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 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

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

Bolts in tension and shear

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

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

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

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

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

Slip-critical connections in combined shear and tension

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 Moment connection Simple connection

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

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 (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 550 620 820

Fillet weld example P Base metal: Vr = 0.67 φw Am Fu Weld metal: Vr = 0.67 φw Aw Xu (1 + 0.5 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 (1 + 0.5 sin1.5θ) = 0.67(0.67)(0.707)(6)L(480)(…..) N = 0.914 [400 + 1.5(150)] = 571 kN 0.707b = 4.2 mm b = 6 mm Am = b L Aw = 0.707 b L

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

Example Mr = Tr (0.45) kNm = 756 (0.45) = 340 kNm Tr = φ A Fy A325 20 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