Transcript Connection Design

Connection Design
Bolted Steel Connections
Bolts in tension
6 x 200 =1200 kN
Bolts in shear
Failure modes of bolts in shear
Hole bearing
Hole tearout
Bolt shear
Bolts in
shear
d + 2 mm
e
t
Hole tearout
d
Bolt shear
Br = φ t n e Fu
350W steel:
Fu = 450 MPa
Hole bearing
Br = 3 φ t d n Fu
Vr = 0.6 φ n m Ab Fu
A325M bolts: Fu = 830 MPa
A490M bolts: Fu = 1040 MPa
φ = 0.67; n = number of bolts; m = number of shear planes
Bolts in tension
threads shank
d
A325M 20 mm dia
Tensile strength
Tr = 0.75 φ n Ab Fu
=0.75(0.67)(1)(314)(830) N
= 131 kN
Bolts in tension and shear
Bolts in combined shear and
tension
V
2
f
2
m
  T  0.56   Ab Fu 
2
f
2
b
2
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 Formula
• A simpler version:
V
2
f
2
  T  0.56   Ab Fu 

m
2
V
f
m

T

2
r
2
f
2
2
b
 0.75b Ab Fu 
2

2
f
2
r
T
T
 1.0
Vf/Vr
1.0
Vr2
1.0
Tf/Tr
d + 2 mm = 22 mm
Example
e = 45mm
A325M bolt: Fu = 830 MPa
350W steel:
Fu = 450 MPa
t = 12mm
Hole tear-out
Br = φ t n e Fu
d = 20mm
Ab= πd2/4=314 mm2
= (0.67)(12)(3)(45)(450)
= 487 x 103 N = 487 kN Hole bearing
To avoid hole tear-out
e > 3d
Br = 3 φ t d n Fu
= (3)(0.67)(12)(20)(3)(450)
= 651 x 103 N = 651 kN
Bolt shear
Vr = 0.6 φ n m Ab Fu
= 0.6(0.67)(3)(2)(314)(830) N
= 630 kN
Slip-critical 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 c1 and ks
Contact surface of
bolted parts
ks
c1
A325 and
A325M
bolts
A490 and
A490M
bolts
Clean mill scale, or blastcleaned 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
Slip-critical connections in
combined shear and tension
V
T
 1.9
 1.0
Vs
nAb Fu
Welded connections
4 Times Square, NYC
Welded connections
Types of welds:
Welded truss connections
Welded beam connections
Full
penetration
groove
weld
Bolted
connection
for web
Backing
bar
Simple
connection
Moment
connection
Strength of welded connection
Tension
Base metal:
Tr = φ Ag Fy
Weld metal:
Tr = φw An Xu
Shear
φw = 0.67
Base metal:
Vr = 0.67 φw Am Fu
Weld metal:
Vr = 0.67 φw Aw Xu
Fillet weld
strengths
P
θ = 0o
θ = 90o
P
0.707b
b
Am = b L
Aw = 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)
Electrode strengths, Xu
Matching
electrode
strength
Xu [MPa]
Steel grades (G40.21-M)
260 300 350 380 400 480 700
410
X
X
480
X
X
550
620
820
X
X
X
X
X
Fillet weld example
Base metal:
Vr = 0.67 φw Am Fu
Weld metal:
Vr = 0.67 φw Aw Xu (1 + 0.5 sin1.5θ)
P
150 mm
6 mm fillet
6 mm fillet
P
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
0.707b = 4.2 mm
b = 6 mm
Am = b L
Aw = 0.707 b L
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
Example
1000 kN
800 kN
C
400 kN
1142 kN
Lreq = [800 / 0.9] / 2
= 444 mm
1000 kN
6 mm fillet
400 kN
Tr = 2 x571
= 1142 kN
Example
A325 20 mm dia
Vr
Mr
= Tr (0.45) kNm
= 756 (0.45)
= 340 kNm
16 mm
Tr = φ A Fy
= 0.9 (16) (150) (350) N
= 756 kN
Vr = 210/2 x 10
= 1050 kN