specifically assigned. Overwritten 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

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.

SMF, OMF, SCBF,
OCBF, EBF, Secondary

From
Preferences

This item is used for ductility considerations in the
design.

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 buckling about the major axis. This determines the axial
compression capacity for buckling about the major
axis. It determines the imperfection factors for buckling 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 buckling about the minor axis. This determines the axial
compression capacity for buckling about the minor
axis. It determines the imperfection factors for buckling 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 determination.

Consider Deflection?

Yes/No

Toggle to consider (Yes) or not consider (No) deflection.

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.

Current Design
Section

Fame Type
Section Class

Deflection Check
Type

Description

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

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 subtracted from the total load deflection to get net
deflection. Inputting a value of 240 means that the
limit is L/240. Inputting zero means 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 determined.

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. Specifying 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. Specifying 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 object. 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 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 always taken as 1,
regardless of any other value specified in the Overwrites. 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 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 always taken as 1,
regardless of any other value specified in the Overwrites. 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 program determined. For beam design, this factor is
always 1, regardless of any other values specified in
the Overwrites. The factor is used for axial compression 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 program determined. For beam design, this factor is
always 1, regardless of any other values specified in
the Overwrites. The factor is used for axial compression 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 diagram. 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 determining 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 lateraltorsional 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 determined. 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 bending. Specifying zero means the value is program
determined.

Minor Bending
Capacity, Mdy

≥0

Calculated

Design bending moment capacity in minor axis bending. 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
Demand/Capacity
Ratio Limit

3.4

Possible Values

Default Value

Description

≥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.

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 analysis cases, such as dead load (DL), live load (LL), wind load (WL), and horizontal earthquake load (EL).
For the IS 800:2007 code, the following default design combinations are generated by the program (IS 3.5.1, 5.3.3, Table 4):
1.5DL
1.5DL + 1.5L

(IS 3.5.1, 5.3.3, Table 4, Line 1)
(IS 3.5.1, 5.3.3, Table 4, Line 2)

1.5DL ± 1.5WL
0.9DL ± 1.5WL
1.2D + 1.2WL + 1.2W
1.2D + 1.2L ± 0.6W

(IS 3.5.1, 5.3.3, Table 4, Line 4)
(IS 3.5.1, 5.3.3, Table 4, Line 4)
(IS 3.5.1, 5.3.3, Table 4, Line 3)
(IS 3.5.1, 5.3.3, Table 4, Line 2)

1.5D ± 1.5E
0.9D ± 1.5E
1.2D + 1.2L ± 1.2E

(IS 3.5.1, 5.3.3, Table 4, Line 4)
(IS 3.5.1, 5.3.3, Table 4, Line 4)
(IS 3.5.1, 5.3.3, Table 4, Line 3)

The code is required to consider Notional Load in the design loading combinations 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-ofrecord. 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 flexure, the sections are classified as Plastic (Class 1), Compact (Class 2), SemiCompact (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 applicable.
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 section is Semi-Compact (Class 3). If the width-thickness ratio of any element exceed 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, Table 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 direction 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.
(c) For plates, the width b is the distance from the free edge to the first row of
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 element dimensions.
For stiffened (internal) elements supported along two edges parallel to the direction 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.

(c) For flanges of rectangular hollow structural sections (HSS), the width b is
the clear distance between webs. For webs of rectangular HSS, d is the
clear distance between the flanges.
Table 3-3

Doubly Symmetric I-Shape

Section
Type

Limiting Width-Thickness Ratios of Compression Elements for
Classification Sections

Description
of Element

Example

WidthThickness
Ratio,
(λ)

Limiting Width-Thickness Ratios for Compression
Element
Plastic
Compact
Semi-Compact
Class 1
Class 2
Class 3
λp
( λr )
(λs )

( )

Flexural
compression
of flanges of
rolled
I-Shapes

b tf

9.4ε

10.5ε

15.7ε

Flexural
compression
in flanges of
built-up
I-Shapes

b tf

8.4ε

9.4ε

13.6ε

Axial only
compression
in flanges of
rolled
I-Shapes

b tf

9.4ε

10.5ε

15.7ε

Axial only
compression
in flanges of
built-up
I-Shapes

b tf

8.4ε

9.4ε

13.6ε

126ε
≥ 42ε
1 + 2r2

42ε

Flexure in web

d tw

84ε
≥ 42ε
1 + r1

if r ≤ 0
105ε
1 + r1
if r > 0
105ε
≥ 42ε
1 + 1.5r1

Web in axial
only
compression

d tw

Table 3-3

Double Channel

Channel

Section
Type

Limiting Width-Thickness Ratios of Compression Elements for
Classification Sections

Description
of Element

Example

WidthThickness
Ratio,
(λ)

Limiting Width-Thickness Ratios for Compression
Element
Plastic
Compact
Semi-Compact
Class 1
Class 2
Class 3
λp
( λr )
(λs )

( )

Flexural
compression
in flanges

b tf

9.4ε

10.5ε

15.7ε

Axial only
compression
in flanges

b tf

9.4ε

10.5ε

15.7ε

Flexure in web

d tw

42ε

Web in axial
only
compression

d tw

42ε

Flexural
compression
in flanges

b tf

9.4ε

10.5ε

15.7ε

Axial only
compression
in flanges

b tf

9.4ε

10.5ε

15.7ε

Flexure in web

d tw

42ε

Web in axial
only
compression

d tw

42ε

Table 3-3

Section
Type

Limiting Width-Thickness Ratios of Compression Elements for
Classification Sections

Description
of Element

WidthThickness
Ratio,
(λ)

Example

Flexural or
axial
compression
of flanges
under major
axis bending

( )

29.3ε

33.5ε

42ε

126ε
> 42ε
1 + 2r2

Double Angle

T-Shape

Box

b tf

Limiting Width-Thickness Ratios for Compression
Element
Plastic
Compact
Semi-Compact
Class 1
Class 2
Class 3
λp
( λr )
(λs )

Flexure in web

d tw

84ε
> 42ε
1 + r1

if r ≤ 0
105ε
1 + r1
if r > 0
105ε
> 42ε
1 + 1.5r1

Flexural or
axial
compression
in flanges

b tf

9.4ε

10.5ε

15.7ε

Compression
in stems

d tw

8.4ε

9.4ε

18.9ε

Any type of
compression
in leg

b t

9.4ε

10.5ε

15.7ε

b t

9.4ε

10.5ε

15.7ε

(b + d ) t

―――

25ε

b t

9.4ε

10.5ε

15.7ε

b t

9.4ε

10.5ε

15.7ε

(b + d ) t

―――

25ε

Any type of
compression
in leg

t
b

t
d

Angle

Flexural
compression
in any leg

Axial only
compression
in any leg

Table 3-3

Description
of Element

Example

WidthThickness
Ratio,
(λ)

Limiting Width-Thickness Ratios for Compression
Element
Plastic
Compact
Semi-Compact
Class 1
Class 2
Class 3
λp
( λr )
(λs )

( )

Flexural
compression

D t

42ε2

52ε2

146ε2

Axial only
compression

D t

―――

88ε2

Pipe

Section
Type

Limiting Width-Thickness Ratios of Compression Elements for
Classification Sections

Round
Bar
Rectangular
General
SD
Section

―――

Assumed Compact

―――

Assumed Compact

―――

Assumed Compact

―――

Assumed Compact

Refer to Table 3-3 (IS Table 2) for the graphic representation of stiffened element dimensions.
The various parameters used in calculating the width-to-thickness ratio limits
are defined as:
ε = 250 f y
r1 = −

r2 = −

P
( dtw ) f y γ 0
P
Af y γ 0

(IS Table 2 Notes)
(IS Table 2 Notes)

(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.

b ft

k
hp 2
tw

PNA
NA

hc 2
d

tf
b

b fc

b
=
b b f − 3tw

k
tw
d

hc= d − 3t f

tf
tf
bf

bf
bf
b

bf
s

tf
d

d
b

tw
IS 800:2007 : Axes Conventions
2-2 is the cross section axis
parallel to the webs, the
longer dimension of tubes,
3, z
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.

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

2, y

3, z

2, y

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 relationships 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, PDelta 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, Circular, 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 members 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:
T
≤ 1.0
Td

(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 design 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:
=
Tg Ag f y γ m 0

(IS 6.2)

= 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
=
Tdn 0.9 An fu γ m1

(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 fastener 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 area, A, minus fastener holes and other openings. The net effective area, An, is assumed to be equal to the gross cross-sectional area, Ag, by default. For members that are connected with welds or members with holes, the An A g ratio
must be modified using the steel frame design Overwrites to account for the effective 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 crosssections, 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:
fy γ m0
fcd =
=
χf y γ m 0 ≤ f y γ m 0
0.5
φ + φ2 − λ 2 

(IS 7.1.2.1)

where
φ

= 0.5 [1 + α ( λ − 0.2 ) + λ 2 ]

= non-dimensional effective slenderness ratio
f y fcc
=
=

KL
rπ

(

f y KL

)

(IS 7.1.2.1)

π2 E

(IS 7.1.2.1)

fcc = Euler buckling stress =

(

π2 E
KL

)

(IS 7.1.2.1)

where
KL r =

effective slenderness ratio or ratio of effective length,
KL, to appropriate radius of gyration, r,

imperfection factor given in IS Table 7

γm0

stress reduction factor
1

(IS 7.1.2)

φ + ( φ2 − λ 2 )0.5 



partial safety factor for material strength.

The effective slenderness ratio, KL r , is given by:
K L K L 
KL
= max  33 33 , 22 22 
r
r22 
 r33

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 major 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
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)
Axis

Buckling
Class

tf ≤ 40 mm

Major
Minor

a
b

40 < tf ≤ 100
mm

Major
Minor

b
c

tf ≤ 100 mm

Major
Minor

b
c

tf > 100 mm

Major
Minor

d
d

tf ≤ 40 mm

Major
Minor

b
c

tf > 40 mm

Major
Minor

c
d

hot rolled

any

b/tf > 30 or h/tw > 30

any

Section Shape

Limits

h/b > 1.2
Rolled I-Sections
h/b ≤ 1.2

Welded I-Sections

Hollow Tube and Pipe Sections
Welded Box

3.8.2.2

b/tf < 30 and h/tw < 30

any

Channel, Tee, Double Channel,
General, Solid Sections, Section
Designer

none

any

Angle and Double Angle Sections

none

any

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, Double Channel, Double Angle, and Angle sections is given by:
Pd = Ae fcd

(IS 7.1.2)

where,
Ae = effective sectional area
fcd =
χf y γ m 0 ≤ f y γ m 0

(IS 7.1.2.1)

1
φ + ( φ2 − λ 2 )0.5 



= 0.5 [1 + α ( λ − 0.2 ) + λ 2 ]

(IS 7.1.2.1)

f y Fe

α = imperfection factor for minor axis bending
Fe is calculated from the following equations:
I-Shapes and Double Channel Sections
 π2 EC
 1 
w

Fe 
GJ
=
+

2
 ( K z Lz )
  I 22 +I 33 



(AISC E4-4)

Channel Sections
 F + Fez
=
Fe  e33
 2H

4 Fe33 Fez H
 
 1 − 1 −
2

( Fe33 + Fez )






(AISC E4-5)






(AISC E4-2)






(AISC E4-5)

Double Angle and T-Shapes
 F + Fez
=
Fe  e 22
 2H

4 Fe 22 Fez H
 
 1 − 1 −
2

( Fe22 + Fez )

Single Angle Sections with Equal Legs
 F + Fez
=
Fe  e33
 2H

4 Fe33 Fez H
 
 1 − 1 −
2

( Fe33 + Fez )

Single Angle Sections with Unequal Legs
Fe is the lowest root of the cubic equation.
2

x 
y 
0
( Fe − Fe33 )( Fe − Fe22 ) ( Fe − Fez ) − F ( Fe − Fe22 )  o  − Fe2 ( Fe − Fe33 )  o  =
 r0 
 r0 
2
e

(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)

xo2 + yo2 +

I 22 + I 33
polar radius of gyration about the shear center
=
Ag

(AISC E4-7)
H

 x 2 + y2 
= 1−  o 2 o 
 r


Fe33 =

Fe 22 =

(AISC E4-8)

π2 E

( K33 L33

r33 )

π2 E

( K 22 L22

(AISC E4-9)

r22 )

 π2 EC
 1
w

GJ
+
Fez = 
2
2
 ( K z LLT )
 Ar0



(AISC E4-10)

(AISC E 4-11)

K22, K33

are effective length factors K2 in minor and major directions.

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 overwritten.

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:
Md =
βb Z p f y γ m 0 ≤ 1.2 Z e f y γ m 0

where
βb

= 1.0 for plastic and compact sections,
= Z e Z p for semi-compact sections,

= plastic section modulus of the cross-section,

= elastic section modulus of the cross-section,

(IS 8.2.1.2)

= 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
M dv=

(1 − β ) M d + βM fd ≤ 1.2 Z e f y

γ m0

(IS 9.2.2(a))

where
β

if V Vd ≤ 0.6
0
=

2
( 2V Vd − 1) , if V Vd > 0.6

(IS 9.2.2(a))

Md = plastic design moment of the whole section disregarding 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 excluding 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
M dv=

(1 − β ) M d + βM fd ≤ Z e f y

γ m0

(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
= Z e Z p for Semi-Compact (Class 3) sections,

Z p , Z e = plastic section modulus and elastic section modulus with respect to extreme compression fiber

fbd

= design bending compressive stress, obtained as given in the
following
fbd = χ LT f y γ m 0

χLT

= bending stress reduction factor to account for lateral-torsional
buckling, given by:

=
χ LT

{

φ LT + φ2LT − λ 2LT 

0.5

}

≤1

=
φLT 0.5 1 + α LT ( λ LT − 0.2 ) + λ LT 2 

αLT

= the imperfection parameter. It is given by:
= 0.21 for rolled steel section, and

(IS 8.2.2)

= 0.49 for welded steel section.
The non-dimensional slenderness ratio, λ LT, is given by:
λ LT = βb Z p f y M cr ≤ 1.2 Z e f y M cr

(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:
π2 EI y  I w L2LT GI t
M cr C1
=
+

LLT  I y π2 EI y





0.5

(IS Annex E, 8.2.2.1)

where Iy, Iw, and It are the minor axis inertia, warping constant, and torsion constant, respectively; LLT is the effective unbraced length for the lateral-torsional
buckling mode, and C1 is defined as:
=
C1 1.88 − 1.40ψ + 0.52ψ 2 ≤ 2.7

(EC3-1993 F1.1(6))

where ψ 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 resistance 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 intermediate stiffness used to enhance shear strength of a section (IS 8.4.2.2).
The design shear strength, Vd, is taken as
V=
Vn γ m 0
d

(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
Vp =

Av f yw
3

(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 — 2 A π
 Plates and Solid Bars — A
where,
A

cross-section area,

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

clear depth of the web between flanges,

overall depth of the section,

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 d tw > 67ε , where ε = 250 f y
(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 =
=
τb =

shear force corresponding to web buckling,
Avτb,
shear stress corresponding to web buckling, determined as follows:
 when λw ≤ 0.8
τb =f yw

(IS 8.4.2.2)

 when 0.8 < λw < 1.2

(

τb = 1 − 0.8 ( λ w − 0.8 )  f yw

)

3 ,

(IS 8.4.2.2)

 when λw ≥ 1.2
=
τb f yw

(

3λ 2w ) ,

(IS 8.4.2.2)

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

f yw

(

)

3τcr ,e ,

(IS 8.4.2.2)

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

K v π2 E

12 (1 − µ 2 ) [ d tw ]

(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 ( c d ) for c d < 1.0
2

= 5.35 + 4.0 ( c d ) for c d ≥ 1.0
2

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 combinations. 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 considered.

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 sections, 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:
α

1
 My 
 Mz 

 +

M
 M ndz 
 ndy 

α2

≤1

(IS 9.3.1.1(a))

In the equation 9.3.1.1(a), there are two basic ratios — major axis bending (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 ratio can be smaller than the individual component ratios when the component 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:
My

≤1

(IS 9.3.1.1(ay))

Mz
≤1
M ndz

(IS 9.3.1.1(az))

M ndy

N
≤1
Nd

(IS 9.3.1.1(an))

where,
M y, M z

= 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),

= design strength in tension, Td, as obtained from IS 6 or
in compression due to yielding given by=
N d Ag f y γ m 0 ,

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

α2 = 2
–

(IS 9.3.1.1, Table 17)
(IS 9.3.1.1, Table 17)

For Rectangular Hollow sections

=
α1

1.66
≤6
1 − 1.13n 2

(IS 9.3.1.1, Table 17)

α2
=

1.66
≤6
1 − 1.13n 2

(IS 9.3.1.1, Table 17)

–

For Circular Tube sections

α1 = 2

(IS 9.3.1.1, Table 17)

α2 = 2

(IS 9.3.1.1, Table 17)

For Solid Rectangular sections

=
α1 1.73 + 1.8n3

(IS 9.3.1.1, Table 17)

=
α 2 1.73 + 1.8n3

(IS 9.3.1.1, Table 17)

In all of the preceding cases, n is taken as
n=

N
Nd

(IS 9.3.1.1, Table 17)

Mndy and Mndz are computed as follows:
–

–

For Solid Rectangular sections
Mndz = M dz (1 − n2 )

(IS 9.3.1.2(a))

Mndy = M dy (1 − n2 )

(IS 9.3.1.2(a))

For Welded I-sections
 1− n 
M ndz = M dz 

 1 − 0.5a 

M ndy

 M dy ,

=
  n − a 2 
 M dy 1 − 
 ,
  1− a  


(IS 9.3.1.2 (b))
for n ≤ a,
for n > a

(IS 9.3.1.2 (b))

where,
=
a

–

A − 2b f t f
A

≤ 0.5

(IS 9.3.1.2 (b))

For Rolled I-sections
=
M ndz 1.11M dz (1 − n ) ≤ M dz

(IS 9.3.1.2 (c))

if n ≤ 0.2 ,
 M dy ,
M ndy = 
(IS 9.3.1.2 (c))
1.56 M dy (1 − n )( n + 0.6 ) ≤ M dy , if n > 0.2

–

For Hollow Rectangular sections:

 1− n
=
M ndz M dz 
 1 − 0.5aw


 ≤ M dz


(IS 9.3.1.2(d))

 1− n 
=
M ndy M dy 
 ≤ M dy
 1 − 0.5a f 

(IS 9.3.1.2(d))

where
=
aw

af
=

–

A − 2bt f

≤ 0.5

(IS 9.3.1.2(d))

A − 2ht w
≤ 0.5
A

(IS 9.3.1.2(d))

For Hollow Circular Tube sections:
M
=
1.04 M dz (1 − n1.7 ) ≤ M dz
ndz

(IS 9.3.1.2(e))

M
=
1.04 M dy (1 − n1.7 ) ≤ M dy
ndy

(IS 9.3.1.2(e))

In all of the preceding cases, n is taken as
T
 ,
N  Td
=
n = 
Nd  P
,
 Pd

(b)

if N is tensile

(IS 9.3.1.2)
if N is compressive

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:
My
M
N
+
+ z ≤ 1.0
N d M dy M dz

(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 becomes zero.
(c)

For Channel, Double Channel, Double Angle, Angle, General, and Section Designer sections, combined axial force and bending is conservatively checked by taking a linear summation of the utilization ratios for
each force component as:
My
M
N
+
+ z ≤ 1.0
N d M dy M dz

(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 itself. So the program named the equations as 9.3.1.1(a) and 9.3.1.1(b) to distinguish 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 axial force and bending is conservatively checked by taking the linear summation
of the utilization ratios for each force component:
My
M
N
+
+ z ≤ 1.0
N d M dy M dz

(IS 9.3.1.3)

For Doubly Symmetric sections, the preceding equation is a representation of
the code-specified equation given here:
fx ≤

γ M0

(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 interaction equation is given by the following:

 M y   Mz 
N
+ 
 +
 ≤ 1.0
Nd
 M dy   M dz 
2

(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 details.

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 utilization ratios based on the following two interaction equations:
Cmy M y
M
P
+ Ky
+ K LT z ≤ 1.0
Pdy
M dy
M dz

(IS 9.3.2.2(a))

Cmy M y
C M
P
+ 0.6 K y
+ K z mz z ≤ 1.0
Pdz
M dy
M dz

(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,

M y, M z =

maximum factored applied bending moments about the yand 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),
K y = 1 + ( λ y − 0.2 ) ny ≤ 1 + 0.8ny

(IS 9.3.2.2)

K z = 1 + ( λ z − 0.2 ) nz ≤ 1 + 0.8nz

(IS 9.3.2.2)

K LT = 1 −

0.1λ LT ny

(CmLT − 0.25)

≥1−

0.1ny

(CmLT − 0.25)

(IS 9.3.2.2)

where,
n y , nz

ratio of actual applied axial force to the design axial strength
for buckling about the y and z axis, respectively, and

KL
λ y = 22
r22 π
KL
λ z = 33
r33 π

CmLT

fy
E
fy
E

(IS 7.1.2.1)

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 consideration.

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 itself. So the program named the equations as 9.3.2.2(a) and 9.3.2.2(b) to distinguish 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
M

ψM

Cmy, Cmz, CmLT
Two or More
Concentrated Loads or Single Concentrated
Case
Uniform Load
Load On Segment

Range

−1≤ψ≤1

(a)

0.6 + 0.4ψ ≥ 0.4

Linear moment diagram
Mh

ψ Mh

0 ≤ αs ≤ 1

α s =M s M h

End moment dominating M h ≥ M s

ψ Mh

− 1 ≤ αs ≤ 0

0 ≤ αh ≤ 1

Ms
α h =M h M s

Span moment dominating M s ≥ M h

− 1 ≤ αh ≤ 0

−1≤ψ≤1

(b)

0.2 + 0.8αs ≥ 0.4

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

−1≤ψ≤1

(e)

0.95 − 0.05αh

0.90 + 0.10αh

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
Cmy, Cmz, CmLT 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:
−ψ

My
M
T A
+
+ z ≤ 1.0
M d Z ec M dy M dz
Cmy M y
M dy

0.6 K y

+ K LT

Cmy M y
M dy

Mz
≤ 1.0
M dz

+ Kz

Mz
≤ 1.0
M dz

(IS 9.3.2.1)

(IS 9.3.2.2(a))

(IS 9.3.2.2(b))

where,
T

factored tensile force,

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 interaction equations in this section of the code of which none of them are numbered 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 capacity 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 described 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:
Vy

≤ 1.0

(IS 8.4)

Vz
≤ 1.0
Vdz

(IS 8.4)

Vdy

3.10

Checking the Maximum Effective Slenderness Ratio of a
Member
The maximum effective slenderness ratio, KL/r values of a beam, strut or tension 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.
K l K l 
Kl
= max  33 33 , 22 22  .
r
r22 
 r33

SI No.

Member

Maximum
Effective
Slenderness
Ratio (KL/r)

A member carrying compressive loads resulting from dead loads
and imposed loads

180

ii)

A member subjected to compression forces resulting from a combination with wind/earthquake actions only, provided the deformation 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

4.5

1.2DL + 0.5LL ± 2.5EL

(IS 12.2.3(a))

0.9DL ± 2.5EL

(IS 12.2.3(b))

Special Check for Column Strength
When P / Pd 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

Ordinary Concentrically Braced Frames (OCBF)
15B

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 P / Pd in columns due to prescribed loading combinations without
consideration of amplified seismic load is greater than 0.4, the axial compressive 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

Special Concentrically Braced Frames (SCBF)
4B

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 P / Pd in columns due to prescribed loading combinations without
consideration of amplified seismic load is greater than 0.4, the axial compressive and tensile strengths are checked in the absence of any applied moment and shear for the special seismic load combinations as described previously 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 accordance with to Table 3-3 (IS 12.8.4.1, 12.8.2.5). If this criterion is not satisfied, 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 message.

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

Ordinary Moment Frames (OMF)
12B

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 importance factor greater than unity (I > 1) (IS 12.10.1.1).
 When P / Pd in columns due to prescribed loading combinations without
consideration of amplified seismic load is greater than 0.4, the axial compressive and tensile strengths are checked in the absence of any applied moment and shear for the special seismic load combinations as described previously in the "Special Check for Column Strength" section of this chapter (IS
12.5.1).

4.6.5

Special Moment Frames (SMF)
10B

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 P / Pd in columns due to prescribed loading combinations without
consideration of amplified seismic load is greater than 0.4, the axial compressive 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

Design of Continuity Plates
20B

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.

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 principal 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

Design of Doubler Plates
21B

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
=
Vp

∑
n =1

M bn cos θn
− Vc .
d n − t 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 − t f
d = dc
With this assumption, Kv, τcr,e, λw, and τb are calculated. Then Vd is taken as
Vn = tb dctwc
If shear buckling does not control, τb becomes equal to f y

(IS 8.4.2.2)
3 (IS 8.4.1).

By using Vd = Vn γ m 0 , the required column panel zone thickness t p is found
as follows.

tp =

Vp γ m0
τb d c

The extra thickness, or the required thickness of the doubler plate is given as
follows:
t dp= t p − t w ,

where,

Joint Design

4-9

Steel Frame Design CSA S16-09

= Column and doubler plate yield stress

= Required column panel zone thickness

t fn

= Flange thickness of n -th beam

tdp

= Required doubler plate thickness

t fc

= 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 n -th beam connecting to column

θn

= Angle between n -th beam and column major direction

= Overall depth of column

M bn = Factored beam moment from corresponding loading combination
Vn

= Nominal shear strength of panel

The largest calculated value of tdp , 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 M p ) , or beam moments due to specified load
combinations involving seismic load (IS 12.11.2.2). For seismic design, V p
4 - 10

Joint Design

Chapter 4 - Special Seismic Provisions

is calculated using the equation given previously, except that M pb is taken
as 1.2 f y Z p 33 (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 thickness requirement:
t≥

− 2t fc ) + ( db − 2t fb )
90

(IS 12.11.2.4)

Here, t is taken as twc + tdp when the doubler plate is plug welded to prevent
local buckling. In such cases, tdp is increased if necessary to meet this
criterion. If the doubler plate is not plug welded to the web, t is taken as

twc and also as tdp for checking both plates. If twc cannot satisfy the criteria,
then a failure condition is declared. If tdp 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

Weak Beam Strong Column Measure
2B

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).

∑ M pc
≥ 1.2
∑ M pb

(IS 12.11.3.2)

where

∑ M pc = sum of the moment capacity in the column above and below
the beam centerline

∑ M pb = 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
nb

Rmaj =

1.2∑ M ∗pbn cos θn
n =1

M ∗pcax + M ∗pcbx

(IS 12.11.3.2)

For the minor direction of any column, the beam-to-column-strength ratio is
obtained as
nb

Rmaj
=

1.2∑ M ∗pbn sin θn
n =1

M ∗pcay + M ∗pcby

(IS 12.11.3.2)

where,
Rmaj

= Plastic moment capacity ratios, in the major directions of the
column

Rmin

= Plastic moment capacity ratios, in the minor directions of the
column

M ∗pbn

= Plastic moment capacity of n-th beam connecting to the column

θn

= Angle between the n-th beam and the column major direction

M ∗pcax , y = Major and minor plastic moment capacities, reduced for axial

force effects, of column above story level
M ∗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

P 
M ∗pc Z c  Fyc − uc 
=

Ag 


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
M ∗pb = Fyb Z b f mv

where,
Z b = Plastic modulus of beam
Zc

= Plastic modulus of column

Fyb = Yield stress of beam material
Fyc = Yield stress of column material
Puc = Axial compression force in a column for a given load
combination

Ag = Gross area of the column
f mv = 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 f mv is taken as follows:
f mv = 1 +

dc
where,
Lb

d c = Depth of column section, and
Lb = 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

Evaluation of Beam Connection Shears
23B

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:
V=

1.2CM pb
Lh

+ 1.2VDL + 0.5VLL

(IS 12.11.2.2)

where,

4 - 14

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

M pb

Plastic moment capacity of beam

Clear length of the beam

Joint Design

Chapter 4 - Special Seismic Provisions

VDL

Absolute maximum of the calculated beam shears at the
corresponding beam ends from the factored dead load only

VLL

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:
=
Vu

1.2CM pb
Lh

+ VDL + VLL

(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

Evaluation of Brace Connection Forces
24B

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, determined as 1.1 f y Ag (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, determined as 1.2 f y Ag (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 specialist 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 design 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 includes 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 calculation.
The following sections describe some of the typical graphical display, file output, 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 information 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 information 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 several 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



P-M stress ratio values with members
color-coded based on the ratio



P-M colors and shear stress ratio values



P-M ratio colors and no values



Continuity plate and doubler plate
thickness



Beam/column capacity ratios



Beam connection shear



Brace connection axial force

 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)



Identify the P-M failure



Identify the shear failure



Identify all failures

 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)

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 displayed 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 transformations 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 tables 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 Modify/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, holding and dragging the left mouse button to merge the split key to its original location.

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. Alternatively, 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 information 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 tolerance, number of decimal digits and so forth. The tables can be formatted, filtered 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 currently 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 program.
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 design 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. Alternatively, 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 demand/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 Overwrites 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 information includes the member ID, load combo and station identifications,
steel design sections, section properties, design combination forces, stress ratios 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 highlighted 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 Command 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 selected 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 Format-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 saving/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 saving/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 Bahadur 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 – Specification for Structural Steel Building, American Institute of Steel Construction, 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

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