43 40.5 51 63 0.75 1.3 nt nt v nv F F f F Design of (Bearing Type) Bolted Connections – Summary Objective: Design Strength n i i R Q ( Required Strength) u P Basic Design Criteria: Strength: (Use b t F and b v F values tabulated in AISC Table J3.2) Design tension strength: 0.75 ( 0.75) 0.75 b b n u b t b R F A F A Design shear strength: 0.75(0.563 ) (threads eXcluded X-type) 0.75 0.75(0.450 ) (threads iNcluded N-type) b b u s b n v s b b u s b F N A R F N A F N A Design bearing strength (of plates): 0.75(1.2 ) 0.75(2.4 ) n c u b u R L tF d tF Bolt spacing: Minimum spacing between bolts: 2 2 3 b s d (preferable 3 b d ) Edge distance: 12 value from Table J3.4 6 in e t L Combined shear and tension: 0.75 Tensile bolt stress ' 1.3 nt t nt nt v nt nv F f F F f F F Bolt shear stress v nv f F Other requirements (such as tension member design) also apply. C L S C L S
44 Bolted Connections Connection bolts: Typical bolt types: A307 (machine bolts with F t = 45 ksi); A325 and A490 (high strength bolts with F t = 90 and 113 ksi, respectively) Examples: Main mechanism : Transfer load through shear Types of bolt for design (N- or X-)Bearing Type: slip resistance at service load is unnecessary -- Snug tight or pretensioned (with no faying surface preparation) installation Slip-critical (friction-type): slip resistance at service load is desired. Slip-critical connection is desirable when the load on connections can undergo many cycles of reversal (causing fatigue), such as for bridge structures. Pretensioned installation.
45 Feeler Gages DTI’s Before bolt tightening Installation with Tension Indicators After bolt tightening Basic Bolts Installation Mechanisms: Bolt Pretensioning Mechanism Manual (Spud) Wrench Turn of Nut Method Calibrated (Impact) Wrench Installation with direct tension indicator
46 Installation of twist-off bolt Examples of simple bolted connections
47 Bearing Type Bolted Connections Assumption : Slip is allowed and both bolt shear stresses and plate bearing stresses occur Bearing Strength (of Plates) φ =0.75 Nominal bearing strength of plate: ? ? = 2?? ? 𝐹 ? 𝑝 (≈ 2?? ? 0.6𝐹 ? ) L c = clear distance, in the direction of force, between the edge of the hole and the edge of the adjacent hole or edge of material; 𝐹 ? 𝑝 = shear strength of plate ≈ 0.6 F u AISC Eq. J3-6a (pg. 16.1-127): R n = 1.2 tL c F u ≤ 2.4 F u d b t (upper limit to prevent excessive elongation) The clear distance ? ? = ? ? − ? ℎ 2 ⁄ or ? ? = ? − ? ℎ where d h = d b + 1/16 -in.
48 L e L e S S P Minimum Spacing : (AISC J3.3, pg. 16.1-122) (related to plate bearing capacity) Tear-out of plate (1) along edge, and (2) between holes Bolts in the line of force or transverse to the line of force: ? ≥ 2 2 3 ?
You've reached the end of your free preview.
Want to read all 20 pages?