Slip-Critical Bolt with Applied Tension (AISC 360 J3.9)
How applied tension cuts the slip resistance of a slip-critical bolted joint.
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
- Applied tension on the connection Tu (kip) 30
You get
- Total clamping force Du x Tb x nb 126.6 kip
- Tension reduction factor ksc 0.762958
- Unreduced rn bolt (kip) 9.492
- Reduced rn bolt (kip) 7.242
- LRFD total (kip) 28.968
- Loss (%) 23.7042
Checked against published worked examples from: AISC 360.
Details, formula, and sources
ScopeSince tension relieves the clamping force the joint runs on. Applied tension relieves the clamping force the joint runs on, so slip resistance falls by ksc = 1 - Tu/(Du Tb nb). Four 3/4-in A325 on Class A with 30 kip of tension lose 23.7% - 37.97 kip LRFD down to 28.97. Past Du Tb nb the factor hits zero and there is no slip resistance left at all. Slip is serviceability: the J3.7 rupture check and bolt shear/bearing are separate and can pass or fail independently.
Formula or tableksc = 1 - Tu/(Du Tb nb) (Eq. J3-5a, LRFD), floored at 0; reduced slip resistance = ksc x Rn where Rn = mu Du hf Tb ns; LRFD phi = 1.00; ASD uses its own ksc = 1 - 1.5 Ta/(Du Tb nb) (Eq. J3-5b, the entered tension read as the service-level Ta), floored at 0, with Omega = 1.50; standard holes.
Source and editionAISC 360 Section J3.9 in the 2016 edition (renumbered J3.10 in 2022, where J3.9 is the slip resistance itself), slip-critical connections subject to combined tension and shear, by section number; the unreduced resistance comes from this catalog's landed slip-critical tile rather than being recomputed.
Free accessAISC 360 is available through AISC; the J3.9 interaction expression is a published code equation.
What governsEstimate. AHJ and licensed structural engineer govern.
API field namesmu, tb_kip, ns, n, hf, du, applied_tension_kip, clamp_total_kip, ksc, unreduced_rn_bolt_kip, reduced_rn_bolt_kip, lrfd_total_kip, loss_pct
- ksc interaction LRFD 1 - Tu/(Du Tb nb); ASD 1 - 1.5 Ta/(Du Tb nb); each floored at zeroAISC 360 Eq. J3-5a / J3-5b
- Mean pretension Du Tb, not the specified minimum, is the clamping force the tension is measured againstAISC 360 J3.9
- Slip only serviceability limit; shear/bearing and J3.7 rupture are separate checksAISC 360 J3.7, J3.10
- No prying prying action raises the actual bolt tension and is not modeledstated scope limit