Design Welded Joints

Design of welded joints

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Design of welded CHS and RHS-joints

NS-EN 1993-1-8

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EC3 Part 1-8: Table of contents

1. Introduction

2. Basis of design

3. Connections made with bolts, rivets or pins

4. Welded connections

5. ��Analysis, classification and modelling

6. Structural joints connecting H or I sections

7. Hollow section joints


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5.1.5 Global analysis of lattice girder

(2) The distribution of axial forces in a lattice girder may be determined

on the assumption that the members are connected by

pinned joints.

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(3) Secondary moments at the joints, caused by the rotational stiffnesses

of the joints, may be neglected both in the design of the

members and in the design of the joints, provided that both of

the following conditions are satisfied:

• the joint geometry is within the range of validity specified in

Table 7.1, Table 7.8, Table 7.9 or Table 7.20 as appropriate;

• the ratio of the system length to the depth of the member in the

plane of the lattice girder is not less than the appropriate minimum

value.

• For building structures, the appropriate minimum value may be

assumed to be 6.


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(4) The moments resulting from transverse loads

that are applied between panel points,

should be taken into account in the design

of the members to which they are applied.

Provided that the conditions given in

5.1.5(3) are satisfied:

• the brace members may be considered as

pin-connected to the chords, so moments

resulting from transverse loads applied to chord

members need not be distributed into brace

members, and vice versa;

• the chords may be considered as continuous

beams, with simple supports at panel points.

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7.2 Design

7.2.1 General

(1)P The design values of the internal axial forces both in the brace

members and in the chords at the ultimate limit state shall not

exceed the design resistances of the members determined from

EN 1993-1-1.

(2)P The design values of the internal axial forces in the brace

members at the ultimate limit state shall also not exceed the

design resistances of the joints given in 7.4, 7.5, 7.6 or 7.7 as

appropriate.


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7.2 Design

(3) The stresses σ0,Ed or σp,Ed in the chord at a joint should be

determined from:

∑>

−=

+=

+=

0,,0,

0,

,0

0

,

,

0,

,0

0

,0

,0

cos

where

...(7.2)

...(7.1)

iiEdiEdEdp

el

EdEdp

Edp

el

EdEd

Ed

NNN

W

M

A

N

W

M

A

N

θ

σ

σ

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(5) Moments resulting from eccentricities may be neglected in the design

of tension chord members and brace members. They may also

be neglected in the design of connections if the eccentricities are

within the following limits:

-0,55 d0 ≤ e ≤ +0,25 d0

-0,55 h0 ≤ e ≤ +0,25 h0

5.1.5 Global analysis of lattice girders


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Table 5.3 Allowance for bending moments

Type of component Source of the bending moment

Secondary effects Transverse loading Eccentricity

Compression chord

No if 5.1.5(3)

is satisfied

Yes

Yes

Tension chord No

Brace member No

Joint No

if 5.1.5(5) is

satisfied

CIDECTPane frame joint modelling assumptions to obtain realistic forces for member design

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EC3 Part 1-8: Table of contents

1. Introduction

2. Basis of design

3. Connections made with bolts, rivets or pins

4. Welded connections

5. Analysis, classification and modelling

6. Structural joints connecting H or I sections

7. �� Hollow section joints

7.3 Welds

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7.3.1 Design resistance(1)P The welds connecting the brace members to the chords shall be

designed to have:

• sufficient resistance to allow for non-uniform stress-distributions

• sufficient deformation capacity to allow for redistribution of bending

moments.

(2) In welded joints, the connection should normally be formed around the

entire perimeter of the hollow section by means of a butt weld, a

fillet weld, or combinations of the two. …

(3) …

(4) The design resistance of the weld, per unit length of perimeter of a brace

member, should not normally be less than the design resistance of

the cross-section of that member per unit length of perimeter.

�� Full-strength welds are required!


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NS-EN 1090-2: Annex E

Welded joints in hollow sections

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Figure E.5 — Weld preparation and fit-upFillet welds in square or rectangular hollow section brace to chord joints

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Welded RHS connections– T-joints

– Y-joints

– X-joints

– K-joints(with gap and overlap)

Combined joints– N-joint

(with gap and overlap)

– KT-joint(with gap and overlap)

Figure 7.1: Types of joints in RHS lattice girders


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Joint parameters

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If the gap equals e.g. 50 mm, then …

Table 7.8: Note 1)

If g/b0 > 1,5(1-β) and g ≥ t1 + t2

treat the joint as two separate T or Y joints.


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Gap joints

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RHS 200x12

RHS 250x250x12

RHS 200x12

200 200

50

have the following advantages:

• easy fabrication,

• easy welding,

• easy NDT,

• easy surface treatment

have some disadvantages:

• increased engineering costs

• increased steel sections

• may be prone to fatigue

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Figure 7.3: Failure modes for joints of RHS members

Various failure modes for a K-joint of rectangular hollow sections:

a. Chord face failure

b. Chord wall side failure

c. Chord shear failure

d. Punching shear

e. Brace failure (effective width)

f. Local buckling of brace

If the welds are not strong enough, weld failure can also occur or if the

material does not have sufficient through thickness properties

lamellar tearing is possible.


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Welded hollow section joints

Sub chapter 7.4 7.5 7.6 7.7

Braces CHS CHS or RHS CHS or RHS CHS or RHS

Chords CHS RHS I or H sections U sections

Range of validity

Table 7.1 Tables

7.8 & 7.9

Table 7.20 Table 7.23

Uniplanar

welded joints

Table 7.2 Tables

7.10 - 7.12


Multiplanar

welded joints

Table 7.7 Table 7.19 - -

Special types

of welded joints


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Basis of section classification

Rectangular (RHS) and circular (CHS) hollow section.

dt

h

b

Flange

Web t

c = b - 3t

or

c = h - 3t


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Table 5.2 (Extract): Maximum width-to-thickness ratios

for compression parts c/t or d/t

Class RHS

Bending

RHS

Compression

CHS

1 c/t ≤ 72ε c/t ≤ 33ε d/t ≤ 50ε2

2 c/t ≤ 83ε c/t ≤ 38ε d/t ≤ 70ε2

3 c/t ≤ 124ε c/t ≤ 42ε d/t ≤ 90ε2

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EC3-1-8 Required cross-section class

RHS 1 CHS

Table 7.3 Table 7.1

Class 2 1, 2

&

b/t ≤ 35 and h/t ≤ 35

Class 2

&

10 ≤ d/t ≤ 50

Note

1. Class 1 for joint type K-overlap, N-

overlap and CHS brace member

2. The compression elements of the

members should satisfy the

requirements for Class 1 or Class

2 given in EN 1993-1-1 for the

condition of pure bending.


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7 Hollow section joints

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7.1 General

7.2 Design

7.2.1 General

7.2.2 Failure modes for hollow section joints

7.3 Welds

7.4 �� Welded joints between CHS members 7.4.1 General

7.4.2 Uniplanar joints7.4.3 Multiplanar joints

7.5 Welded joints between CHS or RHS braces and RHS chords

7.5.1 General

7.5.2 Uniplanar joints

7.5.3 Multiplanar joints

7.6 Welded joints between CHS or RHS braces and I or H chords

7.7 Welded joints between CHS or RHS braces and U chords

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Table 7.2Design axial resistances of T, Y & X joints (CHS)


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Table 7.2Design axial resistances of K joints (CHS)

The reduction factor kg

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7 Hollow section joints

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7.1 General

7.2 Design

7.2.1 General

7.2.2 Failure modes for hollow section joints

7.3 Welds

7.4 Welded joints between CHS members

7.4.1 General



7.5 �� Welded joints between CHS or RHS braces and RHS chords7.5.1 General

7.5.2 �� Uniplanar joints


7.6 Welded joints between CHS or RHS braces and I or H chords

7.7 Welded joints between CHS or RHS braces and U chords


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7.5.2.1 Unreinforced joints(1) …

(2) …

(3) For joints within the range of validity of Table 7.9, the only design

criteria that need be considered are chord face failure and brace failure

with reduced effective width. The design axial resistance should betaken

as the minimum value for these two criteria.

NOTE:The design axial resistances for joints of hollow section brace members to square hollow section chords given in Table 7.10 have been simplified by omitting design criteria that are never critical within the range of validity of Table 7.9.


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Table 7.9:

Additional condition for the use of Table 7.10

Note: Square hollow sections!

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Table 7.10: (square RHS)Design axial resistances of T, Y & X joints (β ≤ 0,85)


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Table 7.10: (square RHS)Design axial resistances of K joints

The reduction factor kp

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0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 0,2 0,4 0,6 0,8 1


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The reduction factor kn

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0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 0,2 0,4 0,6 0,8 1

β = 0,85

β = 0,75

β = 0,65

β = 0,55

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Table 7.11Design axial resistances of T, Y & X joints


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Design axial resistances of welded T, X and Y joints

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Table 7.12Design axial resistances of K joints (RHS)


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Joints subjected to combined bending and axial force

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Table 7.15: Design resistances moments of welded joints (CHS)


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Table 7.14: Design resistances moments of welded joints (RHS)

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Table 7.14: Design resistances moments of welded joints (RHS)

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Design Welded Joints

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