Bolt Shear vs Bearing — AISC 360 Section J3 Limit States

When does bolt shear control versus bolt bearing? Complete comparison of AISC 360 Section J3 limit states: threads in/out (N vs X), edge distance effects, tearout mechanism, and worked comparison for common bolted connection configurations.

Overview

PRELIMINARY — NOT FOR CONSTRUCTION. All capacities and comparisons are for educational and reference use only. Must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) before use in any project.

Bolted connections in structural steel can fail in several distinct modes. The two primary limit states are bolt shear (the bolt fractures) and bolt bearing (the base metal crushes or tears at the bolt hole). AISC 360-22 Section J3 defines the nominal strength and resistance factors for each. A ductile connection design aims for bearing (hole elongation) to govern, providing visible deformation before failure, rather than brittle bolt shear fracture.

The Two Primary Limit States

1. Bolt Shear (AISC 360 Section J3.6)

Bolt shear failure occurs when the force transferred between connected plies exceeds the shear capacity of the bolt shank. The shear plane passes through the bolt at the faying surface between connected plies.

LRFD Design Strength:

phi × R_n = phi × F_nv × A_b

where:

• phi = 0.75 (bolts)
• F_nv = nominal shear stress from AISC Table J3.2 (ksi)
• A_b = nominal bolt area (pi × d²/4) or tensile stress area, depending on thread condition

Nominal shear stress, F_nv (AISC Table J3.2):

Single shear capacity, phi*R_n (kips):

For double shear, multiply by 2.0 (but check that both shear planes engage fully).

2. Bolt Bearing (AISC 360 Section J3.10)

Bolt bearing failure occurs when the bolt bears against the hole wall and crushes or tears the base metal. There are two sub-types:

Bearing (hole elongation): The bolt bears against the plate, causing localized yielding and hole ovalization. This is the preferred ductile failure mode.

Tearout: The bolt tears through the edge of the plate, shearing out a plug of base metal in front of the bolt. This is a less ductile mode but still more desirable than bolt shear fracture.

LRFD Design Strength (per bolt):

phi = 0.75

For a bolt in a standard hole with clear distance Lc in the direction of force:

R_n = min(1.2 × Lc × t × Fu, 2.4 × d × t × Fu)

where:

• Lc = clear distance from hole edge to member edge or to adjacent hole (in.)
• t = thickness of connected material (in.)
• Fu = specified minimum tensile strength of connected material (ksi)
• d = nominal bolt diameter (in.)

The 1.2Lc term = tearout limit (edge distance dependent) The 2.4d term = bearing limit (independent of edge distance, material deformation)

For long-slotted holes with slot perpendicular to force, use 1.0 instead of 1.2.

When Each Term Governs

The tearout term (1.2 × Lc × t × Fu) governs when the bolt is close to the plate edge. The bearing term (2.4 × d × t × Fu) governs when edge distance is sufficient for full bearing.

Transition edge distance: Set 1.2 × Lc × t × Fu = 2.4 × d × t × Fu → Lc = 2d

With Leh = Lc + dh/2 = 2d + d/16 + 1/16 = 2d + d/16 + 1/16... actually standard hole = d + 1/16. Lc = Leh - dh/2.

Full bearing develops when Leh >= 1.5d (approximately). At Leh = 1.5d: Lc = 1.5d - (d + 1/16)/2 ≈ d. Then 1.2 × d × t × Fu < 2.4 × d × t × Fu, so tearout governs.

Full bearing requires Leh >= 2d + dh/2 ≈ 2.06d. At this distance, Lc = 2d, and both terms equal: 1.2 × 2d = 2.4d. Any larger edge distance and bearing (2.4d) caps the capacity.

Bolted Joint Load Path — Single Shear vs Double Shear

Single Shear

Force is transferred across one shear plane. The bolt is loaded in single shear, and each connected ply experiences bearing. This is typical for shear tab connections (beam web to single plate).

Capacity is limited by the bolt shear (one plane) and bearing/tearout in EACH ply. The governing limit state is the minimum of: bolt single shear, bearing on ply 1, tearout of ply 1, bearing on ply 2, tearout of ply 2.

Double Shear

Force is transferred across two shear planes. The center ply is sandwiched between two outer plies (or vice versa). This doubles the bolt shear capacity and distributes bearing forces across three plies. Double shear is more efficient but requires access to both sides.

Bolt capacity in double shear = 2 × single shear capacity. Bearing must be checked in EACH ply separately — the thinnest ply or smallest edge distance usually governs.

Threads In (N) vs Threads Excluded (X) — Detailed Breakdown

Condition N — Threads Included in Shear Plane

The shear plane passes through the threaded portion of the bolt. The effective shear area is the tensile stress area (root area), which is approximately 75% of the nominal bolt area.

• F_nv = 54 ksi (A325/F1852) or 68 ksi (A490/F2280)
• Uses the reduced area through the threads
• Conservative — this is the default condition unless thread exclusion is explicitly specified
• Common in shear tab connections where bolt length may not be precisely controlled

Condition X — Threads Excluded from Shear Plane

The shear plane passes through the unthreaded shank of the bolt. The full nominal bolt area resists shear.

• F_nv = 68 ksi (A325/F1852) or 84 ksi (A490/F2280)
• Uses the full nominal bolt area (pi × d²/4)
• Requires careful bolt length selection to ensure threads are outside the grip
• Adds approximately 25% shear capacity compared to Condition N for A325 bolts
• Specified when a connection requires maximum shear capacity from a given bolt diameter
• Must be noted on structural drawings and verified during erection

When to Specify Threads Excluded (X)

1. When bolt shear governs the connection and upsizing the bolt diameter is undesirable
2. For slip-critical connections in tension (bolt pretension is critical; threads-in can interfere with torque control)
3. When connection geometry allows controlled bolt length to keep threads outside the grip
4. For connections with limited bolt quantities where every kip of capacity matters

Risk of Misinterpretation

A fabricator who installs bolts with threads in the shear plane when threads are specified excluded (X) has reduced the shear capacity by approximately 20-25%. For a connection with 8 bolts, the total capacity reduction could be 30-50 kips. This is a common field error and must be caught during inspection.

Edge Distance Effects

Minimum edge distance (AISC 360 Table J3.4) prevents shear rupture of the base metal during punching or drilling. But MINIMUM edge distance does NOT provide full bearing strength.

Edge Distance and Tearout Trade-off

For the same bolt diameter and plate thickness, increasing edge distance linearly increases tearout capacity until it reaches the bearing cap (2.4 × d × t × Fu). Beyond this point, further increasing edge distance provides no additional bearing resistance.

Tearout can govern for:

• Bolts near the end of a plate (limited Lc)
• Thin plates with small edge distances
• Connections where bolt spacing is tight
• Slotted holes where net section is reduced

Worked Comparison — Shear Tab Connection

Given:

• W18x50 beam web (tw = 0.355"), A992 (Fu = 65 ksi)
• 1/2" A36 shear plate (Fy = 36 ksi, Fu = 58 ksi)
• 4 bolts: 3/4" diameter A325-N (single shear)
• Bolt spacing: 3" c/c vertical
• Edge distance to plate edge: 1.5" (perpendicular to force)
• End distance: 1.5" (parallel to force direction)

Limit State 1: Bolt Shear (J3.6)

phi × R_n per bolt = 0.75 × 54 × (pi × 0.75²/4) = 0.75 × 54 × 0.4418 = 17.9 kips

Group capacity = 4 × 17.9 = 71.6 kips

Limit State 2: Bearing on Shear Plate — Edge Bolt (J3.10)

The edge bolt has clear distance Lc = 1.5 - (0.75 + 1/16)/2 = 1.5 - 0.406 = 1.094 in.

Tearout: phi × R_n = 0.75 × 1.2 × 1.094 × 0.50 × 58 = 28.6 kips

Bearing cap: phi × R_n = 0.75 × 2.4 × 0.75 × 0.50 × 58 = 39.2 kips

Tearout governs for the edge bolt: 28.6 kips per edge bolt

Limit State 2b: Bearing on Shear Plate — Interior Bolts

Clear distance between bolts: Lc = 3.0 - (0.75 + 1/16) = 3.0 - 0.8125 = 2.188 in.

Tearout: phi × R_n = 0.75 × 1.2 × 2.188 × 0.50 × 58 = 57.2 kips

Bearing cap: phi × R_n = 0.75 × 2.4 × 0.75 × 0.50 × 58 = 39.2 kips

Bearing cap governs for interior bolts: 39.2 kips per interior bolt

Total Plate Bearing Capacity

2 edge bolts = 2 × 28.6 = 57.2 kips 2 interior bolts = 2 × 39.2 = 78.4 kips Total = 135.6 kips

Limit State 3: Bearing on Beam Web (tw = 0.355", Fu = 65 ksi)

Edge bolt Lc = same = 1.094 in. (beam web edge distance is typically >= 1.5 in.)

Tearout: phi × R_n = 0.75 × 1.2 × 1.094 × 0.355 × 65 = 22.7 kips (governs)

Bearing cap: phi × R_n = 0.75 × 2.4 × 0.75 × 0.355 × 65 = 31.2 kips

Interior bolts: bearing cap = 31.2 kips (Lc sufficient)

Total beam web bearing: 2 × 22.7 + 2 × 31.2 = 107.8 kips

Governing Limit State

Bolt shear governs at 71.6 kips. The bolts will fracture before the plate or beam web experiences bearing failure. This is a non-ductile failure mode — the connection fails suddenly without visible yielding.

Design Improvement: Threads Excluded (X)

Change to A325-X: bolt capacity = 4 × 0.75 × 68 × 0.4418 = 4 × 22.5 = 90.0 kips

Now beam web bearing governs at 107.8 kips — still bolt shear governs at 90.0 kips, but with 26% more capacity.

Wait — bolt shear is 90.0 kips, beam web bearing is 107.8 kips. Bolt shear STILL governs. To shift governing mode to bearing, either:

1. Use 5 bolts (adds 22.5 kips per bolt → 112.5 kips > 107.8 kips) — then bearing governs
2. Increase bolt diameter to 7/8" A325-N (24.3 kips/bolt × 4 = 97.2 kips, still close)
3. Accept bolt shear as the governing mode and size connection conservatively

Recommended: 5 bolts, A325-N → bolt shear = 89.5 kips, bearing governs at 107.8 kips. Ductile failure mode achieved.

Edge Distance Scenario — When Tearout Governs

Given: Same connection but end distance reduced to 1.0"

Edge bolt Lc = 1.0 - 0.406 = 0.594 in.

Plate tearout (edge bolt): phi × R_n = 0.75 × 1.2 × 0.594 × 0.50 × 58 = 15.5 kips

This is below the bolt shear capacity of 17.9 kips. Tearout now governs for the edge bolts. Total capacity:

2 × 15.5 (tearout edge) + 2 × 39.2 (bearing interior) = 109.4 kips for plate

Beam web edge bolt tearout: 0.75 × 1.2 × 0.594 × 0.355 × 65 = 12.3 kips

Total beam web: 2 × 12.3 + 2 × 31.2 = 87.0 kips

Now beam web tearout governs at 87.0 kips. The connection fails due to insufficient edge distance, NOT bolt strength. Adding more or larger bolts would not increase capacity — only increasing edge distance would help.

Choosing the Right Failure Mode

Design Strategy

1. Size bolts so shear capacity exceeds the bearing/tearout capacity of the THINNEST connected ply — bearing governs
2. Provide adequate edge distance (Leh >= 1.5d minimum, 2d preferred) to ensure bearing (2.4d cap) controls over tearout (1.2 × Lc)
3. For 3/4" bolts in 1/4" plate: bearing cap = 19.6 kips/bolt, bolt shear (A325-N) = 17.9 kips/bolt. Bolt shear governs. Either use A325-X (22.5 kips) or accept bolt shear as the governing mode for thin plates.
4. For 3/4" bolts in 3/8" plate: bearing cap = 29.4 kips/bolt, bolt shear (A325-N) = 17.9 kips/bolt. Bolt shear governs. Use A325-X (22.5 kips) — still bolt shear governs. Thicker plates shift the bottleneck to the bolt.
5. For 3/4" A325-X bolts in 1/4" plate with 1" end distance: tearout = 15.5 kips, bolt shear = 22.5 kips. Tearout governs — increase edge distance.

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Related References

• Bolt Bearing & Tearout — AISC J3.10 Tables
• Bolt Capacity Table — A325 & A490 Shear & Tension
• Bolt Hole Sizes — Standard, Oversized, Short-Slot, Long-Slot
• Bolt Spacing & Edge Distance — AISC, AS 4100
• Bolt Grades — ASTM A325, A490, F1852, F2280
• Block Shear — AISC J4.3 Rupture
• How to Verify Calculations

Design Resources

Calculator tools

• Bolted Connection Calculator
• Bolt Torque Calculator
• Gusset Plate Calculator
• Splice Connection Calculator
• End Plate Calculator

Reference pages

• Structural Bolt Strength Table
• Bolt Hole Sizes
• Bolt Spacing & Edge Distance
• Bolt Torque Chart
• Steel Connection Types

Disclaimer

This page is for educational and reference use only. It does not constitute professional engineering advice. All bolt capacities and limit state comparisons must be verified by a licensed Professional Engineer for the specific connection configuration, loading conditions, and design code applicable to your project. The site operator disclaims liability for any loss arising from the use of this information.