CT15 SHS Welding Structural Hollow Sections

User Manual: Structural Hollow Sections Welding

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Corus Tubes

SHS welding
Structural & Conveyance Business

Contents
01

Introduction

Product specification

Welding practice

Manual metal arc welding

Semi-automatic welding

End preparation of members

Welding procedures and sequences

Fillet welds

Butt welds

Fabrication

Design of welds

Appendix 1 - Fit-up and lengths of intersection

Table 1 - Size of RHS and CHS bracings which can be

Table 2A - Length of curve of intersection of CHS bracing

Fitted to CHS main members without shaping

on a flat plate or RHS main member

Table 2B - Length of intersection of RHS bracing on a
flat plate or RHS main member

Table 2C - Length of curve of intersection of CHS bracing
on a CHS main member

Appendix 2 - Templates for profile shaping ends of CHS
bracing to fit CHS main member

Reference standards & documents

Introduction

Welding represents the major method
by which structural hollow sections are
joined. When considering welding, the
most essential requirement is that the
deposited weld should have
mechanical properties not less than
the minima specified for the sections
being joined.
In addition, because hollow sections are
welded from one side only, correctness of
fit-up of components, weld preparations
and procedures are also key factors.
In light of this, it is recommended that
welding parameters, consumables, etc.
are checked, prior to commencement of
full production, by conducting welding
procedure tests. Guidance on the most
appropriate tests can be found in EN 288
Part 1: Specification and approval of
welding procedures for metallic materials General rules for fusion welding.
Successful welding, however, is concerned
not only with materials and procedures but
also with the ability of the welding operator.
It is always advisable to use welders
qualified in accordance with the
requirements of EN 287 Part 1 or
alternatively BS 4872. The designer of
welded structures also has an important
part to play, since poor design/detailing
can produce welded joints that are
impossible or at least difficult to fabricate.
Welding is a subject which encompasses
the materials, types of joint, welding
conditions/positions and the required
quality or mechanical properties of the
finished joint. The recommendations made
in this publication are thus of guidance
towards good practice and should be used
in conjunction with other standards,
especially EN 1011*: Welding Recommendations for welding of metallic
materials, ENV 1090 and EN 29692.
* Superceeds BS 5135 which was withdrawn
March 2001.

SHS welding 1

Product specification
Corus Tubes produces four types of hollow section: Celsius® 275, Celsius® 355,
Hybox® 355 and Strongbox® 235.
Celsius® hot finished structural hollow sections are produced by the Corus Tubes Structural
& Conveyance Business. They are availble in two grades Celsius® 275 and Celsius® 355,
which fully comply with EN 10210 S275J2H and EN 10210 S355J2H respectively. All
Celsius® hot finished structural hollow sections have an improved corner profile of 2T
maximum. For full details see Corus Tubes publication CTO6.
Hybox® 355 and Strongbox® 235 cold formed hollow sections are produced by Corus
Tubes Cold Form Business. Hybox® 355 fully complies with EN 10219 S355J2H.
Strongbox® 235 is in accordance with the Corus Tubes publication CTO5. The chemical
composition and mechanical properties of these products, are given below.
Chemical composition

Specification
C % max
Si % max

Cold formed hollow sections
Strongbox® 235 Hybox® 355
TS 30 (1)
EN 10219 355J2H
0.17
0.22
0.55

Hot finished hollow sections
Celsius® 275
Celsius® 355
EN 10210 275J2H EN 10210 355J2H
0.20
0.22
0.55

Mn % max
P % max
S % max
Ni % max
CEV % t ≤16mm

1.40
0.045
0.045
0.009
0.35

1.50
0.035
0.035
0.41

(1)

1.60
0.035
0.035
0.45

Corus Tubes specification TS 30, generally in accordance with EN 10219 235JRH.

Mechanical properties

Specification
Tensile strength Rm N/mm2
t < 3mm
3 < t ≤ 40mm
Yeild strength Rehmin N/mm2
t ≤ 16mm
t > 16mm
Min Elongation %
Lo=5.65 √S0 t ≤ 40mm
Impact properties
Min Ave energy (J)
10 x 10 specimen
(1)

Cold formed hollow sections
Strongbox® 235
Hybox® 355
TS 30 (1)
EN 10219 355J2H

Hot finished hollow sections
Celsius® 275
Celsius® 355
EN 10210 275J2H
EN 10210 355J2H

340 min

510-680
490-630

430-580
410-560

510-680
490-630

235
-

355
-

275
-

355
345

24(2)(3)

20(2)(3)

27 @ -20ºC

Corus Tubes specification TS 30, generally in accordance with EN 10219 235JRH excluding
upper tensile limit and mass tolerance.

(2)

17% min for sizes 60 x 60, 80 x 40 and 76.1mm and below.

(3)

Valve to be agreed for t< 3mm

Note: For Strongbox® 235, reduced section properties and thickness applies.
All thicknesses used in the design formulae and calculations are nominal, except for
Strongbox® 235 which should use 0.9tnom or (tnom-0.5mm) whichever is the larger.

2 SHS welding

Welding practice

All Corus Tubes structural hollow sections are
made from steels of weldable quality. The
weldability of a steel is determined by the Carbon
Equivalent Value (CEV), which is calculated from
the ladle analysis using the formula
C + Mn + Cr+Mo+V + Ni+Cu
6
5
15
To maintain weldability the maximum CEV for
steel sections should not exceed 0.54%.
All Corus Tubes products are below this limit
(see table opposite)
All Corus Tubes test certificates state values for
the full 16 element range of the chemical analysis
and the determined CEV.
The welding practice for carbon and carbon
manganese steels is given in EN 1011-2.
Requirements are given for all ferritic steels,
except ferritic stainless steel, dependent on the
material grade and it's CEV. The most common
processes used with hollow sections are manual
metal arc (MMA) and the semi-automatic gas
shielded processes (MIG/MAG/FCAW).
Note - Where it is necessary to weld two different
grades of steel, the welding procedure for the
higher grade should normally be adopted.

SHS welding 3

Manual metal arc welding (MMA)

Manual metal arc welding (MMA) was
once the most commonly used welding
process for structural hollow section
construction, however the development
of the semi-automatic welding processes
(MIG/MAG/FCAW) has led to a decline in its
use except where restricted access and/or
site conditions prevail when MMA is still
extensively used.
Electrode selection should have regard to
the particular application, i.e. joint design,
weld position and the properties required to
meet the service conditions. Advice on
particular electrodes should be sought from
their manufacturer and, if required or
considered necessary, their performance
evaluated by weld procedure tests in
accordance with EN 288 Part 3.

4 SHS welding

All electrodes must be handled and stored
with care to avoid damage and electrodes
with damaged coatings should never be
used. Electrode coatings readily absorb
moisture and the manufacturer's
instructions regarding protection and
storage must be carefully followed to avoid
this. Where hydrogen controlled electrodes
are being used, these may require oven
drying immediately prior to use, using
drying procedures recommended by
the manufacturer.

Where impact properties of the weld are
important, or where structures are subject
to dynamic loading - such as, for example,
crane jibs and bridges - hydrogen controlled
electrodes should be used irrespective of
the thickness or steel grade being joined.
Where there are several steel grades in a
workshop it is advisable to use only
hydrogen controlled electrodes to avoid
errors. Welding operators must, of course,
be familiar with the techniques required for
using these electrodes.
Whilst EN 499 provides a classification
system for electrodes, electrode
manufacturers generally supply their range
of products by trade names. The following
is a guide to electrode designations to
EN 499 for use on various grades of
hollow section.
For Strongbox® 235:
Electrodes matching this grade may not be
available. User is recommended to use
guidance for S275J0 material or consult the
electrode manufacturer.

For Celsius® 275, Celsius® 355 and
Hybox® 355:
Depending on the application thickness
and service conditions, rutile or hydrogen
controlled electrodes to EN 499
designation: 'E 35 (or 42) 2 Rx Hx' (rutile)
and 'E 35 (or 42) 2 B H5' (low hydrogen)
can be used. Rutile electrodes have good
operability, a stable arc and are versatile
but, produce a high hydrogen input. In
cases of high restraint or high fabrication
stresses low hydrogen electrodes are to be
preferred. Prior to making a final selection
the user is recommended to discuss
requirements with the electrode
manufacturer.
Note - If the project requirements only
require the properties of S275J0H or
S355J0H material the electrodes
designated as E 35 (or 42) 0 Rx Hx and
E35 (or 42) 0 B H5 can be used.
For Sub-grades NLH and NH:
Only hydrogen controlled electrodes
(E 50 2 B H5) are recommended and care
should be taken to ensure that the

deposited weld has mechanical properties
not less than the minima specified for the
parent material.
For weather resistant steel to
BS 7668 grade S345GWH:
The choice of electrodes is restricted to
hydrogen controlled types which give the
deposited weld mechanical properties not
less than the minima specified for the parent
material, i.e. E 42 2 B H5. Because of the
weathering properties of S345GWH it is
also necessary to consider the weathering
properties and the colour match of the weld
metal if the steelwork is to be an
architectural feature. In cases where the
dilution of the weld metal is high sufficient
weathering and colour matching properties
will be imparted to the weld metal even
when using a plain carbon steel electrode.
This will normally be the case when welding
S345GWH thicknesses up to and including
12mm. With thicknesses in excess of
12mm the use of electrodes containing
2-3% nickel (E 42 2 2Ni (or 3Ni) B H5)
should be considered, either for the
complete weld or for the capping runs only.

SHS welding 5

Semi-automatic welding

Semi-automatic welding employing
a gas shield with a bare solid metal wire
or flux and metal cored wire may be
used where suitable applications exist.
The process is capable of depositing weld
metal with a low hydrogen content and is
suitable for welding all material grades.
The popular wire sizes are 1.0 and 1.2mm
diameter, although 0.8mm diameter bare
wire can be used to advantage on light
sections and for root runs without backing.
Bare wires should conform to the
requirements of EN 440. Flux and metal
cored wires should conform to EN 758.
Shielding gases used include CO2 ,
argon/CO2 and argon/oxygen mixtures.
The gas used will depend on the material
compatibility and physical properties, the
mode of operation, joint type and thickness.
The characteristics of the process depend
on the mode of metal transfer from the
electrode to the weld pool, the common
modes of transfer being "dip" and "spray".
Low current "dip" transfer is used for
welding lighter structural hollow sections
and for positional welding whilst the high
current "spray" mode of metal transfer can
be used for downhand welding of
thick sections.
Semi-automatic gas shielded welding with
bare wire has the advantage of continuous
weld deposition which, by virtue of the gas
shield, does not require deslagging
between subsequent runs. This results
in faster welding times and hence can
produce cost reductions in the
fabrication process.
The electrode wire and gas are deposited at
the weld location through a nozzle. Hence,
sufficient access to the weld area to present
the nozzle at the required angle is needed.
Where access is severely restricted it may
be appropriate to change the details or to
use the manual metal arc process.

6 SHS welding

Wire electrode

Shielding gas

Gas shield

SHS welding 7

End preparation of members

Cutting/sawing
The first stage in any end preparation of members
is cutting.
Circular Hollow Sections (CHS) and Rectangular
Hollow Sections (RHS) may be cut by any of the
usual steel cutting methods. The end preparation
may involve either square cutting, mitre cutting,
profiling or crimping.
Power hacksaws
Power hacksaws, which are available in most
workshops, are very useful for "one off" and small
quantity production and have the advantage that
they can often be used for the larger sizes, which
could require more expensive equipment.
The utility of these saws is greatly improved if they
can be adapted for mitre as well as straight 90°
cutting. Their main drawback is their relatively
low speed of operation.
Friction-toothed and abrasive disc
cutting machines
High-speed rotary friction-toothed cut-off
machines and abrasive disc cutting machines
are the most widely used for cutting SHS.
The choice is largely one of initial cost, plus blade
life and the resharpening of the friction-toothed
blade, compared to the life of the abrasive wheel.
Friction-toothed machines
These machines are fast in operation and give a
good finish relatively free from burrs. The alloy or
mild steel cutting discs have peripheral serrations
or teeth, depending upon type, which serve a
two-fold purpose - first to induce localised heat
to the workpiece by friction and then to remove
the hot particles under the forward motion of
the cutter.

8 SHS welding

The capacity of friction machines is usually limited
to the smaller sections, although machines are
available for cutting quite heavy sections at the
expense of a rather high capital outlay. Where
large cross sections are to be cut, the available
power needs to be high to prevent slowing down
of the disc.
Few of these machines incorporate a swivel head
mounting to allow mitre cuts and hence for these
cuts the workpiece must be angled.
Abrasive disc cutting machines
As with the friction toothed machines, the
abrasive disc type are fast in operation and their
use is usually limited to the smaller sections.
Their capacity is not as wide as for friction
machines, probably due to the more specialised
type of blade required and the difficulties
associated with their manufacture in the
larger diameters.
Some of the abrasive machines available,
however, do provide a swivel cutting head for
carrying our angle cuts without the need for
moving the workpiece, although the maximum
angle does not usually exceed 45°. In the larger
machines the blades are metal centred to
minimise wheel breakage.

Bandsaws
These are of more general use and, cost for cost,
capable of tackling a larger range of sizes than the
disc cutters. They are therefore more useful for
the jobbing shop where the variety of section
shapes and sizes is extensive but where speed of
cutting is not so essential. Blades are relatively
cheap, fairly long lasting and if broken can very
often be repaired by the use of a small
welding/annealing machine. Bandsaws are safe
to use if the blade is adequately guarded and
cutting oil is used to control the swarf.
Flame cutting
Hand flame-cutting may be used for cutting any
structural hollow section, but this method is
mostly used for site-cutting, for cutting the larger
sized sections and for profile-cutting of ends.
A ring fixed to CHS or a straight-edge for RHS
may be used as a guide for the cutting torch, thus
producing a clean cut and reducing subsequent
grinding.

Grinding or chamfering
When required this is usually done with a portable
grinder, but pedestal grinders can be adapted for
dealing with short lengths by fitting an adjustable
guide table.
Machining
Turning or parting-off in a lathe is generally too
slow for ordinary structural work. It is more
commonly used for end preparation for high
quality full-penetration butt-welds for pressure
services. Horizontal milling also tends to be too
slow, although where a great deal of repetition is
involved, gang-millers with high-speed cutters
have been used successfully for shaping the ends
of hollow sections.
An end mill of the same diameter as the CHS
main member can be used for cutting and
shaping the ends of smaller branches. Where
these branches are to be set at 90° this method
offers the advantage of being able to cut two
ends at the same time.

Crawler rigs are available which can be fixed
to the section to give semi-automatic
straight cutting.
Where a number of ends require identical profileshaping by hand flame-cutting, templates can be
used to reduce individual marking off time.
Machines are available which will flame-cut CHS
and profile-shape the ends to any combination of
diameters and angles within their range, and will
also simultaneously chamfer the ends for buttwelding if necessary. The cost of these machines
varies considerably, being controlled mainly by the
range of sizes they cover and the complexity of
the operations they can perform.
See section on fabrication for any pre-heat
requirements.

SHS welding 9

End preparation of members

Not to exceed
2mm

Profile shaping

Straight cutting

Shearing, punching and cropping
Shaping the end of a hollow section by
cropping through one wall at a time by
means of a suitably shaped tool in a punch
or fly-press or a nibbling machine is
acceptable, providing the section is not
distorted in the process.

Where the gap exceeds 2mm, some
method must be employed to bring the gap
within this limit.

By reason of possible eccentricity and
distortion, hollow sections cut by means of
a punch or shears are not recommended
for load bearing members. Hollow sections
with the ends cut and shaped
simultaneously by means of a punch or
"crop-crimped" (cut and crimped by means
of a press, in one operation) are, however,
often used for light fabrications.

Note: Whichever method is used bracings
should not ordinarily intersect the main
members at angles of less than 30° to allow
sufficient accessibility for welding at
the crotch.

Straight cutting
In accordance with EN 1090-4, “Straightcut” structural hollow sections may be fillet
welded to any suitable flat surface such as
RHS, or to any suitable curved surface
providing the welding gap caused by such
curvature does not exceed 2mm. Details of
the size combinations where a bracing can
have a straight cut and still fit up to a CHS
main member without exceeding the 2mm
weld gap limit are given in Appendix 1
Table 1.

10 SHS welding

The two methods most generally used are:
profile shaping (or saddling) and crimping
(or part flattening).

Profile-shaping or saddling
This is the process of shaping the ends
of an SHS member to fit the contour
of a curved surface such as a CHS
main member.
Machines are available which will flame-cut
and profile-shape the ends of CHS to the
required combination of diameter and
angle. The profiled ends may also be
chamfered at the same time if a butt welded
connection is required.

For small quantity production hand
flame-cutting is generally employed and
Appendix 2 shows a method of setting out
templates which is suitable for most work.
Templates for marking-off may be of oiled
paper, cardboard or thin sheet metal,
depending on the degree of permanence
which is required.

2mm
max

Crimping or part-flattening

Crimping or part-flattening
Some saws and shears can be fitting with
crimpers for carrying our this simple
operation: alternatively, a small press or an
internal spacer may be used to limit the
amount of flattening. In either case the
welding gap caused by the chord curvature
should not exceed 2mm for fillet welding.
Crimping or part-flattening is normally
restricted to CHS and to a reduction of
approximately one-third of the original
diameter of the CHS branch member.
The maximum size of bracing that can be
fitted to a CHS main chord to maintain a
maximum gap of 2mm is given in Appendix
1 Table 1.

Partial profiling

Partial profiling
When full width bracing members are
welded to an RHS main member with large
corner radii partial profiling may be
necessary to ensure that the minimum fit-up
tolerances for either a fillet weld or a butt
weld are achieved.
NB: This condition can arise when using
cold formed hollow sections.
See also Fabrication cold form RHS corner
regions page 22.

SHS welding 11

Welding procedures and sequences

The four principal welding positions, which
are used for SHS, are suitable for either butt
or fillet welding.

Electrode

360° Flat rotated
(Butts PA* and fillets PB*)
The member is rotated through 360º in an
anticlockwise direction. A downhand (flat)
weld is made with the electrode always
adjacent to the crown of the member.

Rotated 360º

Horizontal-vertical
(Butts PC* and fillets PB* or PD*)
This method is used when the member
cannot be moved and is in an upright
position.

Fully positional
Vertical-upwards (PF*)
This method is used on the comparatively
rare occasions when the member or
assembly cannot be moved.

3
1

2
2

2
4

12 SHS welding

180º Vertical upwards (PF*)
This is a commonly used method and is
particularly suitable for planar lattice
construction. All the welds are made on the top
side and then the whole panel is turned over
through 180º and the remaining welds
completed.

Panel turned
180º

Panel turned
180º
2

Note:
1.When using the above sequences for
welding RHS, the start/stop weld positions
should be of the order of five times the
section thickness (5 t) from the corners.

2.When using the above sequences for
welding CHS bracings to a main or chord
member, the start/stop weld positions should
not be at the positions marked with an 'X'
on the adjacent sketch.

* In the weld sequence descriptions shown on
pages 12 and 13 the details in brackets refer to
the designations given in prEN 13920-2 for
welding positions.

SHS welding 13

Fillet welds

Apart from the special case of end to end
connections where butt joints, developing
the full strength of the sections, are usually
desirable, fillet welding provides the
economic answer to most of the joints in
static structures.

Branch connection details fillet welds
The following figures show the basic
conditions which are encountered when
making fillet welds on SHS branch
members : L = Leg length.

A fillet weld can be specified by its throat
thickness and/or leg length and the
deposited weld shall be not less than the
specified dimensions.

Special note: The gaps shown in the
above details are those allowed by
ENV 1090-4 for normal fillet welds. In the
case of small size fillet welds below 5mm
and, especially for crimped or straight cut
branch members to circular chords,
consideration should be given to increasing
the minimum leg length required by 2mm
to ensure adequate strength is achieved.

b1
d1

A,B

D
A,B
θ

θ
h0

This edge prepared
as a buttweld

L
2mm max

2mm max

θ = 30º to 60º

2mm max

L
L

Where b1< b0

θ = 60º to 90º

Detail at C
2mm max
Edge preparation
may be required
for sharp corners
Where b1= b0
L

Detail at A,B

2mm max

Detail at D

14 SHS welding

For smaller angles
full penetration is not
intended provided
there is adequate
throat thickness

Fillet and fillet-butt welds
Fillet welds joining SHS to flat surfaces
such as plates, sections, or RHS main
members are self explanatory, but some
confusion has arisen in the past over the
terms “fillet” and “fillet-butt” where
structural hollow sections are welded to
CHS main members. The terms describe
the welding conditions which apply when
various size ratios of bracing to main
member are involved.

The following shows two bracings, of the
same size, meeting main members of
different sizes. In both cases welding
conditions at the crown are similar, so for
the same loads identical fillets would be
used. At the flanks, however, conditions
differ. The curvature of the larger main
member continues to give good fillet weld
conditions while the curvature of the
smaller main member necessitates a butt
weld. The change from fillet to butt weld
must be continuous and smooth.

For calculating weld sizes, both types are
considered as fillet welds. The fillet-butt
preparation is used where the diameter of
the bracing is one third or more of the
diameter of the main member.

SHS welding 15

Butt welds

Weld reinforcement

Throat
thickness

Backing member

General
The end preparation for butt welding
depends on many factors including the
thickness of the section, the angle of
intersection, the welding position and the
size and type of electrode employed.
Where full penetration has been achieved
and the correct electrodes for the type of
steel have been employed, butt welds in
SHS may be regarded as developing the
full strength of the parent metal.
Butt welds may be used regardless of the
thickness of the section or, in the case of
CHS, of the ratio between the diameter of
the bracing and that of the main member.
Where multi-run butt welds are required the
root run or runs should be made with
3.25mm diameter or smaller electrodes,
using one of the sequences shown on
pages 12 or 13 according to the technique
employed.
The finished weld must be proud of the
surface of the parent metal by an amount
not exceeding ten per cent of the throat
thickness of the weld. This reinforcement
may be dressed off if a flush finish is
required.

End-to-end butt welds
It is permissible to butt weld hollow
sections end-to-end up to and including
8.0mm thick without end preparation, i.e.
square butt weld (with backing), but in
general an upper limit of 5mm is
recommended to avoid large weld
deposites and associated shrinkage and
distortion.
Although specifications permit end-to-end
butt welds to be made without backing, the
use of backing members is recommended,
as they help in lining up the sections as well
as assisting in ensuring a sound root run.
In general, backing members are necessary
for full penetration butt welds.
The following details have, unless noted,
been taken from EN 29692. The end
preparation shown are those normally used
for joining two structural hollow sections
of the same size and thickness. For joining
sections of different thicknesses see
page 18.
For material over 20mm thick, welding trials
should be carried out to establish the most
suitable procedure.

Square butt weld - without backing

Weld detail

16 SHS welding

Thickness T

Gap b

≤4

≈T

Square butt weld - with backing

Weld detail

Gap b

Thickness T
min.

max.

3-8

Single V - with or without backing

Weld detail

Thickness of
root face c

Gap b

Thickness T
min.

max.

min.

max.

Up to 10

40º - 60º
c
T
b

Single V - with backing: not included in EN 29692

Weld detail

Thickness of
root face c

Gap b

Thickness T

min.

max.

min.

max.

Up to 20

2.5

60ºmin
c
T

60º

Mitred butt welds: ENV 1090-4
For constructions such as bowstring
girders, mitred butt welds are often
used, instead of being cut square the
end is cut at an angle equal to half
the mitre angle. Backing members
for mitred butts have to be specially
made to suit the mitre.

60º
Mitre angles

SHS welding 17

Butt welds

Thickness difference
up to 1.5mm

Thickness difference > 1.5mm but ≤ 3mm

Slope not to exceed 1 in 4

Sections of different thicknesses:
ENV 1090-4
When SHS of different thicknesses are butt
welded end-to-end the transition between
the two thicknesses should be as smooth
as possible, especially for dynamic
structures. The strength of such a weld
is based on that of the thinner section.
For any given external size of hollow
section the change in wall thickness occurs
on the inside of the section. Differences
in thickness may be dealt with as follows:
No special treatment is required if the
difference does not exceed 1.5mm.
Differences not exceeding 3mm may be
accommodated by making the backing
member to fit the thinner section, tacking
it in position, locally heating it and dressing
it down sufficiently to enter the
thicker section.

Thickness difference
over 3mm

Backing members:
ENV 1090-4
Backing members must be of mild steel
with a carbon content not exceeding
0.25% and a sulphur content not
exceeding 0.060% or of the same material
as the parent metal. For CHS they are
usually formed from strip 20 to 25mm wide
and 3 to 6mm thick, with the ends cut on
the scarf to permit adjustment. They are
sprung into position inside the section and
are tack welded to the fusion face to hold
them in place.
Backing members for RHS are usually
formed from strip 20 to 25mm wide and
3 to 6mm thick, in two pieces, bent at
right angles and tacked in position.

Alternatively, lay down the first root run
round the thinner section and dress down
the backing member while it is still hot.
It may be necessary to mitre the corners by
hacksaw in some cases.
D+

Differences in thickness exceeding 3mm
necessitate the machining of the bore to
enable the backing member to fit snugly.
The machined taper should not exceed
1 in 4.

D-

18 SHS welding

Flat plate and branch connections
Although seldom necessary to meet design requirements butt welds can be used for such joints.
The two basic conditions are: Flat plate vertical - SHS horizontal and horizontal-vertical butt welds.
Flat Plate Vertical - SHS Horizontal
A typical example of this condition could be a flange plate welded to SHS. For most general work the end
preparation shown for a single bevel without a backing member is suitable, but where it is required to ensure
complete penetration a backing member should be used.
Single bevel - without backing

Weld detail

Thickness of
root face c

Gap b

Thickness T
min.

max.

min.

max.

Up to 20*

35º - 60º

T
c
b

* EN 29692 max 10
Single bevel - with backing - not included in EN 29692

Weld detail

Thickness of
root face c

Gap b

Thickness T

min.

max.

min.

max.

Up to 20

421/2º ± 21/2º

T
c
b

Horizontal-vertical butt Welds
Where SHS are in a vertical position and cannot be moved for welding, a double bevel form of
preparation is used. The weld face of the upper member is bevelled at 45° and that of the lower
at 15°. The weld gap may be adjusted to suit welding conditions. Backing members are strongly
recommended for joints of this type.

Double bevel - with backing - not included in EN 29692

Weld detail

Thickness of
root face c

Gap b

Thickness T

min.

max.

min.

max.

Up to 20

2.5

Upper
section
45º

15º
Lower
section

b
c
T

SHS welding 19

Butt welds

T
C

D
A, B
θ
d0

D
A, B
θ

Branch connections to structural
hollow section main members:
ENV 1090-4
If the main member is a circular hollow
section, then the angle of intersection
between the bracing and the surface of the
main member changes from point to point
around the perimeter of the bracing. The
basic preparations used give, as far as
possible, a constant 45º single bevel
between the weld face of the bracing and
the surface of the main member.

20 SHS welding

T
T
1 to 2mm

1 to 2mm

2 to 4mm

max 2mm

H
H
d1< 2d0/3

d1≥ 2d0/3
2 to 4mm

Detail at A,B for CHS

Detail at C

T
1 to 2mm

1 to 2mm

1 to 2mm
For < 60º a
fillet weld detail
(see detail at D
page 14) is preferred.

20º to 25º

H
2 to 4mm
Where b1< b0

2mm max.
Where b1=b0

2 to 4mm
Detail at D

Detail at A,B for RHS

= 60º to 90º

In all cases H ≥ T

Note: The angle of intersection θ of the
axes of the hollow sections should not be
less than 30° unless adequate efficiency of
the junction has been demonstrated.

SHS welding 21

Fabrication
General
While Structural Hollow Sections are light,
strong and graceful, there is sometimes a
tendency for fabricators, not familiar with
their use, to over weld. This is a bad
practice; it spoils the appearance of the
structure and tends to distort it as well as
adding unnecessarily to the welding costs.
Welds should be the minimum size
commensurate with the load to be carried
and the conditions of working.
Even when the weld sizes have been
correctly specified there are two common
causes of over welding during fabrication
and care should be taken to avoid them.
These are:
a) Fillet welds with too large a throat
thickness and/or leg length.
b) Butt welds with excessive reinforcement,
this should be limited to 10% of the
section thickness.
Poor "fit-up" of structural members can also
increase welding and rectification costs.
Whilst it is not necessary to have "machine
fits" time spent at the preparation and
assembly stages is usually amply repaid at
the welding stage.
Cold formed RHS corner regions
EN1993-1-1: Annex K: Table A4 restricts
welding within 5t of the corner region of cold
formed square or rectangular hollow section
chord members unless the steel is a fully
killed (A1≥ 0.025%) type.
Both Corus Tubes Strongbox® 235 and
Hybox® 355 meet the fully killed
requirements and can be welded in the
corner region unless the thickness is
greater than 12mm when the 5t restriction
applies.
Preheating for flame cutting
Preheating for flame cutting or gouging is
usually not required for Strongbox® 235 or
Celsius® 275 materials. However, a
minimum preheating temperature of 120ºC
should be used when either the ambient
temperature is below 5ºC or when Celsius®
355, Hybox® 355 and S460N grades over
13mm thick are being flame cut.
Preheating for tacking and welding
The temperature of any grade of material
prior to welding should not be less than 5ºC.

22 SHS welding

To establish the need for preheat and the
required preheat temperature EN 1011-2
should be consulted. The requirement for
preheating is dependent upon the variables
listed below:
Grade/composition of the section
e.g. it's CEV.
Combined thickness of the joint to
be welded.
Welding process parameters.
(Amperage, Voltage & travel speed)
Hydrogen scale of the process and
consumables.
If required, preheating should be applied to
a distance of 75mm either side of the joint to
be welded and checked using a suitable
temperature indicating device, e.g.
indicating crayon or contact pyrometer.
For Celsius® 275 and Strongbox® 235:Further preheat is not generally required.
For Celsius® 355 and Hybox® 355:Further preheat is generally not required with
sections up to 13mm thick for fillet welds
and up to 20mm thick for butt welds.
A minimum pre-heat temperature of 125°C
is required when fillet welding sections over
13mm thick and butt welding sections over
20mm thick.
For Sub-grades NH and NLH:No further preheat is required with sections
up to 8mm thick for fillet welds and up to
12mm thick for butt welds. A minimum preheat temperature of 175°C is required when
fillet welding sections over 8mm thick and
butt welding sections over 12mm thick.
For Grade S345GWH:The recommendations for Celsius® 355
apply.
Tack welds
Particular attention should be paid to the
quality of tack welds and they should be
deposited by qualified welders. The throat
thickness of tack welds should be similar
to that of the initial root run. The minimum
length of a tack weld should be 50mm,
but for material less than 12mm thickness
should be four times the thickness of the
thicker part being joined. The ends of the
tack welds should be dressed to permit
proper fusion into the root run.

Special notes:
Tack welds must not be applied at corners.
Backing members must always be tack
welded to the root face, never internally.
Jigs and manipulators
The shapes and close dimensional
tolerances of SHS make them very suitable
for jig assembly and the use of simple jigs
and fixtures is recommended wherever
possible.The strength and stiffness of SHS
usually permit them to be assembled and
tacked in a jig and then moved elsewhere
for welding, thus freeing the jig for further
assembly work. Manipulators, other than
supporting rollers for 360° rolling welds are
seldom required for general work.
The vast majority of work can be planned
using the 180° vertical-up technique.
Welding sequence
The usual practice in the fabrication of
panels and frames from SHS is to work
to open ends. That is to start welding in
the middle of a panel and work outwards
on alternate sides to the ends. This tends
to reduce distortion and avoid
cumulative errors.
Flange joints are usually associated with
close length tolerance and it is good
practice to first complete all the other
welding before fixing and welding on the
flanges as a final operation.
Weld distortion and shrinkage
Provided the joints have been well prepared
and assembled and the welding sequence
has been correct, distortion will be kept to a
minimum and rectification will not be a
major problem. It is a common mistake to
make bracing members a tight fit. A small
allowance should be made for shrinkage.
Flanges are sometimes clamped to heavy
“strongbacks” approximately twice the
thickness of the flange, to prevent distortion
during cooling. Weld shrinkage depends on
many factors, but a useful approximation is
to allow 1.5mm for each joint in the length
of a main member.
Welding conditions
Wherever possible, welding should be
carried out in workshops under controlled
conditions using suitably qualified welding
procedures. The surfaces to be joined
should be free from rust, oil, grease, paint

or anything which is likely to be detrimental
to weld quality. Special attention should be
given to cold formed hollow sections as
these are normally supplied with a corrosion
inhibitor/oil preparation applied to the steel
surfaces. When using the so called "weldthrough" primers, care should be taken to
avoid welding defects by ensuring these are
applied strictly in accordance with
manufacturer's recommendations.
Where site welding is required, additional
precautions should be taken to protect the
workpiece from adverse weather
conditions, i.e. damp and low temperatures.
Inspection of welding
In addition to visual examination for
dimensional inconsistencies and surface
breaking weld defects, the Magnetic
Particle and Dye Penetrant Inspection (MPI
& DPI) techniques are most commonly used
for SHS welds. For critical applications
these may also be supported by the use of
ultrasonic or radiographic inspection for
sub-surface defects.
Prior to undertaking any inspection it is
essential to establish the criteria on which
welds are accepted or rejected. Welding
repairs can significantly increase fabrication
costs and may lead to excessive distortion,
restraint and in the most severe cases
scrapping of the component or structure.
Hazards from fumes
When subjected to elevated temperatures
during welding or cutting, fumes will be
produced which may be injurious to health.
Good general ventilation and/or local
extraction is essential. When welding
galvanised, metal coated or painted
material care should be taken to ensure that
threshold limits are not exceeded and,
where possible, it is recommended that
coatings are removed local to the area to be
welded.

weld. Where SHS are aluminium sprayed
before fabrication, a distance of 75mm
around the welding position should be
left clear.
Repair of metal coatings at weld area
The completion of the protection at welds
on structures fabricated from either hot
dipped galvanised or aluminium/zinc
sprayed tubes can be satisfactorily
achieved by metal spraying. The sprayed
metal coating should be at least 130µm
thick. To ensure good adhesion of the
sprayed metal on the weld it is necessary to
grit blast or alternatively remove all welding
slag with a pneumatic needle pistol or by
hand chipping and preheat the weld area to
a temperature of 150°C to 350°C.
Due to the roughness of the parent coating
on aluminium/zinc sprayed tubes, this
method of weld protection gives a firm
bond at the overlap with the parent coating.
With hot dip galvanised SHS there is less
adhesion of the sprayed zinc at the overlap
with the parent coating. It is therefore
advisable to seal the whole of the sprayed
coating, including at least 25mm of the
parent hot dip galvanised coating, with zinc
rich paint. Coatings applied in this manner
ensure that the protection at the weld is as
good as the parent coating.
For galvanised coatings a less satisfactory
but more convenient method, which may
be acceptable for mildly corrosive
environments, is to clean the weld area
thoroughly and apply two or three coats of
a good quality zinc rich paint to give a
coating thickness of about 130µm.

Welding of galvanised and
metal coated SHS
There should be no difficulty in welding
galvanised or zinc-coated hollow sections,
but because of the fumes given off when
the zinc volatises, the operation must be
carried out in a well ventilated area.
The correct welding procedure is to use
a back-stepping technique; volatising the
galvanised coating with a lengthened arc
for 50mm then coming back and laying the

SHS welding 23

Design of welds
General
A weld connecting two hollow section members together should normally
be continuous, of structural quality and comply with the requirements of the
welding standard EN 1011 and ENV 1090-4 and the appropriate application
standard. The following design guidance on the strength of welds is based
on the requirements of BS 5950-1:2000 and ENV 1993:Part 1.1.
Fillet welds
Pre-qualified fillet weld size
According to ENV 1993-1-1:1992/A1:1994 : Annex K: Section K.5. for
bracing members in a lattice construction, the design resistance of a fillet
weld should not normally be less than the design resistance of the member.
This requirement will be satisfied if the effective weld throat size (a) is taken
equal to (α t) as shown in table 3, provided that electrodes of an equivalent
grade (in terms of both yield and tensile strength) to the steel are used.
Steel grade

Minimum throat size
Minimum throat size, a (mm)
a (mm)
UK NAD: γ Mw =1.35 Mj =1.1

Celsius® 275

0.87 t

0.94t

Celsius® 355

1.01 t

1.09t

Strongbox®

0.84 t

0.91t

235

1.01 t

Hybox® 355

1.09t

where t = bracing member thickness and = 1.1

1.25

Table 3 : Pre-qualified weld throat size

The criterion above may be waived where a smaller weld size can be justified
with regard to both resistance and deformational/ rotational capacity, taking
account of the possibility that only part of the weld's length may be effective.
General design of fillet welds
The design capacity of a fillet weld, where the fusion faces form an angle of
not more than 120º and not less than 30º is found from the multiplication of
the weld design strength (pw), the effective weld throat size (a) and the
effective weld length (s).
Weld design capacity = pw x a x s
If the angle between fusion faces is greater than 120º, for example at the toe
of an inclined bracing, then a full penetration butt weld should be used.
If the angle is less than 30º then adequacy of the weld must be shown.
Weld Design Strength (pw)
The values of the weld design strength pw (N/mm2 ) using covered
electrodes to EN 499 are given in BS 5950 and are shown in table 4.
Weld design strength, pw, for
EN 499 Electrode designation

Steel grade

E 35 2 xxxx

E 42 2 xxxx

Celsius® 275

220

Celsius® S355

220

250

Strongbox®

187

220

250

235

Hybox® S355
Table 4 : Weld design strengths

24 SHS welding

Effective weld throat size (a)
The effective throat size (a) is taken as the perpendicular distance
from the root of the weld to the straight line joining the fusion faces,
which lies within the cross section of the weld, but not greater than
0.7 times the effective weld leg length (L).
Where the fusion faces are between 30º and 120º the effective weld
throat size is calculated from the effective leg length by using the
reduction factor (fr), given in table 5, such that :
Effective weld throat size, a = fr x L

Angle ψ in degrees
between fusion faces

Reduction factor
(fr)

30 to 90

0.70

91 to 100

0.65

101 to 106

0.60

107 to 113

0.55

114 to 120

0.50

Table 5 : Throat size reduction factors

Weld design capacities per millimetre run of weld are given in table
6, they have been calculated from (a x pw).

Weld effective
throat size,
a mm

Steel grade
S235 with
E35 2 xxxx
electrodes
kN/mm run

Steel grade
S275J2H with
E 35 2 xxxx
electrodes,
kN/mm run

Steel grade
S355J2H with
E 42 2 xxxx
electrodes,
kN/mm run

0.56

0.66

0.75

0.88

1.00

0.94

1.10

1.25

1.12

1.32

1.50

1.31

1.54

1.75

1.50

1.76

2.00

1.68

1.98

2.25

1.87

2.20

2.50

Table 6 : Weld design capacity per unit length

Effective weld length(s)
The effective weld length for design will depend on the following
1. The actual length of the intersection. This will depend upon the
angle of intersection and the type of surface being welded to,
e.g. flat or curved. Lengths of curves of intersections are given
in Appendix 1, tables 2A, 2B and 2C.
2. The effectiveness of the actual length of intersection. Generally
connections to relatively thin flat surfaces, such as lattice
bracings to the face of an RHS will be less than fully effective,
whilst those to a thick plate or a curved surface are more likely
to be fully effective.

SHS welding 25

Design of welds

Joints with CHS chords
For joints with CHS chord members the weld effective throat size
can be determined using a calculated effective bracing thickness,
teff as shown below.
Assuming that the bracing member capacity, Nmem is required
to be equal to the joint capacity, Njoint , calculated from
ENV1993-1-1:1992/A1:1994. Then Njoint = Nmem = π t (d-t) fy /103
d/t is generally about 20, hence (d-t) = 0.95d and has a top limit in
ENV1993 of d/t ≤ 50
Hence the effective bracing thickness,
3
335 Njoint
teff = Njoint x 10
————— = ———— but with teff ≥ d/50
d fy
0.95 π d fy

Using the prequalified weld throat thickness factors (α) given in
table 3, the minimum throat sizes becomes α teff, see table 7.
For CHS joints with moments and axial loads
Napp
Mxapp
Myapp
replace Njoint in the above with ( ————— + ———— + ———— ) A
Zy
A
Zx
where A, Zx and Zy are the nominal section properties.
α factor

Effective bracing thickness,
teff = higher value of

Minimum weld throat thickness,
a mm = higher value of

Celsius® 275

0.94

(1.22 Njoint / d) and (d / 50)

(1.15 Njoint / d) and 0.94(d / 50)

Celsius® 355

1.09

(0.94 Njoint / d) and (d / 50)

(1.02 Njoint / d) and 1.09(d / 50)

Strongbox® 235

0.91

(1.43 Njoint / d) and (d / 50)

(1.30 Njoint / d) and 0.91(d / 50)

Hybox®

1.09

(0.94 Njoint / d) and (d / 50)

(1.02 Njoint / d) and 1.09(d / 50)

Yield strength,
fy N/mm2

355

Table 7 : Minimum Weld Throat Size for CHS Chord Joints

Joints with RHS chords and either two bracings with
a gap or one bracing
The weld effective lengths are based to a great extent on the
bracing effective periphery determined during the calculation of the
static capacity of welded lattice type joints. The effective peripheries
for bracing connections to RHS chord members are given in
ENV1993-1-1: 1992/A1:1994 and are shown below.

θi

The weld effective length, s, for K- or N-joints with a gap between
the bracings and predominantly axial loads can be taken as :

s = [(2 hi / sin θi ) + bi ] for θi ≥ 60º and
s = [(2 hi / sin θi ) + 2bi ] for θi ≤ 50º
for angles between 50º and 60º linear interpolation should be used.
For T-, Y- and X-joints with predominantly axial loads a conservative
estimate of the weld effective length, s, is given by
s = [2 h i / sin θi ] for all values of θi

bi
hj

Joints with RHS chords and overlapping bracings
The weld effective length, s, for the overlapping bracing of K- or
N-joints with overlapping bracings and predominantly axial loads
can be taken as

26 SHS welding

s = 2hi + bi + be(ov)

for overlaps ≥ 80%

s = 2hi + be + be(ov)

for overlaps ≥ 50% < 80%

s = (Ov/50)2hi + be + be(ov)

for overlaps ≥ 25% < 50%

θi
θj

with be(ov) =

10 fyj tj
—— ——
bj /tj fyi ti

10 fy0 t0
be = —— —— bi
b0 /t0 fyi ti
and

bi but ≤ bi

but ≤ bi

Ov = percentage overlap = q sinθi / hi x 100

The weld effective length, s, for the overlapped bracing can be taken as
being the same percentage of the actual weld length as that for the
overlapping bracing, i.e.
soverlapped = soverlapping (hj + bj)/(hi + bi) but ≤ 2 (hj/sinθj + bj) - bi
because the hidden part of the weld need not be welded if the vertical
components of the bracing loads do not differ by more than 20%
For RHS joints with moments and axial loads
the required weld throat thickness can be found from table 6 using the
stress in kN/mm found from
Mxapp
Myapp
Napp
——— + ——— + ———
A
Zx
Zy
where A, Zx and Zy are the bracing area and section modulii reduced
where appropriate for the ineffective widths.

Fillet weld design examples
All of the joint capacities quoted in these examples have
been calculated using the joint design formulae in
ENV 1993-1-1: 1992/A1: 1994

RHS gap joint
All material grade S355J2H
Chord : 200 x 200 x 8
Compression bracing : 150 x 100 x 5 at 90º
Tension bracing : 120 x 80 x 5 at 40º
Joint capacity : Comp brace 402kN
Tens brace 598kN

380kN
590kN

40º
1445kN

1897kN

Compression bracing weld
Using prequalified weld sizes, throat thickness, a = 1.09 t = 5.5mm
Using member load
effective length, s = 2h/sinθ + b = 2 x 100/sin90º + 150 = 350mm
and throat thickness, a = Napp/(pw.s) = 380000 / (250 . 350) = 4.3mm
The required throat thickness is the lesser of these two values, ie 4.3mm

Tension bracing weld
Using prequalified weld sizes, throat thickness, a = 1.09 t = 5.5mm
Using member load
effective length, s = 2h/sinθ + 2b = 2 x 80/sin40º + 2 x 120 = 489mm
and throat thickness, a = Napp/(pw.s) = 590000 / (250 . 489) = 4.8mm
The required throat thickness is the lesser of these two values, ie 4.8mm

SHS welding 27

Design of welds

RHS overlap joint
All material grade S275J2H
Chord : 180 x 180 x 8
Compression bracing : 120 x 120 x 5 at 55º
Tension bracing : 90 x 90 x 5 at 55º
Overlap %, Ov = q sinθ / h = 45 sin55º / 90 = 41%
Joint capacity : Comp brace
Tens brace

280kN

280kN
45

55º

447kN
330kN

Overlapping bracing weld
Using prequalified weld sizes, throat thickness, a = 0.94 t = 4.7mm
Using member load
effective length, s = (Ov/50)2hi + be + be(ov)
10 fyj tj
10 x 8 275 x 8
with be(ov) = —— —— bi = ——— ———— 90 = 64mm < b i = 90mm
bj/tj fyi ti
180 275 x 5

and be =

10 fy0 t0
10 x 5 275 x 5
—— —— bi = ——— ———— 90 = 38mm < bi = 90mm
b0/t0 fyi ti
120 275 x 5

Hence effective length, s = 41 / 50 (2 x 90) + 64 + 38 = 249mm
and throat thickness, a = Napp/(pw.s) = 280000 / (220 . 249) = 5.1mm
The required throat thickness is the lesser of these two values, ie 4.7mm
Overlapped bracing weld
Using prequalified weld sizes, throat thickness, a = 0.94 t = 4.7mm
Using member load effective length,
s = soverlapping (hj+bj)/(hi+bi) = 249 (120+120)/(90+90) = 314mm < 2(hj/sinθj+bj)-bi = 443mm
and throat thickness, a = Napp/(pw.s) = 280000 / (220 . 314) = 4.1mm
The required throat thickness is the lesser of these two values, ie 4.1mm

CHS gap joint
All material grade S355J2H
Chord : 193.7 x 6.3
Compression bracing : 114.3 x 3.6 at 45º
Tension bracing : 88.9 x 3.2 at 45º
Joint capacity : Comp brace
Tens brace

45º
700kN

281kN
281kN

Compression bracing weld
Using prequalified weld sizes, throat thickness, a = 1.09 t = 3.9mm
Using joint capacity method
teff = 0.94 Njoint / d = 0.94 x 281 / 114.3 = 2.32mm > d / 50 = 2.29mm
throat thickness = α teff = 1.09 x 2.32 = 2.6mm
The required throat thickness is the lesser of these two values, ie 2.6mm
Tension bracing weld
Using prequalified weld sizes, throat thickness, a = 1.09 t = 3.5mm
Using joint capacity method
teff = 0.94 Njoint / d = 0.94 x 281 / 88.9 = 2.98mm > d / 50 = 1.78mm
throat thickness = α teff = 1.09 x 2.98 = 3.3mm
The required throat thickness is the lesser of these two values, ie 3.3mm

28 SHS welding

275kN

45º
1090kN

CHS overlap joint
All material grade S275J2H
Chord : 273 x 8.0
Compression bracing : 193.7 x 5.0 at 90º
Tension bracing : 168.3 x 5.0 at 45º
Joint capacity : Comp brace 483kN
Tens brace 683kN

460kN

650kN

45º
1070kN

1530kN

Overlapped bracing weld
Using prequalified weld sizes, throat thickness, a = 0.94 t = 4.7mm
Using joint capacity method
teff = 1.22 Njoint / d = 1.22 x 483 / 193.7 = 3.04mm < d / 50 = 3.87mm
throat thickness = α teff = 0.94 x 3.87 = 3.6mm
The required throat thickness is the lesser of these two values, ie 3.6mm

Overlapping bracing weld
Using prequalified weld sizes, throat thickness, a = 0.94 t = 4.7mm
Using joint capacity method
teff =1.22 Njoint / d = 1.22 x 683 / 168.3 = 4.94mm > d / 50 = 3.37mm
throat thickness = α teff = 0.94 x 4.94 = 4.6mm
The required throat thickness is the lesser of these two values, ie 4.6mm.

Butt welds
The design strength of full penetration butt welds should be taken as
equal to that of the parent metal, provided the weld is made with
electrodes that produce all weld tensile specimens (both yield and tensile)
not less than those specified for the parent metal.

Design note: When designing welds for full width Vierendeel joints, to
cater for the non-uniform stress distribution at the connection and to
ensure that stress re-distribution can take place, the welds should be
designed to have the same capacity as the bracing member capacity.

SHS welding 29

Appendix 1

Table 1
Sizes of RHS and CHS bracings which can be fitted to CHS main members without shaping
Size of bracing (d1) up to and including:-

Diameter of main
member

Straight cut

Partial flattening

(do)

RHS width

CHS dia.

Original dia. of CHS

33.7

42.4

26.9

48.3

26.9

60.3

33.7

76.1

33.7

88.9

26.9

33.7

114.3

33.7

42.4

139.7

33.7

48.3

168.3

33.7

48.3

193.7

42.4

48.3

219.1

42.4

60.3

244.5

42.4

60.3

273.0

42.4

60.3

323.9

48.3

76.1

355.6

48.3

76.1

406.4

48.3

88.9

457.0

60.3

88.9

508.0

60.3

88.9

(All dimensions are in mm)

Note: Partial flattening has been taken as two thirds of the original diameter.

Not to exceed
2mm
Not to
exceed 2mm

30 SHS welding

Table 2A
Length of curve of intersection of CHS bracing on a flat plate or RHS main member
Angle of intersection θ

Size of bracing
d1

30º

35º

40º

45º

50º

55º

60º

65º

70º

80º

90º

26.9

131

118

109

102

33.7

164

148

137

128

122

117

114

111

109

106

42.4

206

186

172

161

153

147

143

139

137

133

48.3

234

212

196

184

175

168

163

159

156

152

60.3

293

264

244

229

218

210

203

198

194

190

189

76.1

369

334

308

290

275

265

256

250

245

239

88.9

432

390

360

338

322

309

299

292

286

280

279

114.3

555

501

463

435

414

398

385

376

368

360

359

139.7

678

613

566

532

506

486

471

459

450

439

168.3

817

738

682

640

609

585

567

553

542

529

193 7

940

850

785

737

701

674

652

636

624

609

219.1

1064

961

888

834

793

762

738

720

706

689

688

244.5

1187

1072

991

930

885

850

824

803

788

769

768

273.0

1325

1198

1106

1039

988

949

920

897

880

859

858

323.9

1572

1421

1312

1232

1172

1126

1091

1064

1044

1019

1018

355.6

1726

1560

1441

1353

1287

1237

1198

1168

1146

1119

1117

406.4

1973

1783

1647

1546

1471

1413

1369

1335

1310

1278

1277

457.0

2218

2005

1852

1739

1654

1589

1539

1501

1473

1437

1436

508.0

2466

2228

2058

1933

1839

1767

1711

1669

1637

1598

1596

(All dimensions are in mm)

d1
Length of curve for 90º bracing = πd and for other angles may be taken as — [ 1 + Cosec + 3
2

1 + Cosec 2 ]

d1
θ

SHS welding 31

Appendix 1

Square sections

Table 2B
Length of intersection of RHS bracing on a flat plate or RHS main member
Angle of intersection θ

Size of bracing
h1 x b1

30º

35º

40º

45º

50º

55º

60º

65º

70º

80º

90º

25 x 25

150

137

128

121

115

111

108

105

103

101

100

30 x 30

180

165

153

145

138

133

129

126

124

121

120

40 x 40

240

219

204

193

184

178

172

168

165

161

160

50 x 50

300

274

256

241

231

222

215

210

206

202

200

60 x 60

360

329

307

290

277

266

259

252

248

242

240

70 x 70

420

384

358

338

323

311

302

294

289

282

280

80 x 80

480

433

409

386

369

355

345

337

330

322

320

90 x 90

540

494

460

435

415

400

388

379

372

363

360

100 x 100

600

549

511

483

461

444

431

421

413

403

400

120 x 120

720

658

613

579

553

533

517

505

495

484

480

140 x 140

840

768

716

676

646

622

603

589

578

564

560

150 x 150

900

823

767

724

692

666

646

631

619

605

600

160 x 160

960

878

818

773

738

711

690

673

661

645

640

180 x 180

1080

988

920

869

830

799

776

757

743

726

720

200 x 200

1200

1097

1022

966

922

888

862

841

826

806

800

250 x 250

1500

1372

1278

1207

1153

1110

1077

1052

1032

1008

1000

300 x 300

1800

1646

1533

1449

1383

1332

1293

1262

1239

1209

1200

350 x 350

2100

1920

1789

1690

1614

1555

1508

1472

1445

1411

1400

400 x 400

2400

2195

2045

1931

1844

1777

1724

1683

1651

1612

1600

(All dimensions are in mm)

Length = 2h1 Cosec θ + 2b
Where h1 = face width of RHS

32 SHS welding

Rectangular sections

Angle of intersection θ

Size of bracing
h1 x b1

30º

35º

40º

45º

50º

55º

60º

65º

70º

80º

90º

50 x 25

250

224

206

191

181

172

165

160

156

152

150

25 x 50

200

187

178

171

165

161

157

155

153

151

150

50 x 30

260

234

216

201

191

182

175

170

166

162

160

30 x 50

220

205

193

185

178

173

169

166

164

161

160

60 x 40

320

289

267

250

237

226

219

212

208

202

200

40 x 60

280

259

244

233

224

218

212

208

205

201

200

80 x 40

400

359

329

306

289

275

265

257

250

242

240

40 x 80

320

299

284

273

264

258

252

248

245

241

240

90 x 50

460

414

380

355

335

320

308

299

292

283

280

50 x 90

380

354

336

321

311

302

295

290

286

282

280

100 x 50

500

449

411

383

361

344

331

321

313

303

300

400

374

356

341

331

322

315

310

306

302

300

50 x 100
100 x 60
60 x 100
120 x 60
60 x120
120 x 80

520

469

431

403

381

364

351

341

333

323

320

440

409

387

370

357

346

339

332

328

322

320

600

538

493

459

433

413

397

385

375

364

360

480

449

427

410

397

386

379

372

368

362

360

640

578

533

499

473

453

437

425

415

404

400

80 x 120

560

519

489

466

449

435

425

417

410

402

400

150 x 100

800

723

667

624

592

566

546

531

519

505

500

100 x 150

700

649

611

583

561

544

531

521

513

503

500

160 x 80

800

718

658

613

578

551

530

513

501

485

480

80 x 160

640

599

569

546

529

515

505

497

490

482

480

200 x 100

1000

897

822

766

722

688

662

641

626

606

600

100 x 200

800

749

711

683

661

644

631

621

613

603

600

250 x 150

1300

1172

1078

1007

953

910

877

852

832

808

800

150 x 250

1100

1023

967

924

892

866

846

831

819

805

800

300 x 200

1600

1446

1333

1249

1183

1132

1093

1062

1039

1009

1000

200 x 300

1400

1297

1222

1166

1122

1088

1062

1041

1026

1006

1000

400 x 200

2000

1795

1645

1531

1444

1377

1324

1283

1251

1212

1200

200 x 400

1600

1497

1422

1366

1322

1288

1262

1241

1226

1206

1200

450 x 250

2300

2069

1900

1773

1675

1599

1539

1493

1458

1414

1400

250 x 450

1900

1772

1678

1607

1553

1510

1477

1452

1432

1408

1400

500 x 300
300 x 500

2600
2200

2343
2046

2156
1933

2014
1849

1905
1783

1821
1732

1755
1693

1703
1 662

1664
1639

1615
1609

1600
1600

(All dimensions are in mm)

SHS welding 33

Appendix 1

Table 2C
Length of curve of intersection of CHS bracing on a CHS main member
Size of
bracing
d1

26.9

33.7

42.4

48.3

60.3

76.1

88.9

114.3

Angle of intersection θ

Size of
main
do

30º

35º

40º

45º

50º

55º

60º

65º

70º

80º

90º

26.9

151

139

131

125

121

118

115

113

112

110

33.7

136

123

115

108

104

100

42.4

133

121

112

105

101

33.7

189

174

164

157

152

148

144

142

140

138

137

42.4

170

155

144

136

130

125

122

119

117

114

48.3

168

152

141

133

127

123

119

116

114

112

111

42.4

237

220

207

198

191

186

182

179

176

174

173

48.3

217

198

185

175

167

162

157

154

151

148

147

60.3

211

192

178

168

160

154

150

146

144

141

140

48.3

270

250

236

225

217

212

207

204

201

198

197

60.3

244

222

206

195

186

179

174

171

168

164

163

76.1

239

217

201

189

181

174

169

165

162

158

157

60.3

338

312

294

281

271

264

259

254

251

247

246

76.1

304

276

257

243

232

224

217

212

209

204

203

88.9

300

272

252

238

227

218

212

207

204

199

198

114.3

297

269

249

234

223

214

208

203

199

195

193

76.1

426

394

371

355

343

333

326

321

317

312

310

88.9

388

354

329

311

298

288

280

274

270

264

262

114.3

378

343

318

300

286

275

267

261

256

251

249

139.7

375

339

314

296

282

271

263

257

252

246

244

88.9

498

460

434

415

400

389

381

375

370

364

363

114.3

447

407

378

356

341

328

319

312

307

300

298

139 7

440

399

370

349

332

320

311

303

298

291

289

114.3

640

592

558

533

515

501

490

482

476

468

466

139.7

579

527

490

463

442

427

415

406

399

391

388

168.3

568

516

478

451

430

414

402

393

386

377

375

193.7
219.1

564
562

511
509

474
471

446
443

425
422

409
406

397
394

388
385

381
377

372
364

369
366

(All dimensions are in mm)

Length of curve may be taken as a+b+3 a2+b2
d1
Where:- a = — Cosec θ
2

φ = 2 Sin-1 (d1/do)
d1

do φ
b = — - Where φ is measured
4
in radians (1 radian = 57.296º)

2a
d0
θ

34 SHS welding

Size of
bracing
d1

139.7

168.3

193 7

219.1

244.5

273.0

323.9

355.6

406.4

457.0
508.0

Angle of intersection θ

Size of
main
do

30º

35º

40º

45º

50º

55º

60º

65º

70º

80º

90º

139.7

782

723

682

651

629

612

599

589

582

573

570

168.3

709

645

600

567

542

523

509

498

490

479

476

193.7

698

634

588

554

529

510

495

484

476

465

462

219.1

692

628

582

548

523

503

488

477

468

458

455

244 5

689

624

578

544

518

499

484

473

464

454

450

168.3

942

871

821

785

758

737

722

710

701

690

686

193.7

861

785

731

691

661

639

622

609

599

587

583

219.1

845

769

714

674

643

620

603

589

579

567

563

244.5

838

760

705

665

634

611

593

580

569

557

553

273.0

832

755

699

659

628

604

587

573

563

550

546

193.7

1085

1003

945

903

872

848

830

817

806

794

790

219.1

994

907

845

800

766

740

720

705

694

680

676

244.5

976

888

825

779

745

718

698

683

671

657

652

273.0

966

877

814

767

732

706

685

664

658

643

639

323.9

957

867

803

756

721

694

673

658

646

631

627

219.1

1227

1134

1069

1022

986

960

939

924

912

898

894

244.5

1128

1030

960

909

870

841

819

802

789

774

769

273.0

1106

1006

936

883

844

814

792

774

761

745

740

323.9

1089

988

917

864

824

794

771

753

739

723

718

355.6

1084

983

910

857

817

787

764

746

732

716

711

244.5

1369

1266

1193

1140

1101

1071

1048

1031

1018

1002

997

273.0

1259

1149

1071

1014

971

939

914

895

881

863

858

323.9

1226

1114

1035

976

932

899

873

853

839

821

815

355.6

1217

1104

1024

965

921

887

861

842

827

809

803

406.4

1208

1095

1014

955

910

876

850

830

815

797

791

273.0

1529

1414

1332

1273

1229

1196

1170

1151

1137

1119

1113

323.9

1388

1265

1177

1112

1064

1027

999

977

961

941

935

355.6

1371

1247

1158

1093

1044

1006

978

956

940

919

813

406.4

1357

1231

1141

1075

1026

988

959

937

921

900

894

323.9

1814

1677

1580

1510

1458

1419

1389

1366

1349

1328

1321

355.6

1675

1530

1427

1352

1296

1253

1220

1195

1176

1153

1146

406.4

1634

1486

1381

1304

1246

1202

1169

1143

1124

1100

1092

457.0

1616

1467

1361

1283

1224

1180

1146

11 20

1100

1076

1068

508.0

1605

1455

1349

1270

1212

1167

1132

1106

1086

1062

1054

355.6

1991

1841

1735

1658

1601

1557

1524

1499

1481

1458

1450

406.4

1821

1661

1547

1463

1401

1353

1317

1289

1268

1243

1235

457.0

1789

1627

1511

1426

1362

1314

1277

1248

1227

1201

1193

508.0

1772

1609

1492

1407

1342

1293

1256

1227

1206

1179

1171

406.4

2276

2104

1983

1895

1830

1780

1742

1714

1692

1666

1658

457.0

2089

1906

1776

1681

1610

1556

1514

1483

1459

1430

1421

508.0

2051

1866

1734

1638

1565

1510

1468

1435

1411

1381

1372

457.0

2559

2366

2230

2131

2057

2002

1959

1927

1903

1873

1864

508.0

2356

2151

2005

1898

1818

1758

1711

1626

1649

1617

1607

508.0

2845

2630

2479

2369

2287

2225

2178

2142

2115

2082

2072

(All dimensions are in mm)

SHS welding 35

Appendix 2

Stage 2

Stage 1

o.d. of branch
1 4

Divide / circle into 3

nch

f bra

i.d o

Divide half
circle into 6
Angle of
branch
7
6

1
5
4

emb

in m

ma
. of

o.d

L6
L5

L3
L4

Templates for profile shaping ends of CHS bracing
to fit CHS main member
The usual procedure for making templates for marking-off for
profile-shaping the ends of CHS is as follows:
1. Draw a vertical line with a horizontal line cutting it. Above the
horizontal line draw a circle equal in diameter to the INTERNAL
DIAMETER of the branch (bracing) and divide the quarter circle
into three equal parts. Below the horizontal line draw an arc
equal in diameter to the OUTSIDE DIAMETER of the main
member. Project the divisions from the quarter-circle on to the
arc and draw horizontal lines from the points where these
intersect.
2. Draw a separate circle equal in diameter to the OUTSIDE
DIAMETER of the branch, and from its centre draw a line to cut
the horizontal lines at the angle required between the branch
and the main member. Divide half of this circle into 6 equal
parts and join these to the horizontal lines from stage 1,
numbering the points of intersection 1 to 7.

36 SHS welding

L2
L1

L3
L1

Required
profile
Length = circumference of branch

12 equal parts
1

3. Now on a card or paper template draw a straight line equal
in length to the circumference of the branch and divide it into
12 equal parts numbered as shown. Mark off the length L1 to
L6 from stage 2 on the template as shown and join up their
extremities with a fair curve. This gives the shape of the profile
to which the end of the branch should be cut. The profile
template may then be cut out and wrapped around the end of
the branch tube for marking-off purposes.

SHS welding 37

Reference standards & documents

Structural steel hollow sections & materials:
EN 10210-1 EN 10210-2 EN 10219-1 EN 10219-2 BS 7668 TS30 -

Hot finished structural hollow sections of non-alloy and fine grain structural
steels- Part 1: Technical delivery requirements.
Hot finished structural hollow sections of non-alloy and fine grain structural
steels- Part 2: Tolerances, dimensions and sectional properties.
Cold formed welded structural hollow sections of non-alloy and fine grain
steels- Part 1: Technical delivery requirements.
Cold formed welded structural hollow sections of non-alloy and fine grain
steels- Part 2: Tolerances, dimensions and sectional properties.
Weldable structural steels: Hot finished structural hollow sections in weather
resistant steels.
Corus Tubes specification for Strongbox® 235

Welding:
EN 439 EN 440 EN 499 EN 758 EN 1011-1 EN 1011-2 EN 29692 -

Welding Consumables. Shielding gases for arc welding and cutting.
Welding Consumables. Wire electrodes and deposits for gas shielded metal
arc welding of non-alloy and fine grain steels. Classification.
Welding Consumables. Covered electrodes for manual metal arc welding of
non-alloy and fine grain steels. Classification.
Welding Consumables. Tubular cored electrodes for metal arc welding with
or without a gas shield of non-alloy and fine grain steels. Classification.
Welding - Recommendations for welding of metallic materials Part 1: General guidance for arc welding.
Welding - Recommendations for welding of metallic materials Part 2 : Ferritic steels.
Metal-arc welding with covered electrode, gas-shielded.
Metal-arc welding and gas welding - Joint preparations for steel.

13920-2 -

Testing & inspection:
EN 287-1 EN 288-1 -

Approval testing of welders for fusion welding - Part 1 : Steels.
Specification and approval of welding procedure for metallic materials Part 1 : General rules for fusion welding.
EN 288-3 Specification and approval of welding procedure for metallic materials Part 3 : Welding procedure tests for the arc welding of steels.
EN 288-8 Specification and approval of welding procedure for metallic materials Part 8 : Approval by a pre-production welding test.
EN 970 Non-destructive examination of welds - Visual examination.
EN 1290 Non-destructive examination of welds - Magnetic particle examination
of welds.
EN 1714 Non-destructive examination of welds - Ultrasonic examination of welded
joints.
EN 12062 Non-destructive examination of welds - General rules, for metallic materials.
BS 4872: Part 1 - Approval testing of welders when welding procedure approval is not required
Part 1 - Fusion welding of steel.

38 SHS Welding

Application standard:

BS 5400 BS 5950-1: 2000 ENV 1993 :
ENV 1994 :
ENV 1090-1 ENV 1090-4 -

Steel, concrete and composite bridges.
Structural use of steelwork in building Part 1 - Code of practice for design
-Rolled and welded sections.
Eurocode 3: Design of steel structures.
Eurocode 4: Design of composite steel and concrete structures.
Execution of Steel Structures - Part 1 : General Rules and Rules for
Buildings.
Execution of Steel Structures - Part 4 : Supplementary Rules for Hollow
Section Structures.
Note: EN's and ENV's are published in the UK by The British Standards Institute as BS EN's and
BS DD ENV's respectively ‘pr’ designates a draft standard

General
'Health and Safety in Welding and Allied Processes' and 'Safe Working with Arc Welding'
obtainable from:
The Welding Institute,Abington Hall, Abington, Cambridge, CB1 6AL.
Tel: O1223 891162
Fax: 01223 892588
E-mail: twi@twi.co.uk
'National Structural Steelwork Specification for Building Construction'
obtainable from:
British Constructional Steelwork Association Ltd ,4, Whitehall Court, Westminster, London, SW1A 2ES.
Tel: 020 7839 8566
Fax: 020 7976 1634
E-mail: postroom@steelconstruction.org

*CIDECT design guides
No.1 -

'Design Guide for Circular Hollow Section (CHS) Joints under Predominantly
Static Loading', Verlag TUV Rheinland, Cologne, Germany, 1991,
ISBN 3-88585-975-0.

No.3-

'Design Guide for Rectangular Hollow Section (RHS) Joints under
Predominantly Static Loading', Verlag TUV Rheinland, Cologne, Germany, 1992,
ISBN 3-8249-0089-0.

No.6 -

'Design Guide for Structural Hollow Sections in Mechanical Applications',
Verlag TUV Rheinland, Cologne, Germany, 1995, ISBN 3-8249-0302-4.

No.7 -

'Design Guide for Structural Hollow Sections - Fabrication, Assembly and Erection',
Verlag TUV Rheinland, Cologne, Germany, 1998, ISBN 3-8249-0443-8.

*CIDECT Design Guides obtainable from:
The Steel Construction Institute, Silwood Park, Ascot, Berkshire, SL5 7QN.
Tel: 01344 623345
Fax: 01344 622944
E-mail: publications@steel-sci.com

SHS Welding 39

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CT15:1000:UK:04/2005

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CT15 SHS Welding Structural Hollow Sections

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