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Members + connections = systemtransfer forces supported
by a member to others
3
ConnectionsOutlines
types of connections and their characteristics
butt weld connections: details and calculation
fillet weld connections: details and calculation
bolted connections: details and calculation
high-strength bolted connections: details andcalculation
4
Types of structural connectionsbasic types of connections
welded connectionsmolten parent metals are fused with each other being togetherelectric-arc/slag/resistance welding, gas welding
riveted connections
bolted connectionsordinary structural bolt/ high strength bolt
other connections…screw, glue…
weld rivet bolt
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Types of structural connectionswelded connections: types of welding
electric arc welding: molten weld metal (welding wire or electrode) is fused with the base metal of the members being connected
shielded metal arc welding (SMAW)Q235: E43 electrode / Q345: E50 / Q390, Q420: E55electrode matches with lower yield strength steel
submerged arc welding (SAW) : auto-/ semi-automaticH08 welding wire, with Mn flux
gas metal-arc welding (GMA): CO2
shielding gas (indoor weld)
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Types of structural connectionswelded type: shielded metal arc welding
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Types of structural connectionswelded type: submerged arc welding
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Types of structural connectionswelded type: gas metal-arc welding
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Types of structural connectionswelded connections: types of welding
electric slag weldingmolten slag + base metal + welding wire
electric resistance weldingMolten base metal + pressure
gas weldingAcetylene + oxygen + electrode
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Types of structural connectionsclassification of welds
Types of joint used: position of base metalsbutt, lap, tee, edge, corner
Types of weld madebutt weld: straight / bevel welds
fillet weld: end / side welds
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Types of structural connectionsclassification of welds
Types of weld madeContinuous weld
Intermittent weld
Welding positionFlat, horizontal, vertical, overhead
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Types of structural connectionsadvantage and disadvantage of weld connections
Efficiency: material saving and time saving
Wider range of application
More rigid, most truly continuous structures
Residual stress: rigid, stability and fatigue
Weld deformation
HAZ: brittle failure
Crack: propagation to members
Qualified: skill dependent/ qualification of welding procedurecrack, blow hole, slag inclusion, undercut, overlapincomplete penetration / fusion / filled groove
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Types of structural connectionsresidual stress
Self balance system
Not affect the static performance
Decrease the stiffness?
Decrease fatigue?
Decrease stability?
P
u
P/ yA f=
P=？u=？
＋
－－ 0.6rt yfσ =
0.3rc yfσ =
＋
－－
0.4 yfσ =
0.3 0.4 0.1− + =
0.6 0.4 1+ =
＋
－－
0.8 yfσ =
0.1
1
0.4 3 / 2 0.7+ × =
＋
－－
yfσ =
0.7
1
0.2 3 / 2 1+ × =
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Types of structural connectionsweld deformation
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Types of structural connectionsHAZ and weld crack
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Butt weld connectionsdetailing
Backup strip, back gouging and weld mending
1:2.51:2.5
Grooves and welding symbols
Run-out plate
Transition of thickness and width
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Butt weld connectionsdesign of butt welds
design resistance of butt weldsQuality grade I & II : equal to the design strength of base metalQuality grade III : decrease to 85% design strength of base metal
how to classify the quality grade of butt weldQuality grade III: visual inspectionQuality grade II: visual inspection + ultrasonic testing (20%)Quality grade I: visual inspection + ultrasonic + radiographic (100%)cross-section of butt weld(1) Area = thickness of plate (t) X effective length of weld (L)(2) With run-out plate: L = length of weld(3) Without run-out plate: L = length of weld – 2t
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Butt weld connectionsdesign of butt welds
design principle of butt weldsa. Butt weld subject to compressive force: NO NEEDb. Butt weld under repeated load: Quality grade Ic. Butt weld under tension load: Quality grade II + run-out plated. Set the butt weld in the vicinity of lower stress
Steps to design of butt weld(1) Determine the internal force at the section to be checked(2) Calculate the section properties of A, S, W, I(3) Calculate the stress(4) Check the strength of weld
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Butt weld connectionsdesign of butt welds
Typical problem using butt welds
(1) butt-welded plates subject to axial load
(2) butt-welded plates subject to axial load (inclined welds)
(3) butt welds under shear force (plates and bracket)
(4) butt welds under combined shear and moment
equivalent stress
(5) butt welds under combined tensile, shear and moment
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Fillet weld connectionsdetailing
Orthogonal fillet weld
Oblique (angle) fillet weld
End weld: transversely loaded fillet weld
Side weld: fillet weld loaded parallel to the weld’s axis
hf
hf hfhfhf
hf
hf
hf
hf
normal fillet weld concave fillet weldunequal leg fillet weld
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Fillet weld connectionsdetailing
Leg size of fillet weldMinimum: 1.5Xsqrt(tthick), prevent weld crack Maximum: 1.2tthin, prevent burn through
Length of fillet weldMinimum: 8hf & 40mm, avoid mass imperfectionMaximum: 60hf ,, avoid uneven stress distribution
Distance between two longitudinal fillet welds: shear lag
Weld symbolsFillet weld on one side / on both sideFillet weld all around joint (L, 3 or 4 sides)Fillet weld in the field
8
8
8
8
8
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Fillet weld connectionsfailure mode
Stress distributionEnd weld: tri-axial stress
(brittle failure)Side weld: mainly shear stress
(ductile failure)
Failure plane (assumption)Effective plane = failure plane
(45 degree through the throat)Effective thickness = 0.7 leg size
(weld throat)
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Fillet weld connectionsfailure mode
Failure plane and theoretical throatOrthogonal fillet weldOblique-angle fillet weld
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Fillet weld connectionsfailure mode
Failure plane and stress distribution (assumption)Normal stress perpendicular to the throat plane
Shear stress (in the plane of the throat) perpendicular to the weld axisShear stress (in the plane of the throat) parallel to the weld axis
wff3)(3 2
//22 =++ ⊥⊥ ττσ
⊥σ
⊥τ
//τ
1)75.0()75.0()( 2
2//
2
2
2
2
=++ ⊥⊥w
uw
uw
u fffττσ
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Fillet weld connectionsfailure mode
2 2 2 2 w w3 0.5 1.5 2 3 1.22f fσ τ σ σ σ σ⊥ ⊥+ ≈ + = = → =
Failure plane and stress distribution (assumption)
wff3)(3 2
//22 =++ ⊥⊥ ττσ
2 2 w w//3 3 3 f fτ τ τ= = → =
τ ⊥
σ ⊥ σ
//τ τ=
//τσ ⊥
τ ⊥
End weld: larger strength and rigid, less deformation ability
Side weld: 22% less than strength of end weldlarger deformation ability
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Fillet weld connectionssimplified method
wff3)(3 2
//22 =++ ⊥⊥ ττσ
simplified method for design resistance of fillet weld
amplification factor for weld strength perpendicular to the weld axis, taken as 1.22 for static loading and 1.0 for dynamic loading
wf
2f
2
f
f )( f≤+τβσ
fβ
wff design strength of fillet weld (same for shear, tension and compression)
For applied force N perpendicular to the weld axis
stress on the failure plane
f w e/N l hσ =
f w e/V l hτ =
For applied force V parallel to the weld axis//τ
τ ⊥ σ ⊥
fN σ→
fV τ→
w f2l l h= −e f0.7h h=
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Fillet weld connectionsprocedure of fillet weld design
Focus on the distinguishing of stress perpendicular to the weld axisand stress parallel to the weld axis
Calculation of weld section properties, A, S, I, W (weld length)
Centroid of welds coincides with that of members
Axial force, shear force or combined axial and shear forceCombined bending moment, axial and shear forcesCombined torsional moment, axial and shear forces
Stress calculation under single force
wf
2f
2
f
f )( f≤+τβσ
Analysis of internal forces at weld connection
Superposition of stress components at critical point, then check with practical equation
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Fillet weld connectionstypical problem (1)
Axially loaded weld connections
wf
2f
2
f
f )( f≤+τβσ
N
(1) Internal force1N
V
θθsin1 NN =
θcosNV =
(2) Weld stress
f
11f A
Nlh
N
we
==∑
σ
ff A
Vlh
V
we
==∑
τ
(3) Stress check
wf
f
0 ,0 fAN
≤=θ
wff
f
0 ,90 fAN βθ ≤=
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Fillet weld connectionstypical problem (2)
Axially loaded weld connections ( C & Angle)
(1) 3 sides around welds (cover plate of flange)
wf
f 1 e1 2 f2 e22( )N f
l h l h hβ≤
+ −1l2l2l
NN
(2) 2 sides welds
(4) L-shape welds (angle) ?
NN1 f1,l h
2 f2,l h
1e2e b
1 2 1( / )N e b N k N= =Internal force
2 1 2( / )N e b N k N= =0.7
0.3 0.25
0.750.65
0.35
(root)(toe)
1k2k
(3) 3 sides around welds (angle)NN
1 1 30.5N k N N= −
2 2 30.5N k N N= −
Internal force
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Fillet weld connectionstypical problem (3)
, , ,N V N V M⇒
Nfx
f
NA
σ =
Vfy
fw
VA
τ ==
weld connections subject to bending moment, axial and shear forces
(1) Internal force
(2) Weld stress
(3) Stress check
N
V
M
V
x
y
Mfx
fx
M yI
σ =
N M2 V 2 wfx fx
fy ff
( ) ( ) fσ σ τβ+
+ ≤
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assumption：(1) The connected plate is
perfectly rigid, thus the welds are assumed to be perfectly elastic
(2)
Fillet weld connectionstypical problem (4)
weld connections subject to torsional moment, axial and shear forces
m
mr rτ τ
=
m
m
dF dA rdArττ= =
Resultant force for any micro-element
Torsional moment about weld centroid for the micro-element
2m
m
dM rdF r dArτ
= =
Total torsional moment for the weld connection
m m fyf xf
m m
( ) JI Ir rτ τ
= + =
2mi i
m
M rdF r dArτ
= =∫ ∫2 2m
m
( )x y dArτ
= +∫
mτmr
r
τdA
x
y
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Fillet weld connectionstypical problem (4)
weld connections subject to torsional moment, axial and shear forces
y
x
mτmr
Mfxτ
MMfyσ
Nfxτ
Vfyσ
N
Vθ
(1) Stress calculation for welds subject to torsional moment and axially force(taken Q point, how about S point?)
QM mfx m
f f
sin sinMr MyJ J
τ τ θ θ= = =
Mfy
f
MxJ
σ =
Nfx
wi ei f
N Nl h A
τ = =∑
Vfy
f
VA
σ =
V Mfy fy 2 N M 2 w
fx fx ff
( ) ( ) fσ σ
τ τβ−
+ + ≤
S
(2) Stress checkcritical point, S or Q?
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Fillet weld connectionscomparison of butt weld with fillet weld
Butt weldgroove preparation
less filler metal, just a few run-out plate
computing method of weld is similar with that of base metal
design strength of weld equals to base metal
base metal-weld-base metal connect smoothly, less stress concentration
Fillet weldNo groove
pretty much gusset plates
completely different in stress calculation compared to base metal
design strength of weld is less than base metal
performance is worse than that of butt welds
Manufacture
Weld strength
Dynamic performance
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Fasteners connectionscharacteristics
Characteristics
MachiningPosition and hole machining: drill, punchSurface treatment (for slip-resistant connection)Assembly: snug-tight or pretensioned
Ease to erect on site (less skill / facility dependent)Fatigue resistance (for slip-resistant connection)Easy to prevent the propagation of crackEasy to realize the removable structuresMaterial and time wasteStrongly depend on the machining accuracyPartially damnifying the base metal
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Common-bolt connectionsintroduction
Types of boltUnfinished, ordinary or common boltHigh-strength bolt (pretensioned)
Bolt gradeGrade 4.6, 4.8: Q235BF (Grade C bolt)Grade 5.6, 8.8: quality carbon steel (Grade A, B bolt)
heat-treatment
Hexagonal bolt Twist-ff bolt
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Common-bolt connectionsintroduction
Drilled hole dimensionHole dimension = bolt diameter + 1~1.5mmGrade A, B bolt: hole quality, hole size deviation +0.25mmGrade C bolt: relatively large tolerances in shank, thread dimensions
and holes, hole size deviation + 1mm
Load transferbolt loaded shear force
bolt loaded tension
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Common-bolt connectionsbolt for shear transfer
Behaviour mechanism (load transfer)friction plate shear off the bolt and
the bolt push or bear against the hole
Failure modeShearing of the bolt (calc.)
Bearing of the bolt/hole (calc.)
Tension failure of plate (calc.)
Shearing out of part plate (calc. & detail)
Bending of bolt (detail) 5l d≤
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Common-bolt connectionsbolt for shear transfer
Design resistance for individual bolt subjected to shear
bv
2v
bv 4
fdnN ⋅⋅⋅=π
bc
bc fdtN ⋅⋅= ∑
},min{][ bc
bv
bv NNN =
(1) Shear resistance (shear plane)
(2) Bearing resistance (thickness for bearing same-direction force)
F F/2
F/2
F/2
F/2
F/2F/2
(3) Design resistance for individual bolt
39
Common-bolt connectionsbolt for tension transfer
Behaviour mechanism (load transfer)The two contact plates tend to expand
and the bolt are tensioned
Prying actionHow prying action affect the internal force of the bolt?
F0 .5 F
0 .5 F
F0 .5 F P+
P
P0 .5 F P+
Design resistance for individual bolt subjected to tensionb
t2e
bt 4
fdN ⋅⋅=π
Measure to reduce prying action
Tension increase in bolt decrease strength of boltFailure plane: effective section in thread
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Common-bolt connectionsspacing and edge distance of bolts
Behaviour mechanism (load transfer)
Specification of spacing allowance (hole-size based)requirement of capacity: cutting off and bucklingrequirement of detail: anti-corrosionrequirement of construction: room for wrench
Pitch: the center-to-center distance of bolts in a direction parallel to the member axisGage: the center-to-center distance of bolt lines perpendicular to the member axisEdge distance: the distance from the center of bolt to the adjacent edge of a member
Net area forregular and staggered spacing bolt
41
Common-bolt connectionstypical problem (1)
Uniformly shearing boltsLong joint: uneven shear force in each boltElastic and plastic period: uneven uniform
Procedure of design(1) determine the shear force on the connect plane(2) calculate the shear force of each bold endured(3) ascertain the design resistance for individual bolt:
• single shear, double shear or multiple shear?• shear resistance or bearing resistance?• long joint need to reduce resistance by a reduction factor?
1 01.1 /150l dη = −1.0η =
0.7η =
1 0/ 15l d ≤
b bV V[ ] [ ]N Nη→
1 015 / 60l d< ≤
1 0/ 60l d ≥
(4) check the capacity of net section
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Common-bolt connectionstypical problem (2)
Bolted eccentric connection with torsional moment
x
yMxN
M
NxN
N
V
VyN
MyN
assumption：(1) The bolt is perfectly elastic and the connected plate is perfectly rigid(2) The shear stress of a bolt at a centroidal distance d is proportional to d
Mx 2 2
i i( )M yNx y
=+∑
My 2 2
i i( )M xNx y
=+∑
Procedure of designSame as procedure mentioned before, and pay attention to the superposition of shear force under torsion with that under axial load
bV
My
Mx NNN ][)()( 22 ≤+
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Common-bolt connectionstypical problem (3)
Bolted connection subjected to tension
assumption：(1) Location of neutral axis?(2) The tension force of a bolt at a centroid
distance d is proportional to d
Bolted connection subjected to bending moment
Capacity check: (maximum loaded bolt)
M b11 t2
i
MyN Ny
= ≤∑
44
Common-bolt connectionstypical problem (4)
Bolted connection subjected to combined tension and bending moment
1 ty
'1y
The tension force of a bolt depends on the location of the neutral axis.
(1) Assume the neutral axis locates the centroid of bolt connection
M 1c1c 2
i
M yNy
= −∑
N NNn
=
(2) If , the assumption is ok and the critical tension force
M N1c 0N N+ ≥
M b1 t1 t2
i
M y NN Ny n
= + ≤∑
1
'M b
1 t' 2i
( )M N e yN N
y+
= ≤∑
M N1c 0N N+ <(3) If , the neutral axis locates the
bottom line of bolts, the critical tension force
Note: y value in item (2) & (3) away from corresponding neutral axis
45
Common-bolt connectionstypical problem (5)
1)()( 2bt
t2bv
v ≤+NN
NN
Bolted connection subjected to combined shear and tension forces
(1) Correlation equation
(2) Shear rest to avoid the shear force in bolt
Q: replacing with is ok?Q: do we need radical sign?
bcv NN ≤
bVN b
CN
Q: weld detail of the rest?
46
High-strength bolt connectionsintroduction
Machining of high-strength boltHole: hole size is larger than shank 1~1.5mm (bearing-type bolt)
1.5~2mm(slip-resistant bolt)Surface treatment: only for slip-resistant boltPretensioned: both slip-resistant and bearing-type bolt
High-strength boltpretensioned
High-strength bolt with large hexagon head
Tor-shear type high-strength bolt
47
High-strength bolt connectionsintroduction
Behaviour mechanism for shear transfer
F
u
design criteria for bearing-type high-strength bolt
common-bolt
FF
FF
design criteria for slip-resistant high-strength bolt
Behaviour mechanism for tension transfer
bc AANPP
++=
1f
48
},4
min{][ bc
bv
2v
bv ∑ ⋅⋅⋅= fdtfdnN π
high-strength bolt connectionsbolt for shear transfer
PnN ⋅⋅= μfbv 9.0
design resistance for individual slip-critical bolt subjected to shear
(1) 0.9―reciporical of resistance factor (1/1.111)
(2) ―number of slip planes
(3) ―Slip coefficient for different surface (Table8-7)
(4) ―pretensioned force (Table 8-8)
fnμP
eueu AfAfP 6075.02.1/9.09.09.0 =××××=
Q: do we need to check the bearing of the hole?
design resistance for individual bearing-type bolt subjected to shear
49
high-strength bolt connectionsbolt for tension transfer
design resistance for individual slip-critical bolt subjected to tension
Q: why use 0.8 reduction? (for the sake of shear transfer)
design resistance for individual bearing-type bolt subjected to tension
PN 8.0bt =
bt
2e
bt 4
fdN ⋅⋅=π
Q: why same as the common-bolt capacity?
50
High-strength bolt connectionstypical problem (1)
Uniformly shearing boltsSlip-critical connection:
- shearing of bolt- capacity of net section:
Bearing-type connection: same as common bolt
Bolted connection subjected to combined shear and tension forces
N1
' 5.0 nnNNN ××−=
1)()( 2bt
t2bv
v ≤+NN
NN
2.1/bcv NN ≤
1bt
tbv
v ≤+NN
NN
)25.19.0 tfbv NPnN −⋅⋅= （μ
(GB50017-2003)
(GBJ17-88)
For slip-critical connection: For bearing-type connection:
Q: why use 1.2 not as common-bolt?
51
High-strength bolt connectionstypical problem (2)
Bolted eccentric connection with torsional moment/shearInternal force at each bolt is ascertained as common bolt Check the capacity: slip-critical or bearing-type bolt?
Bolted connection subjected to bending moment
As subjected to bending moment
Test result: external force is smaller Tongji’s is better; while larger, Chen’s better
Internal force at each bolt is as common bolt Location of neutral axis:- Tongji: at centroid,
max. tension in bolt less 0.8P, and the connected plateis always in compression
- Chen Shao-fan: as common bolt
Bolted connection subjected to bending moment & tension
52
Question:
53
Question:
TP
P
？
？N
0 d y R/( 3 ) /N b d t f f γ− ≤ =
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