1. Connection Design

2. Bolted Steel Connections
Bolts in tension
6 x 200 =1200 kN
Bolts in shear

3. Failure modes of bolts in shear
Hole bearing
Hole tearout
Bolt shear

4. Bolts in shear d + 2 mm e t Bolt shear Vr = 0.6 φ n m Ab Fu
A325M bolts: Fu = 830 MPa
A490M bolts: Fu = 1040 MPa
Hole tearout
Br = φ t n e Fu
350W steel:
Fu = 450 MPa
Hole bearing
Br = 3 φ t d n Fu d
φ = 0.67; n = number of bolts; m = number of shear planes

5. Bolts in tension threads shank d Tensile strength Tr = 0.75 φ n Ab Fu
A325M 20 mm dia
Tensile strength
Tr = 0.75 φ n Ab Fu
=0.75(0.67)(1)(314)(830) N = 131 kN

6. Bolts in tension and shear

7. Bolts in combined shear and tension
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

8. Interaction Formula
A simpler version:
Vf/Vr
Tf/Tr
1.0

9. Example Hole tear-out Bolt shear Br = φ t n e Fu Vr = 0.6 φ n m Ab Fu
d + 2 mm = 22 mm
350W steel:
Fu = 450 MPa
e = 45mm
A325M bolt: Fu = 830 MPa
t = 12mm
Hole bearing
Br = 3 φ t d n Fu
= (3)(0.67)(12)(20)(3)(450)
= 651 x 103 N = 651 kN
Hole tear-out
d = 20mm
Bolt shear
Br = φ t n e Fu
= (0.67)(12)(3)(45)(450)
= 487 x 103 N = 487 kN
Ab= πd2/4=314 mm2
Vr = 0.6 φ n m Ab Fu
= 0.6(0.67)(3)(2)(314)(830) N
= 630 kN
To avoid hole tear-out
e > 3d

10. 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

11. Contact surface of bolted parts
Values of c1 and ks
Contact surface of bolted parts ks c1
A325 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

12. Slip-critical connections in combined shear and tension

13. Welded connections
4 Times Square, NYC

14. Welded connections
Types of welds:

15. Welded truss connections

16. Welded beam connections
Full penetration groove weld
Bolted connection for web
Backing bar
Moment connection
Simple connection

17. Strength of welded connection
Tension
Base metal:
Tr = φ Ag Fy
Weld metal:
Tr = φw An Xu
φw = 0.67
Shear
Base metal:
Vr = 0.67 φw Am Fu
Weld metal:
Vr = 0.67 φw Aw Xu

18. Fillet weld strengths P L θ = 0o θ = 90o Am = b L Aw = 0.707 b L
Base metal:
Vr = 0.67 φw Am Fu
Weld metal:
Vr = 0.67 φw Aw Xu ( sin1.5θ)

19. Electrode strengths, Xu
Matching electrode strength
Xu [MPa]
Steel grades (G40.21-M)
260
300
350
380
400
480
700
410 X
550
620
820

20. Fillet weld example P Base metal: Vr = 0.67 φw Am Fu Weld metal:
Vr = 0.67 φw Aw Xu ( sin1.5θ)
6 mm fillet
200 mm P
150 mm
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 ( sin1.5θ)
= 0.67(0.67)(0.707)(6)L(480)(…..) N
= [ (150)]
= 571 kN
0.707b = 4.2 mm
b = 6 mm
Am = b L
Aw = b L

21. Example C Tr = 2 x571 = 1142 kN Lreq = [800 / 0.9] / 2 = 444 mm
6 mm fillet
400 kN
Tr = 2 x571
= kN

22. Example Mr = Tr (0.45) kNm = 756 (0.45) = 340 kNm Tr = φ A Fy
A mm dia Mr
= Tr (0.45) kNm
= 756 (0.45)
= 340 kNm Vr
16 mm
450 mm
Tr = φ A Fy
= 0.9 (16) (150) (350) N
= 756 kN
150 mm
Vr = 210/2 x 10
= 1050 kN