Design of SHS Welded Joints.pdf

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TUB 2765 SHS Welded Joints
Corus Tubes
Design of SHS welded joints
Structural & Conveyance Business
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Design of SHS
Contents
1
Introduction
02
1.1 Product specification
03
2
Scope
04
2.1 Joint geometry
04
2.2 Material
06
2.3 Multiplanar joints
06
2.4 Load and moment interaction
07
3
General design guidance
08
3.1 Structural analysis
08
3.2 Welding
09
3.3 Fabrication
11
4 Parameters affecting joint capacity 13
4.1 General
13
4.2 Joint failure modes
13
4.3 Joints with a single bracing
15
4.4 Joints with a gap between bracings
16
4.5 Joints with cverlapped bracings
16
4.6 Joint reinforcement
17
5
Joint design formulae
20
5.1 CHS chord joints
20
5.2 RHS chord joints
25
5.3 Special joints in RHS
30
5.4 I - or H- section chord joints
32
6
Design examples
35
6.1 Girder layout and member loads
35
6.2 Design philosophy
36
6.3 RHS girder design
36
6.4 CHS girder design
39
7
List of symbols
43
7.1 General alphabetic list
43
7.2 Pictorial list
44
8
References
45
01 Design of SHS welded joints
welded joints
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1. Introduction
In construction with structural hollow sections the members are generally
welded directly to each other and, as a result, member sizing has a direct
effect on both the joint capacity and the cost of fabrication. In order to obtain
a technically secure, economic and architecturally pleasing structure, both
the architect and design engineer must, from the very beginning, be aware of
the effects that their design decisions will have on the joint capacity, the
fabrication, assembly and the erection of the structure.
Structural hollow sections have a higher strength to weight ratio than open
section profiles such as I-, H- and L- sections. They also require a much
smaller weight of protection material, whether this is a fire protection or
corrosion coating, because of their lower external area.
A properly designed steel construction using structural hollow sections will
nearly always be lighter in terms of material weight than a similar construction
made with open section profiles and, although structural hollow sections are
more expensive than open section profiles on a per tonne basis, the overall
weight saving of steel and protective coatings will very often result in a much
more cost effective construction.
This publication has been produced to show how the joint capacity of
staticaly loaded joints can be calculated and how it can be affected by both
the geometric layout and the sizing of the members.
Considerable international research into the behaviour of structural hollow
section (SHS) welded joints for lattice type constructions has enabled
comprehensive design recommendations to be developed which embrace
the large majority of manufactured structural hollow sections.
These design recommendations have been developed by CIDECT (Comité
International pour la Développement et l'Étude de la Construction Tubulaire)
and the IIW (International Institute of Welding) and, as a result, have gained
considerable international recognition and acceptance. They have been used
in a series of CIDECT Design Guides [1,2] and are now incorporated into
Eurocode 3 : Annex K.[3]
The joint capacity formulae, reproduced in section 5, were developed and are
presented in a limit states form and are therefore fully compatible with the
requirements of BS 5950 : Part 1 [4] and Eurocode 3.
A software program [5], called CIDJOINT, has been developed by CIDECT for
the design of most of the joints described in this design publication. The
CIDJOINT design program requires MS-Windows version 3.x (or higher).
The design recomendations can be used with Corus Tubes Celsius ® hot
finished hollow sections to EN 10219 [6, 7], cold formed Hybox ® 355 hollow
sections to EN 10219 [8, 9] and cold formed Strongbox ® 235 hollow sections
to Corus Tubes specification TS30 [10]
Design of SHS welded joints 02
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1.1 Production 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
Cold formed hollow sections
Hot finished hollow sections
Strongbox ® 235 Hybox ® 355
Celsius ® 275
Celsius ® 355
Specification
TS 30 (1)
EN 10219 355J2H EN 10210 275J2H EN 10210 355J2H
C % max
0.17
0.22
0.20
0.22
Si % max
-
0.55
-
0.55
Mn % max
1.40
1.60
1.50
1.60
P % max
0.045
0.035
0.035
0.035
S % max
0.045
0.035
0.035
0.035
Ni % max
0.009
-
-
-
CEV % t
16mm
0.35
0.45
0.41
0.45
(1)
Corus Tubes specification TS 30, generally in accordance with EN 10219 235JRH.
Mechanical properties
Cold formed hollow sections
Hot finished hollow sections
Strongbox ® 235
Hybox ® 355
Celsius ® 275
Celsius ® 355
Specification
TS 30 (1)
EN 10219 355J2H EN 10210 275J2H
EN 10210 355J2H
Tensile strength R m N/mm 2
t < 3mm
340 min
510-680
430-580
510-680
3 < t
40mm
490-630
410-560
490-630
Yeild strength R eh min N/mm 2
t
16mm
235
355
275
355
t > 16mm
-
-
-
345
Min Elongation %
L o =5.65
S 0 t
40mm
24 (2)(3)
20 (2)(3)
22
22
Impact properties
Min Ave energy (J)
-
27 @ -20ºC
27 @ -20ºC
27 @ -20ºC
10 x 10 specimen
(1)
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 0.9t nom or (t nom -0.5mm) whichever is the larger.
03 Design of SHS welded joints
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2 Scope
This publication has been written mainly for plane frame girder joints under predominantly static axial
and/or moment loading conditions, however, some advice on non-planar frame joints is also given.
Note: In calculations this publication uses the convention that tensile forces and stresses are positive
(+) and compressive ones are negative (-).
2.1 Joint geometry
The main types of joint configuration covered in this publication are shown in figure 1, however, other
types of connections to structural hollow section main members, such as fin plates and cross plates,
are also discussed.
X-joints
T-and Y-joints
K-and N-joints with gap
K-and N-joints with overlap
Figure 1 : Joint geometries
The angle between the chord and a bracing or between two bracings should be between 30º and 90º
inclusive. If the angle is less than 30º then :
1. the designer must ensure that a structurally adequate weld can be made in the acute angle.
and 2. any joint capacity calculation should be made using an angle of 30º instead of the actual angle.
When K- or N-joints with overlapping bracings are being used, the overlap must be made with the first
bracing running through to the chord and the second bracing either sitting on both the chord and the
first bracing (partial overlap) or sitting fully on the first bracing (fully overlapped) as shown in (figure 2a).
The joint should never be made by cutting the toes from each bracing and butting them up together
(figure 2b), because this is both more difficult to fit together satisfactorily and, more importantly, can
result in joint capacities up to 20% lower than those calculated by the joint design formulae given in
section 5. A modified version of the type of joint shown in (figure 2b) can, however, be used provided
that a plate of sufficient thickness is inserted between the two bracings - see section 4.6.3 on RHS
chord overlap joint reinforcement.
Design of SHS welded joints 04
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