Slip-Critical Bolt Design Strength (AISC 360 J3.8)
Where slip cannot be tolerated - oversized holes, fatigue, load reversal - the joint is governed by friction, not shear.
Example
You enter
- Slip coefficient mu (0.30 A / 0.50 B) 0.3
- Minimum pretension Tb (kip, Table J3.1) 28
- Slip planes ns (1 single, 2 double) 1
- Number of bolts 4
- Filler factor hf 1
- Du multiplier 1.13
You get
- Rn bolt (kip) 9.492
- ASD bolt (kip) 6.328
- Connection total (LRFD) 38.0 kip
- Connection total (ASD) 25.3 kip
Details, formula, and sources
Rn = mu Du hf Tb ns with mu 0.30 (Class A) or 0.50 (Class B blast-cleaned), Du 1.13, and the Table J3.1 pretension. A 3/4 in A325 on a Class A surface resists 9.49 kip per bolt (6.33 ASD); go Class B in double shear and one bolt jumps 3.3x to 31.6 kip - surface prep and a second plane are the levers. The strength-level bolt shear and bearing check must also pass. A design aid, not the engineer of record's stamped design.
Rn_bolt = mu Du hf Tb ns; ASD = Rn/1.50, LRFD = 1.00 Rn (standard holes); totals = n x per-bolt.
The AISC 360-22 J3.8 slip-critical connection resistance with the Class A/B slip coefficients, Du = 1.13, the Table J3.1 minimum pretension, and the standard-hole phi = 1.00 / Omega = 1.50, by name.
AISC 360 is free to read at aisc.org (Specification for Structural Steel Buildings); the J3.8 provision and Table J3.1 pretensions are in the published specification.
Estimate. AHJ and licensed professional govern.
Field names used by the API: mu, tb_kip, ns, n, hf, du, rn_bolt_kip, asd_bolt_kip, lrfd_total_kip, asd_total_kip
- Slip resistance mu Du hf Tb per slip plane; friction, not shear, governs the serviceability of the jointAISC 360-22 J3.8
- Surface class mu = 0.30 unpainted mill scale (Class A); 0.50 blast-cleaned (Class B)AISC 360-22 J3.8
- Also check strength the bearing-type shear and bearing/tearout limit states still applyAISC 360-22 J3.8 user note