ISO 14347:2008

INTERNATIONAL ISO
STANDARD 14347
First edition
2008-12-01
Fatigue — Design procedure for welded
hollow-section joints —
Recommendations
Fatigue — Procédure de dimensionnement à la fatigue des
assemblages soudés de profils creux — Recommandations

Reference number
©
ISO 2008
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©  ISO 2008
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ii © ISO 2008 – All rights reserved

Contents Page
Foreword .iv
1 Scope.1
1.1 General .1
1.2 Materials .1
1.3 Types of joints .1
2 Normative references.1
3 Terms and definitions .2
4 Symbols and abbreviated terms .7
5 Cumulative fatigue damage.12
6 Partial safety factor .12
7 Fatigue design procedures.12
7.1 Hot-spot stress method .12
7.2 Design procedures .13
8 Fatigue strength .13
8.1 Member forces .13
8.2 Nominal stress ranges.14
8.3 SCF calculations.14
8.4 Hot-spot stress ranges .14
8.5 Fatigue strength curves.15
9 SCF calculations for CHS joints .17
9.1 Uniplanar CHS T- and Y-joints .17
9.2 Uniplanar CHS X-joints .18
9.3 Uniplanar CHS K-joints with gap .18
9.4 Multiplanar CHS XX-joints .19
9.5 Multiplanar CHS KK-joints with gap.20
9.6 Minimum SCF values .21
10 SCF calculations for RHS joints .21
10.1 Uniplanar RHS T- and X-joints .21
10.2 Uniplanar RHS K-joints with gap .22
10.3 Uniplanar RHS K-joints with overlap.23
10.4 Multiplanar RHS KK-joints with gap.24
10.5 Minimum SCF values .25
Annex A (normative) Quality requirements for hollow sections.26
Annex B (normative) Weld details.27
Annex C (informative) A fatigue assessment procedure .29
Annex D (normative) SCF equations and graphs for CHS joints.31
Annex E (normative) SCF equations and graphs for RHS joints .47
Bibliography.67

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
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International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 14347 was prepared by the International Institute of Welding, Commission XV, Design, analysis and
fabrication of welded structures, recognized as an international standardizing body in the field of welding in
accordance with Council Resolution 42/1999.
Requests for official interpretations of any aspect of this International Standard should be directed to the ISO
Central Secretariat, who will forward them to the IIW Secretariat for an official response.

iv © ISO 2008 – All rights reserved

INTERNATIONAL STANDARD ISO 14347:2008(E)

Fatigue — Design procedure for welded hollow-section joints —
Recommendations
1 Scope
1.1 General
This International Standard gives recommendations for the design and analysis of unstiffened, welded, nodal
joints in braced structures composed of hollow sections of circular or square shape (with or without
rectangular chord) under fatigue loading.
This International Standard applies to structures:
a) fulfilling quality requirements for hollow sections (see Annex A);
b) complying with recommended weld details (see Annex B);
c) employing permitted steel grades (see 1.2);
d) having hollow section joints (see 1.3);
e) having either
1) square or rectangular hollow sections with a thickness between 4 mm and 16 mm, or
2) circular hollow sections with a thickness between 4 mm and 50 mm;
f) having as stress range the range of “hot-spot” stress;
g) having identical brace (branch) members.
1.2 Materials
This International Standard applies to both hot-finished and cold-formed steel structural hollow sections,
complying with the applicable national manufacturing specification, that fulfil specified quality requirements
(see Annex A).
1.3 Types of joints
This International Standard applies to joints consisting of circular hollow sections (CHS) or rectangular hollow
sections (RHS) as used in uniplanar or multiplanar trusses or girders, such as T-, Y-, X-, K-, XX-, and
KK-joints (see Figure 1 and Figure 2).
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 630:1995, Structural steels — Plates, wide flats, bars, sections and profiles
a)  CHS T-joints b)  CHS Y-joints c)  CHS X-joints d)  CHS K-joints
with gap
e)  RHS T-joints f)  RHS X-joints g)  RHS K-joints h)  RHS K-joints
with gap with overlap
NOTE RHS are assumed to be square, although this International Standard is likely to be applicable to rectangular
chord members, welded to square branch members.
Figure 1 — Types of uniplanar joints covered by this International Standard

a)  CHS XX-joints b)  CHS KK-joints with gap c)  RHS KK-joints with gap
NOTE RHS are assumed to be square, although this International Standard is likely to be applicable to rectangular
chord members, welded to square branch members.
Figure 2 — Types of multiplanar joints covered by this International Standard
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
brace
branch
〈welded hollow section joints〉 cut and welded member
See Figure 3.
2 © ISO 2008 – All rights reserved

Key
1 load applied in the branch
2 crown point
3 branch
4 saddle point
5 weld
6 chord
a)  Joint nomenclature
Key
1 chord wall
2 stress increase due to weld geometry
3 brace hot-spot stress
4 weld toe
5 extrapolation of geometric stress distribution to weld toe
6 stress in branch
7 nominal stress
8 increase in stress due to overall joint geometry
9 branch wall
10 weld
b)  Stress distribution in branch
Figure 3 — Hot-spot stress definition in nodal joints
Key
1 chord wall
2 stress increase due to weld geometry
3 chord hot-spot stress
4 weld toe
5 extrapolation of geometric stress distribution to weld toe
6 stress in chord
7 nominal stress
8 increase in stress due to overall joint geometry
9 branch wall
c)  Stress distribution in chord
Figure 3 (continued)
3.2
constant amplitude fatigue limit
〈welded hollow section joints〉 stress range for a specific ∆S-N curve when the number of cycles, N, is 5 million
or greater
3.3
cut-off limit
stress range for a specific ∆S-N curve when the number of cycles, N, is 100 million or greater, used in the
assessment of fatigue under variable amplitude loading
3.4
fatigue
deterioration of a component due to the initiation and growth of cracks under fluctuating loads
3.5
fatigue life
endurance
N
f
number of applied cycles to achieve a defined failure criterion
[ISO 1099:2006, 3.14]
NOTE In this International Standard, crack growth through the wall thickness is considered as failure.
3.6
gap length
g
distance measured along the length of the connecting face of the chord between the toes of the adjacent
brace members
See Figure 4.
4 © ISO 2008 – All rights reserved

Key
1 member (overlapping in the lower diagram)
2 optionally overlapped member
NOTE For variable definitions, see Clause 4.
Figure 4 — Definition of gap g and overlap q
3.7
hot-spot stress
〈welded hollow section joints〉 point along the weld vicinity where the extrapolated primary stress has its
maximum value (i.e. the maximum geometric stress)
NOTE This definition differs from the more general definition of hot-spot stress as the structural stress at the weld toe.
The extrapolation is carried out from the region outside the influence of the effect on the stress of geometric discontinuities
due to the joint configuration, but close enough to fall inside the zone of the stress gradient caused by the global
geometrical effects of the connection. The extrapolation is carried out on the branch or brace (cut and welded member)
side and the chord (continuous member) side of each weld (see Figure 3). The hot-spot stress can be determined by
considering the stress perpendicular to the weld toe for the chord and the stress parallel to the brace axis for the brace.
3.8
nominal stress
〈welded hollow section joints〉 maximum stress in a cross-section calculated on the actual cross-section by
simple elastic theory without taking into account the effect of geometrical discontinuities due to the joint
configuration on the stress
3.9
overlap
O
v
ratio of the overlap length, q, to the projected connecting length to chord of overlapping brace, p
NOTE The overlap is expressed as a percentage.
See Figure 4, where b = h = h , t = t , and θ = θ . See Clause 4 for the variable definitions.
1 1 2 1 2 1 2
3.10
∆S-N curve
curve giving the relation between the stress range and the number of cycles to failure
NOTE 1 Conventionally, the range of stress is plotted on the vertical axis and the number of cycles on the horizontal
axis using logarithmic scales for both axes.
NOTE 2 The ∆S-N curves given in this International Standard have been derived from a statistical analysis of relevant
experimental data and represent lives that are less than the mean life by two standard deviations of lg N.
3.11
stress concentration factor
SCF
K
t
〈welded hollow section joints〉 ratio between the hot-spot stress at the joint and the nominal stress in the
member due to a basic member load that causes this hot-spot stress
NOTE In joints with more than one branch, each branch is considered. Generally, stress concentration factors are
calculated for the chord and branch.
3.12
stress range
∆S
arithmetic difference between the maximum and minimum stress
∆S = S − S
max min
NOTE 1 Adapted from ISO 1099:2006, 3.10.
NOTE 2 The nominal stress range is based on the nominal stresses while the hot-spot stress range is based on hot-
spot stresses.
See Figure 5.
Key
S tensile stress
−S compressive stress
Figure 5 — Stress range, ∆S, and stress ratio, R
6 © ISO 2008 – All rights reserved

3.13
stress ratio
R
algebraic ratio of the minimum and maximum stress of a cycle:
R = S /S
min max
[ISO 11782-1:1998, 3.6]
NOTE Tension is taken as positive and compression as negative.
See Figure 5.
3.14
structural stress
geometric stress
〈welded hollow section joints〉 linearly distributed stress across the section thickness that arises from applied
loads and the corresponding reaction of the particular structural part, taking account of all geometrical
discontinuities but excluding the notch effects of local structural discontinuities (e.g. weld toe)
4 Symbols and abbreviated terms
A cross-sectional area of a member
a throat thickness
b RHS chord width
b width of brace i
i
C chord-end fixity factor
D cumulative fatigue damage index
d CHS chord diameter
d diameter of brace i (CHS)
i
e joint eccentricity
F axial force
ax
F force in chord
ch
F force in carry-over brace
cov
F function in determining SCF (see D.1.2, D.2.2)
i
F force of reference brace
ref
f correction factor
c
f magnification factor
m
f multiplanar correction factor (see Tables 4 and 5)
mc
g gap length
g′ ratio of the gap length to the chord wall thickness, g/t
h RHS chord depth
h depth of brace i
i
K stress concentration factor
t
K reference SCF for brace under basic balanced axial loading
t,0,b,ax
K carry-over SCF for brace at location 4 (see D.4.2.1.2.2)
t,0,b ,cov
K reference SCF for brace at location 4 (see D.4.2.1.1.2)
t,0,b ,ref
K reference SCF for chord under basic balanced axial loading
t,0,ch,ax
K carry-over SCF for chord at location 2 (see D.4.2.1.2.1)
t,0,ch ,cov
K reference SCF for chord at location 2 (see D.4.2.1.1.1)
t,0,ch ,ref
K SCF for load condition “axial force in brace”
t,ax,b
K SCF for load condition “axial force in chord”
t,ax,c
K SCF for load condition “axial force in carry-over brace”
t,ax,cov-b
K SCF for load condition “axial force in reference brace”
t,ax,ref-b
K SCF for brace under basic balanced axial loading
t,b,ax
K SCF for brace under chord loading
t,b,c
K SCF for brace along line A under basic balanced axial loading (see E.1.2.1.2)
t,b ,ax
A
K SCF for brace along line E under basic balanced axial loading (see E.1.2.1.2)
t,b ,ax
E
K SCF for brace along line A under in-plane bending on the brace (see See E.1.2.2.2)
t,b ,ipb
A
K SCF for brace along line E under in-plane bending on the brace (see See E.1.2.2.2)
t,b ,ipb
E
K SCF for brace at location 3 under axial loading in carry-over brace (see D.4.2.1.2.2)
t,b ,cov,ax
K SCF for brace at location 4 under axial loading in carry-over brace (see D.4.2.1.2.2)
t,b ,cov,ax
K SCF for brace at location 3 under in-plane bending in carry-over brace (see D.4.2.2.2.2)
t,b ,cov,ipb
K SCF for brace at location 4 under in-plane bending in carry-over brace (see D.4.2.2.2.2)
t,b ,cov,ipb
K SCF for brace at location 3 under out-of-plane bending in carry-over brace (see D.4.2.3.2.2)
t,b ,cov,opb
K SCF for brace at location 4 under out-of-plane bending in carry-over brace (see D.4.2.3.2.2)
t,b ,cov,opb
K SCF for brace crown under axial loading
t,b,cr,ax
K SCF for brace crown under in-plane bending
t,b,cr,ipb
K SCF for brace crown under out-of-plane bending
t,b,cr,opb
K SCF for brace at location 3 under axial loading in reference brace (see D.4.2.1.1.2)
t,b ,ref,ax
8 © ISO 2008 – All rights reserved

K SCF for brace at location 4 under axial loading in reference brace (see D.4.2.1.1.2)
t,b ,ref,ax
K SCF for brace at location 3 under in-plane bending in reference brace (see D.4.2.2.1.2)
t,b ,ref,ipb
K SCF for brace at location 4 under in-plane bending in reference brace (see D.4.2.2.1.2)
t,b ,ref,ipb
K SCF for brace at location 3 under out-of-plane bending in reference brace (see D.4.2.3.1.2)
t,b ,ref,opb
K SCF for brace at location 4 under out-of-plane bending in reference brace (see D.4.2.3.1.2)
t,b ,ref,opb
K SCF for brace saddle under axial loading
t,b,s,ax
K SCF for brace saddle under out-of-plane bending
t,b,s,opb
K SCF for brace saddle under in-plane bending
t,b,s,ipb
K SCF for chord under basic balanced axial loading
t,ch,ax
K SCF for chord under chord loading
t,ch,ch
K SCF for chord along line B under axial loading in the brace (see E.1.2.1.1)
t,ch ,ax
B
K SCF for chord along line C under axial loading in the brace (see E.1.2.1.1)
t,ch ,ax
C
K SCF for chord along line D under axial loading in the brace (see E.1.2.1.1)
t,ch ,ax
D
K SCF for chord along line B under in-plane bending in the brace (see E.1.2.2.1)
t,ch ,ipb
B
K SCF for chord along line C under in-plane bending in the brace (see E.1.2.2.1)
t,ch ,ipb
C
K SCF for chord along line D under in-plane bending in the brace (see E.1.2.2.1)
t,ch ,ipb
D
K SCF for chord at location 1 under axial loading in carry-over brace (see D.4.2.1.2.1)
t,ch ,cov,ax
K SCF for chord at location 2 under axial loading in carry-over brace (see D.4.2.1.2.1)
t,ch ,cov,ax
K SCF for chord at location 1 under in-plane bending in carry-over brace (see D.4.2.2.2.1)
t,ch ,cov,ipb
K SCF for chord at location 2 under in-plane bending in carry-over brace (see D.4.2.2.2.1)
t,ch ,cov,ipb
K SCF for chord at location 1 under out-of-plane bending in carry-over brace (see D.4.2.3.2.1)
t,ch ,cov,opb
K SCF for chord at location 2 under out-of-plane bending in carry-over brace (see D.4.2.3.2.1)
t,ch ,cov,opb
K SCF for chord crown under axial loading
t,ch,cr,ax
K SCF for chord crown under in-plane bending
t,ch,cr,ipb
K SCF for chord crown under out-of-plane bending
t,ch,cr,opb
K SCF for chord at location 1 under axial loading in reference brace (see D.4.2.1.1.1)
t,ch ,ref,ax
K SCF for chord at location 2 under axial loading in reference brace (see D.4.2.1.1.1)
t,ch ,ref,ax
K SCF for chord at location 1 under in-plane bending in reference brace (see D.4.2.2.1.1)
t,ch ,ref,ipb
K SCF for chord at location 2 under in-plane bending in reference brace (see D.4.2.2.1.1)
t,ch ,ref,ipb
K SCF for chord at location 1 under out-of-plane bending in reference brace (see D.4.2.3.1.1)
t,ch ,ref,opb
K SCF for chord at location 2 under out-of-plane bending in reference brace (see D.4.2.3.1.1)
t,ch ,ref,opb
K SCF for chord saddle under axial loading
t,ch,s,ax
K SCF for chord saddle under in-plane bending
t,ch,s,ipb
K SCF for chord saddle under out-of-plane bending
t,ch,s,opb
K SCF for load condition “in-plane bending in brace”
t,ipb,b
K SCF for load condition “in-plane bending in chord”
t,ipb,ch
K SCF for load condition “in-plane bending in reference brace”
t,ipb,ref-b
K SCF for uniplanar K-joints
t,K
K SCF for multiplanar KK-joints
t,KK
K SCF for uniplanar CHS T-joints subjected to in-plane bending
t,T
K SCF for load condition “out-of-plane bending in brace”
t,opb,b
K SCF for load condition “out-of-plane bending in carry-over brace”
t,opb,cov-b
K SCF for load condition “out-of-plane bending in reference brace”
t,opb,ref-b
K SCF for acute angle between brace and chord axes
t,θ
L chord length between simple support or contraflexure points (see Figure D.1)
M bending moment in chord member
ch
M bending moment in carry-over brace
cov
M in-plane bending moment (see Figure D.2)
ipb
M out-of-plane bending moment (see Figure D.2)
opb
M moment of reference brace
ref
m ratio of the brace axial load in the carry-over plane to that in the reference plane (see Figure 8)
N number of cycles
N number of cycles to failure
f
n number of cycles of stress range, ∆S
i i
O overlap, (q/p) × 100
v
R stress ratio
p projected connecting length to chord of overlapping brace
q overlap length
SCF stress concentration factor
S maximum stress
max
10 © ISO 2008 – All rights reserved

S minimum stress
min
T terms used to simplify the writing of SCF equations for T-joints (see D.1.2)
i
t thickness of member subjected to fatigue-cracking test
t chord wall thickness
t thickness of brace wall i
i
W elastic section modulus of a member for in-plane bending
ipb
W elastic section modulus of a member for out-of-plane bending
opb
X terms used to simplify the writing of SCF equations for X-joints (see D.2.2)
i
α relative chord length, 2L/d or 2 L/b
0 0
β diameter or width ratio, d /d or b /b
i 0 i 0
γ chord slenderness, d /2t or b /2t
0 0 0 0
γ partial safety factor for fatigue loading
Ff
γ partial safety factor for fatigue strength
Mf
∆S stress range
∆S axial stress range
ax
∆S stress range for load condition “axial force in brace”
ax,b
∆S stress range for load condition “axial force in chord”
ax,ch
∆S stress range for load condition “axial force in carry-over brace”
ax,cov-b
∆S stress range for load condition “axial force in reference brace”
ax,ref-b
∆S hot-spot stress range
hs
∆S stress range for load condition “in-plane bending in brace”
ipb,b
∆S stress range for load condition “in-plane bending in chord”
ipb,ch
∆S stress range for load condition “in-plane bending in reference brace”
ipb,ref-b
∆S stress range for load condition “out-of-plane bending in brace”
opb,b
∆S stress range for load condition “out-of-plane bending in carry-over brace”
opb,cov-b
∆S stress range for load condition “out-of-plane bending in reference brace”
opb,ref-b
θ acute angles between brace and chord axes (in Y-, X- and K-joints)
i
τ wall thickness ratio, t /t
i 0
φ angle between planes with braces in multiplanar joints (see Figure D.9)
ψ circumferential gap parameter, φ − 2 arcsin β
5 Cumulative fatigue damage
5.1 For constant amplitude loading, it is assumed that there is no fatigue damage when the stress range is
below the constant amplitude fatigue limit defined in 3.2.
5.2 For variable amplitude loading, the stress ranges below the cut-off limit defined in 3.3 do not contribute
to fatigue damage.
5.3 When the stress ranges for a constant amplitude loaded structure, or when the maximum stress ranges
for a variable amplitude loaded structure, are above the constant amplitude fatigue limit, the cumulative
fatigue damage index, D, can be assessed using the Palmgren-Miner linear rule, for each potential crack
location; i.e.
n
i
D =
∑
N
f
where
n is the number of cycles of a particular stress range, ∆S ;
i i
N is the number of cycles to failure for that particular stress range.
f
5.4 The allowable cumulative fatigue damage index for structures in a non-aggressive environment is
generally taken as 1,0, if the effect of fatigue cracks and the possibility for inspection are taken into account by
partial safety factors.
6 Partial safety factor
6.1 The partial safety factor for fatigue loading, γ , is taken as 1,0.
Ff
6.2 The partial safety factor for fatigue strength, γ , is given in Table 1.
Mf
Table 1 — Partial safety factor for fatigue strength on hot-spot stress ranges
Fail-safe (redundant) Non fail-safe (statically determinate)
Inspection and access
component component
Periodic inspection and maintenance
1,0 1,25
(Accessible joint detail)
Periodic inspection and maintenance
1,15 1,35
(Poor accessibility detail)
7 Fatigue design procedures
7.1 Hot-spot stress method
The hot-spot stress (also called geometric stress) method relates the fatigue life of a joint to the hot-spot
stress at the weld toe rather than the nominal stress. It takes the uneven stress distribution around the
perimeter of the joint into account directly.
12 © ISO 2008 – All rights reserved

7.2 Design procedures
7.2.1 Determine the axial force ranges and bending moment ranges in the chord and braces using a
structural analysis as described in 8.1.
7.2.2 Determine the nominal stress ranges, ∆S, as specified in 8.2.
7.2.3 Determine the stress concentration factors (SCFs) as specified in 8.3.
7.2.4 Determine the hot-spot stress ranges, ∆S , as specfied in 8.4.
hs
7.2.5 Determine the permissible number of cycles for a given hot-spot stress range at a specific joint
location from a fatigue strength curve given in 8.5.
NOTE A fatigue assessment procedure is given in Annex C.
8 Fatigue strength
8.1 Member forces
8.1.1 General. For welded hollow section structures, member forces shall be obtained by analysis of the
complete structure, in which noding eccentricity of the member centrelines at the joint (see Figure 6), as well
as local joint flexibility, is taken into account. This can be achieved by one of the methods specified in 8.1.2 to
8.1.4.
8.1.2 Sophisticated three dimensional finite element modelling, where plate, shell, and solid elements
are used at the joints (appropriate for experienced analysts).
8.1.3 Simplified structural analysis using frame analysis for triangulated trusses or lattice girders.
Axial forces and bending moments in the members can be determined using a structural analysis assuming a
continuous chord and pin-ended braces (see Figure 6). This produces axial forces in the braces, and both
axial forces and bending moments in the chord. This modelling assumption is particularly appropriate for
moving loads along the chord members in structures such as cranes and bridges.
8.1.4 Rigid frame analysis for two or three dimensional Vierendeel girders.

Key
1 noding condition for most overlap connections
2 extremely stiff members
3 pin
4 noding condition for most gap connections
Figure 6 — Frame modelling assumptions
8.2 Nominal stress ranges
8.2.1 The determination of nominal stress ranges depends on the method used to determine member
forces.
8.2.2 For analysis undertaken using the approach in 8.1.2, the nominal range of stresses due to axial, ∆S ,
ax
in-plane bending, ∆S , and out-of-plane bending, ∆S , in any member can be determined by
ipb opb
Equations (1), (2), and (3), respectively:
F
ax
∆=S (1)
ax
A
M
ipb
∆=S (2)
ipb
W
ipb
M
opb
∆=S (3)
opb
W
opb
See Clause 4 for the variable definitions.
8.2.3 For analysis undertaken using the approach in 8.1.3, the nominal stress range in any member can be
determined by Equation (2) or Equation (4):
F
ax
∆=Sf (4)
ax m
A
where the magnification factor, f , is given in Table 2.
m
8.2.4 For analysis undertaken using the approach in 8.1.4, the nominal stress range in any member can be
determined by Equations (1), (2), and (3).
Table 2 — Magnification factor, f , to account for secondary bending moments in K-joints
m
Type of K-joint Chord member Brace member
CHS gap 1,5 1,3
RHS gap 1,5 1,5
RHS overlap
1,5 1,3
8.3 SCF calculations
8.3.1 If the analysis has been undertaken using the approach in 8.1.2, the SCFs can be calculated from the
analysis or using Clause 9 (for CHS joints) or Clause 10 (for RHS joints).
8.3.2 If the analysis has been undertaken using the approach in 8.1.3, the SCFs can be calculated using
Clause 9 (for CHS joints) or Clause 10 (for RHS joints).
8.3.3 If the analysis has been undertaken using the approach in 8.1.4, the SCFs can be calculated using
Clause 9 (for CHS joints) or Clause 10 (for RHS joints).
8.4 Hot-spot stress ranges
8.4.1 For analysis undertaken using the approach in 8.1.2, the hot-spot stress ranges can be obtained
directly from the analysis for each load combination. In all other cases, the following procedures should be
used to determine the hot-spot stress ranges.
14 © ISO 2008 – All rights reserved

8.4.2 The hot-spot stress range at one location under one load case is the product of the nominal stress
range and the corresponding stress concentration factor (SCF).
8.4.3 Superposition of the hot-spot stress ranges at the same location can be used for combined load cases.
8.4.4 If the position of the maximum hot-spot stress in a member, for the relevant loading condition, cannot
be determined, then the maximum SCF values shall be applied to all points around the periphery of the
member at a joint.
8.4.5 Hot-spot stress ranges shall be calculated for both the chord member and brace members.
8.4.6 Under general loading conditions, the hot-spot stress range at any location, in the chord member, is
given by the equations in 8.4.6.1 and 8.4.6.2.
8.4.6.1 For CHS XX-joints
∆=SK ∆S +K ∆S +K ∆S +K ∆S +
hs t,ax,ref-b ax,ref-b t,ipb,ref-b ipb,ref-b t,opb,ref-b opb,ref-b t,ax,ch ax,ch

KS∆+K ∆S
t,ax,cov-b ax,cov-b t,opb,cov-b obp,cov-b
8.4.6.2 For all other joints
∆=SK ∆S +K ∆S +K ∆S +K ∆S +K ∆S
hs t,ax,b ax,b t,ipb,b ipb,b t,opb,b opb,b t,ax,ch ax,ch t,ipb,ch ipb,ch
For K-joints, ∆S refers to the additional stress range determined from Figures D.5 b), E.3 b), or E.12 b).
ax,ch
8.4.7 Under general loading conditions, the hot-spot stress range at any location, in the brace member, is
given by the equations in 8.4.7.1 and 8.4.7.2.
8.4.7.1 For CHS XX-joints
∆=SK ∆S +K ∆S +K ∆S +K ∆S +
hs t,ax,ref-b ax,ref-b t,ipb,ref-b ipb,ref-b t,opb,ref-b opb,ref-b t,ax,cov-b ax,cov-b

KS∆
t,opb,cov-b opb,cov-b
8.4.7.2 For all other joints
∆=SK ∆S +K ∆S +K ∆S
hs t,ax,b ax,b t,ipb,b ipb,b t,opb,b opb,b
8.5 Fatigue strength curves
8.5.1 The fatigue strength curves (∆S −N ) are shown in Figure 7.
hs f
8.5.2 The equations for the fatigue strength curves (∆S −N ) are:
hs f
3 6
for 10 < N < 5 × 10
f
lg∆=SN(12,476− lg )+ 0,06 lgN lg( ) (5)
hs f f
3 t
or
12,476−∆3 lg S
hs
lg N = (6)
f
10− ,18lg(16/ t)
6 8
for 5 × 10 < N < 10 (variable amplitude only)
f
lg∆=SN(16,327− lg )+ 0,402 lg ( ) (7)
hs f
5 t
or
lgNS=−16,327 5 lg∆+ 2,01lg( ) (8)
fhs
t
In Equations (5) to (8), t is the thickness of applicable member being checked for fatigue cracking: for CHS
joints — 4 mm u t u 50 mm; for RHS joints — 4 mm u t u 16 mm.
8.5.3 The constant amplitude fatigue limit and cut-off limit in Figure 7 are listed in Table 3.

Key
∆S hot-spot stress range, MPa
hs
N number of cycles to failure
f
t thickness of applicable member being checked for fatigue cracking:
a) for CHS joints: 4 mm u t u 50 mm
b) for RHS joints: 4 mm u t u 16 mm
Figure 7 — Fatigue strength curves
16 © ISO 2008 – All rights reserved

Table 3 — Constant amplitude fatigue limit and cut-off limit in Figure 7
Thickness Constant amplitude fatigue limit Cut-off limit
Section type
mm MPa MPa
4 147 81
5 134 74
CHS
and 8 111 61
RHS
12 95 52
16 84 46
25 71 39
CHS 32 64 35
50 53 29
9 SCF calculations for CHS joints
9.1 Uniplanar CHS T- and Y-joints
9.1.1 Hot-spot locations are given in Figure D.1.
9.1.2 Detailed SCF equations for uniplanar CHS T- and Y-joints are given in D.1.2.1 to D.1.2.4 for the load
conditions defined in Figure D.2.
9.1.3 The factor C corresponds to the chord-end fixity. In the case of fully fixed chord ends, C is taken as
0,5. If the chord ends are pinned, C is taken as 1,0. A typical value for C is 0,7.
9.1.4 When the relative chord length, α, is less than 12, a correction factor is needed to take account of the
reduced deformation and stresses in short chords, as shown in D.1.2.
9.1.5 In the case of a diameter or width ratio β W 0,95, use SCFs for β = 0,95.
9.1.6 The validity conditions for the graphs and equations are:
diameter or width ratio
0,2 u β u 1,0
chord slenderness
15 u 2γ u64
wall thickness ratio
0,2 u τ u 1,0
relative chord length
4 u α u 40
acute angle between brace and chord axes
30° u θ u 90°
9.2 Uniplanar CHS X-joints
9.2.1 Hot-spot locations are given in Figure D.3.
9.2.2 Detailed SCF equations for uniplanar CHS X-joints are given in D.2.2 for the load conditions defined
in Figure D.4.
9.2.3 In the case of β W 0,95, use SCFs for β = 0,95.
9.2.4 The validity ranges are as specified in 9.1.6.
9.3 Uniplanar CHS K-joints with gap
9.3.1 SCFs for uniplanar CHS K-joints with gap are given for two load conditions.
9.3.1.1 Load condition 1: basic balanced axial load as defined in Figure D.5 a).
9.3.1.2 Load condition 2: chord loading (axial and bending) as defined in Figure D.5 b).
9.3.2 The SCFs for the chord of uniplanar CHS K-joints with gap under basic balanced axial loading, K ,
t,ch,ax
can be calculated using:
Kf=K
t,ch,ax c t,0,ch,ax
where K and the corresponding correction factor, f , are given in Figure D.6.
t,0,ch,ax c
9.3.3 The SCFs for the brace of uniplanar CHS K-joints with gap under basic balanced axial loading, K ,
t,b,ax
can be calculated using:
Kf=K
t,b,ax c t,0,b,ax
where K and the corresponding correction factor, f , are given in Figure D.7. Minimum values of K
t,0,b,ax c t,b,ax
are 2,64 for θ = 30°; 2,30 for θ = 45°; and 2,12 for θ = 60°.
9.3.4 The SCFs for the chord of uniplanar CHS K-joints with gap, K , under chord loading (axial and
t,ch,ch
bending) are given in Figure D.8.
9.3.5 The SCFs for the brace of uniplanar CHS K-joints with gap under chord loading (axial and bending),
K , are negligible and it can be assumed that:
t,b,ch
K = 0
t,b,ch
9.3.6 The validity conditions for the graphs are:
eccentricity
none
braces
equal
diameter or width ratio
0,3 u β u 0,6
chord slenderness
24 u 2γ u 60
18 © ISO 2008 – All rights reserved

wall thickness ratio
0,25 u τ u 1,0
acute angle between brace and chord axes
30° u θ u 60°
9.4 Multiplanar CHS XX-joints
9.4.1 Hot-spot locations are given in Figure D.9.
9.4.2 SCFs for multiplanar CHS XX-joints are given for the load conditions in 9.4.2.1 to 9.4.2.4
(see Figure D.10).
9.4.2.1 Load condition 1: axial balanced brace loading. The SCFs are given in D.4.2.1
9.4.2.2 Load condition 2: balanced in-plane bending of braces. The SCFs are given in D.4.2.2.
9.4.2.3 Load condition 3: balanced out-of-plane bending of braces. The SCFs are given in D.4.2.3.
9.4.2.4 Load condition 4: axial balanced chord loading. The SCFs are given in D.4.2.4.
9.4.3 Effects of reference brace (F , M ) and carry-over brace (F , M ) shall be combined.
ref ref cov cov
9.4.4 The validity conditions are:
eccentricity
none
braces
equal
diameter or width ratio
0,3 u β u 0,6
chord slenderness
15 u 2γ u 64
wall thickness ratio
0,25 u τ u 1,0
acute angle between brace and chord axes
θ = 90°
angle between planes with braces in multiplanar joints
φ = 90°
circumferential gap parameter
ψ W 16,2°
9.5 Multiplanar CHS KK-joints with gap
9.5.1 The SCFs for multiplanar CHS KK-joints with gap, K , can be calculated from Equation (9):
t,KK
Kf= K (9)
t,KK mc t,K
where
K is the SCF for uniplanar CHS K-joints with gap given in 9.3;
t,K
f is the multiplanar correction factor accounting for the effects of geometry and loading.
mc
9.5.2 The values of f for an angle between planes with braces in multiplanar joints, φ = 180°, are 1,0 for
mc
all values of the ratio of the brace axial load in the carry-over plane to that in the reference plane, m (see
Figure 8). The values of f for φ u 90° are given in Table 4. Interpolation is allowed for values of m between 0
mc
and −1, and for values of φ between 90° and 180°.
Table 4 — Multiplanar correction factors, f , on SCFs for CHS KK-joints with gap (φ u 90°)
mc
Chord Brace
Load case
m = +1 m = 0 m = −1 m = +1 m = 0 m = −1
Axial balanced brace loading 1,0 1,0 1,25 1,0 1,0 1,25
Chord loading 1,0 1,0 1,0 1,0 1,0 1,0
9.5.3 The validity conditions are:
eccentricity
none
braces
equal
diameter or width ratio
0,3 u β u cos θ
chord slenderness
24 u 2γ u 48
wall thickness ratio
0,25 u τ u 1,0
acute angle between brace and chord axes
30° u θ u 60°
angle between planes with braces in multiplanar joints
60° u φ u 180°
20 © ISO 2008 – All rights reserved

9.6 Minimum SCF values
9.6.1 Uniplanar CHS joints
A minimum SCF value of 2,0 is recommended unless otherwise specified such as “negligible” or “no minimum
SCF values required.”
9.6.2 Multiplanar CHS joints
When using 9.5.1, the calculated SCF for uniplanar CHS K-joints should be adopted even if it is less than 2,0.
A minimum K value of 2,0 is recommended after applying f to K .
t,KK mc t,K
Key
1 reference plane
2 carry-over plane
F load
m ratio of the brace axial load in the carry-over plane to that in the reference plane
Value of m Referred to as
1 symmetrical loading
0 reference-plane loading
−1 anti-symmetrical loading
Figure 8 — Axial balanced loading condition in multiplanar CHS KK-joints
10 SCF calculations for RHS joints
10.1 Uniplanar RHS T- and X-joints
10.1.1 Hot-spot locations (lines A to E) are given in Figure E.1.
10.1.2 Detailed SCF equations for uniplanar RHS T- and X-joints are given in E.1.2 for the load conditions
defined in Figure E.2.
10.1.3 For fillet-welded connections, multiply SCFs for the brace by 1,4.
10.1.4 For θ = 90° RHS T- and X-joints, the validity conditions are:
diameter or width ratio
0,35 u β u 1,0
chord slenderness
12,5 u 2γ u 25,0
wall thickness ratio
0,25 u τ u 1,0
10.1.5 For RHS X-joints with 40° u θ u 80°, SCFs can be determined using SCFs for θ = 90° RHS X-joints
with correction factors:
a) for chord locations
KK= 1, 2 sin θ
t,θθt,=°90
b) for brace locations
KK= 1, 2 sinθ
t,θθt,=°90
10.2 Uniplanar RHS K-joints with gap
10.2.1 SCFs for uniplanar RHS K-joints with gap are given for the following load conditions.
10.2.1.1 Load condition 1: basic balanced axial load as defined in Figure E.3 a).
10.2.1.2 Load condition 2: chord loading (axial and bending) as defined in Figure E.3 b).
10.2.2 The SCFs for the chord of a uniplanar RHS K-joint with gap under basic balanced axial loading can be
calculated from Equation (10):
Kf=K (10)
t,ch,ax c t,0,ch,ax
where
K is the reference SCF for chord under basic balanced axial loading (see Figures E.4 to E.7);
t,0,ch,ax
f is the corresponding correction factor (see Figure E.8).
c
Interpolation is allowed between the lines for other angles and between the graphs for other ratios of the gap
length to the chord wall thickness, g′, and 2γ values.
10.2.3 The SCFs for the braces of a uniplanar RHS K-joint with gap under basic balanced axial loading can
be calculated from Equation (11):
Kf=K (11)
t,b,ax c t,0,b,ax
where
K is the reference SCF for brace under basic balanced axial loading (see Figure E.9);
t,0,b,ax
f is the corresponding correction factor (see Figure E.10).
c
Interpolation is allowed between the lines for other angles and
...