introduction to connection design for steel structures
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Connection DesignConnection Design
Bolted Steel Connections Bolted Steel Connections
Bolts in tension
Bolts in shear
6 x 200 =1200 kN
Failure modes of bolts in shearFailure modes of bolts in shear
Hole tearout
Bolt shear
Hole bearing
Bolts in Bolts in shearshear
Hole bearing
Br = 3 φ t d n Fu
e
d
d + 2 mm
t
φ = 0.67; n = number of bolts; m = number of shear planes
Bolt shear
Vr = 0.6 φ n m Ab Fu
A325M bolts: Fu = 830 MPaA490M bolts: Fu = 1040 MPa
Hole tearout
Br = φ t n e Fu
350W steel: Fu = 450 MPa
Bolts in tensionBolts in tension
d
Tensile strengthTr = 0.75 φ n Ab Fu=0.75(0.67)(1)(314)(830) N = 131 kN
threads shank
A325M 20 mm dia
Bolts in tension and shearBolts in tension and shear
Bolts in combined shear and Bolts in combined shear and tensiontension
( )2222
2
56.0 ubbff FAT
mV
βϕβ ≤+
Where β = an interaction factor derived from test results= 0.69 for A325 bolts, shear plane through shank= 0.41 for A325 bolts, shear plane through threads= 0.56 for A490 bolts, shear plane through shank= 0.30 for A490 bolts, shear plane through threads
Interaction FormulaInteraction Formula• A simpler version:
( )( )
( )0.1
56.0
2
22
2
75.0
2222
2
2
2
≤+
≤+
r
f
V
r
f
FA
ubbff
TT
TmV
FATmV
r
ubb
β
βϕβφβ
Vf/Vr
Tf/Tr
1.0
1.0
ExampleExample
Hole bearing
Br = 3 φ t d n Fu= (3)(0.67)(12)(20)(3)(450)= 651 x 103 N = 651 kN
e = 45mm
d = 20mm
d + 2 mm = 22 mm
t = 12mm
Bolt shear
Vr = 0.6 φ n m Ab Fu= 0.6(0.67)(3)(2)(314)(830) N= 630 kN
A325M bolt: Fu = 830 MPa
Hole tear-outBr = φ t n e Fu= (0.67)(12)(3)(45)(450)= 487 x 103 N = 487 kN
350W steel: Fu = 450 MPa
Ab= πd2/4=314 mm2
To avoid hole tear-oute > 3d
SlipSlip--critical connectionscritical connections• When slippage of a connection during normal
service conditions (under unfactored loads) is undesirable
• Bolts are pretensioned to at least 70% of their ultimate strength
Vs = c1 ks m n (0.7)(0.75) AbFu
where ks = slip coefficient and c1 = coefficient that relates the specific initial tension and mean slip to a 5% probability of slip for bolts installed by the turn-of-the-nut method
Values of cValues of c11 and and kkss
c1Contact surface of bolted parts
ksA325 and A325M bolts
A490 and A490M bolts
Clean mill scale, or blast-cleaned with class A coatings 0.33 0.82 0.78
Blast-cleaned or blast-cleaned with class B coatings 0.50 0.89 0.85
Hot-dipped galvanized with wire brushed surfaces 0.40 0.90 0.85
SlipSlip--critical connections in critical connections in combined shear and tensioncombined shear and tension
0.19.1 ≤+ubs FnA
TVV
Welded connectionsWelded connections
4 Times Square, NYC
Welded connectionsWelded connections
Types of welds:
Welded truss connectionsWelded truss connections
Welded beam connectionsWelded beam connections
Bolted connection for web
Full penetration groove weld
Backing bar
Moment connectionSimple
connection
Strength of welded connectionStrength of welded connection
Shear
Base metal: Vr = 0.67 φw Am Fu
Weld metal: Vr = 0.67 φw Aw Xu
Tension
Base metal: Tr = φ Ag Fy
Weld metal: Tr = φw An Xu
φw = 0.67
Fillet weld Fillet weld strengthsstrengths
0.707b
b
Am = b LAw = 0.707 b L
Base metal: Vr = 0.67 φw Am Fu
Weld metal: Vr = 0.67 φw Aw Xu (1 + 0.5 sin1.5θ)
θ = 90o
θ = 0o
L
P
P
Electrode strengths, Electrode strengths, XXuu
Steel grades (G40.21-M)Matching electrode strength Xu [MPa]
260 300 350 380 400 480 700
410 X X
480 X X X X
550 X
620 X
820 X
Fillet weld exampleFillet weld example
0.707b = 4.2 mm
b = 6 mm
Am = b LAw = 0.707 b L
Weld strength:
Base metal: Pr = 0.67 φw Am Fu
= 0.67(0.67)(6)L(450) N= 1.2 L = 1.2 (550) = 660 kN
Weld metal: Pr = 0.67 φw Aw Xu (1 + 0.5 sin1.5θ)
= 0.67(0.67)(0.707)(6)L(480)(…..) N= 0.914 [400 + 1.5(150)]= 571 kN
6 mm fillet
6 mm fillet20
0 mm
P
P
150 mm
Base metal: Vr = 0.67 φw Am Fu
Weld metal: Vr = 0.67 φw Aw Xu (1 + 0.5 sin1.5θ)
Example Example
150 mm
200 mm
C
Tr = 2 x571= 1142 kN
1000 kN
400 kN
1000 kN
400 kN1142 kN
800 kN
Lreq = [800 / 0.9] / 2= 444 mm
6 mm fillet
Example Example
16 mm
150 mm
450
mm
Mr= Tr (0.45) kNm= 756 (0.45)= 340 kNm
Tr = φ A Fy= 0.9 (16) (150) (350) N= 756 kN Vr = 210/2 x 10
= 1050 kN
Vr
A325 20 mm dia
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