---------------------- | ------------- | --------------- | -------------------------------- | | Bearing-type (snug-tight) | Yes | None specified | Most building connections | | Pretensioned | No (fatigue) | AISC Table J3.1 | Fatigue, AISC 341 seismic | | Slip-critical | No (service) | AISC Table J3.1 | Oversized/slotted holes, fatigue |

Bolt strength per AISC Table J3.2

Single bolt shear capacity

The nominal shear strength per bolt is: Rn = Fnv x Ab x m, where Fnv is the nominal shear stress, Ab is the nominal bolt area, and m is the number of shear planes.

For 3/4 inch A325 single shear (threads excluded): Ab = pi(0.75)^2/4 = 0.442 sq in phi x Rn = 0.75 x 60 x 0.442 x 1 = 19.9 kips (threads excluded) phi x Rn = 0.75 x 48 x 0.442 x 1 = 15.9 kips (threads included)

When bolt threads are included in the shear plane, AISC uses a reduced nominal shear stress.

Bolt tension capacity

For 7/8 inch A325: Ab = pi(0.875)^2/4 = 0.601 sq in phi x Rnt = 0.75 x 120 x 0.601 = 54.1 kips

Bearing and tearout — AISC J3.10

For standard holes with deformation as a design consideration: Tearout: phi x Rn = 0.75 x 1.2 x Lc x t x Fu Bearing: phi x Rn = 0.75 x 2.4 x d x t x Fu phi = 0.75

Where Lc is clear distance between holes or edge, t is material thickness, Fu is tensile strength of connected material, and d is bolt diameter.

Worked example — simple shear connection

Given: W18x46 beam to W14x61 column. Reaction Vu = 55 kips (LRFD). Use four 3/4 inch A325 bolts, single shear. Clip angle: L4x4x3/8, A36 steel. Bolt spacing = 3 in center to center, edge distance = 1.5 in.

Bolt shear (threads excluded): Per bolt: phi x Rn = 0.75 x 60 x 0.442 = 19.9 kips 4 bolts: 4 x 19.9 = 79.6 kips > 55 kips → OK

Bearing on 3/8 inch angle (A36, Fu = 58 ksi): Lc = 1.5 - 0.75/2 = 1.125 in (edge bolt) Tearout (edge): 0.75 x 1.2 x 1.125 x 0.375 x 58 = 22.0 kips Bearing: 0.75 x 2.4 x 0.75 x 0.375 x 58 = 29.3 kips phi x Rn per bolt (edge) = min(22.0, 29.3) = 22.0 kips

Total 4 bolts: 22.0 + 3 x 29.3 = 109.9 kips > 55 kips → OK

Bolt installation requirements

Bolt Strength Tables — AISC 360

Bolt shear strength by diameter

Capacities shown are per bolt, single shear (phi = 0.75). For double shear, multiply by 2.

Bolt tension strength by diameter

Combined shear and tension interaction — AISC J3.7

When bolts resist both shear and tension simultaneously (e.g., bracket connections, prying), the interaction equation applies:

For bearing-type:
  Required Fnt = 1.3 x Fnt - (Fnt / phi x Fnv) x fv  ≤ Fnt

Where fv = applied shear stress, Fnt = nominal tension stress

Simplified check: the ratio (V/Vc)^2 + (T/Tc)^2 should not exceed approximately 1.0, where Vc and Tc are the individual shear and tension capacities.

Block Shear — AISC J4.3

Block shear is a combined tension and shear failure that can occur at bolt groups where a block of material tears out. It governs for connections with small edge distances or few bolts.

Block shear capacity

phi x Rn = phi x (0.6 x Fu x Anv + Ubs x Fu x Ant)  ≤ phi x (0.6 x Fy x Agv + Ubs x Fu x Ant)

Where:
  Anv = net shear area
  Ant = net tension area
  Agv = gross shear area
  Ubs = 1.0 (uniform tension stress) or 0.5 (non-uniform)
  phi = 0.75

For symmetric bolt patterns with shear through bolt holes and tension across the end, Ubs = 1.0. For coped beam connections or eccentric patterns, Ubs = 0.5 may apply.

Worked example — block shear for single-plate connection

Given: Single plate connection with (4) 3/4" A325 bolts at 3" spacing, 1.5" edge distance. Plate: 1/2" thick, A572 Gr 50 (Fy = 50 ksi, Fu = 65 ksi). Plate width = 6".

Gross shear area: Agv = 2 x (3 x 3 + 1.5) x 0.5 = 2 x 10.5 x 0.5 = 10.5 sq in Net shear area: Anv = 2 x (10.5 - 3.5 x 13/16) x 0.5 = 2 x (10.5 - 2.844) x 0.5 = 7.656 sq in Net tension area: Ant = (6 - 2 x 13/16) x 0.5 = (6 - 1.625) x 0.5 = 2.188 sq in

Tension rupture + shear yielding: phi x Rn = 0.75 x (0.6 x 65 x 7.656 + 1.0 x 65 x 2.188) = 0.75 x (298.6 + 142.2) = 330.6 kips

Tension rupture + shear fracture: phi x Rn = 0.75 x (0.6 x 50 x 10.5 + 1.0 x 65 x 2.188) = 0.75 x (315.0 + 142.2) = 342.9 kips

Governing: phi x Rn = 330.6 kips (tension rupture + shear yielding controls)

Slip-Critical Connections — AISC J3.8

Slip-critical connections prevent slip between faying surfaces under service loads. They are required for connections with oversized or slotted holes loaded in the direction of the slot, connections subject to fatigue, and where slip would compromise structural integrity.

Slip resistance formula

phi x Rn = phi x mu x Du x hsc x Tb x Ns

Where phi = 1.0 (LRFD, serviceability), mu = slip coefficient (Class A = 0.35, Class B = 0.50), Du = 1.13, hsc = hole factor (1.0 standard, 0.85 oversized, 0.70 short-slot), Tb = minimum pretension per AISC Table J3.1, Ns = number of slip planes.

Faying surface classifications

Minimum bolt pretension — AISC Table J3.1

Minimum Edge Distances — AISC Table J3.4

Minimum spacing between bolts: 2.5d (2-1/2 times the bolt diameter). Preferred spacing: 3d.

Bolt Installation Methods

Frequently Asked Questions

When should I use slip-critical vs bearing-type connections? Slip-critical connections are required when: (1) oversized or slotted holes are loaded in the slot direction, (2) fatigue loading produces stress reversal, (3) the connection is in a moment frame where slip would add to drift. For most simple shear connections, bearing-type (snug-tight) is sufficient and more economical.

What is the difference between A325 and A490 bolts? A325 (F3125 Grade A325) has Fu = 120 ksi and is the standard structural bolt. A490 (F3125 Grade A490) has Fu = 150 ksi, providing ~25% more capacity. A490 is more expensive and has hydrogen embrittlement concerns, so it is used only where the extra strength is needed.

How many bolts for a 100-kip reaction? Using 7/8" A325 single shear (threads excluded): each bolt = 27.0 kips. Need 100/27.0 = 3.7, so use 4 bolts. With threads included: 100/21.6 = 4.6, use 5 bolts. The thread condition changes the bolt count.

What is block shear failure? Block shear is a combined tear-out failure where a block of material separates from the connected part along a path that includes both shear (parallel to the force) and tension (perpendicular to the force) surfaces. It typically governs for connections with small edge distances, few bolts, or thin material.

Run This Calculation

• Bolted Connections Calculator — bolt group capacity for shear, bearing, and block shear.
• Structural Bolt Strength Table — single-bolt shear and tension capacity by grade and diameter.

Related Pages

• Bolt hole sizes reference
• Bolt spacing reference
• Bolt grades reference
• Welded connections calculator
• Steel grade reference
• How to verify calculator results

Verification

Confirm the code edition, bolt grade, hole type, plate properties, edge distances, and the assumed shear plane condition. For AS 4100, verify block shear separately because the page treats it as an adapted screening output. Then replicate the governing limit state independently by hand or in a spreadsheet.

Related Pages

• Bolt hole sizes and clearances
• Steel grade reference
• Weld Capacity per AISC and AS 4100
• Base plate and anchor design calculator
• How to verify calculator results

Disclaimer

All calculations and reported values must be independently verified by a licensed Professional Engineer before use in design, detailing, procurement, fabrication, construction, or permit submission. This tool is provided without warranty of accuracy, completeness, fitness for purpose, or project-specific code compliance. The site operator disclaims liability for any loss, damage, claim, cost, or consequence arising from use of, or reliance on, the calculator or its outputs.