Bolt Shear vs Bearing vs Tearout — Failure Modes Explained

When a bolted steel connection fails, it does not fail in one way — it can fail by the bolt shearing off, by the plate material yielding around the bolt hole, or by a chunk of plate tearing out from the edge. Each failure mode has its own governing equation in AISC 360-22 J3, and understanding which one controls a given connection is essential for safe and economical design. This article explains all three, with worked numerical comparisons showing how the governing mode changes with bolt diameter, plate thickness, and edge distance.

Failure mode 1: Bolt shear (AISC J3.6)

Bolt shear is exactly what it sounds like: the bolt shank or threaded portion fails in shear as the connected plates slide relative to each other. It is the simplest failure mode to visualise and the first one most engineers check. AISC 360-22 Equation J3-1 gives the nominal shear strength per bolt:

Rn = Fnv * Ab

where:
  Fnv = nominal shear stress from AISC Table J3.2
       = 54 ksi for Group A bolts (A325, threads included)
       = 68 ksi for Group A bolts (A325, threads excluded)
       = 84 ksi for Group B bolts (A490, threads excluded)
  Ab  = nominal bolt area (based on nominal diameter)

For a 3/4 in A325-X bolt (threads excluded):
  Ab  = pi * (0.75/2)^2 = 0.442 in^2
  Rn  = 68 * 0.442 = 30.0 kips per shear plane

Design strength (LRFD):
  phi * Rn = 0.75 * 30.0 = 22.5 kips per shear plane

For a single-shear connection:      22.5 kips per bolt
For a double-shear connection:      45.0 kips per bolt

Bolt shear governs when the plate is thick and the edge distance is generous — the bolt is the weakest link. This is the most desirable failure mode from a design perspective because it is ductile: multiple bolts in a group can yield sequentially, providing visible deformation before ultimate failure.

Failure mode 2: Bearing (AISC J3.10)

Bearing failure occurs when the plate material around the bolt hole yields under the bearing pressure from the bolt shank. The plate deforms around the hole, elongating it in the direction of applied load. AISC 360-22 Equation J3-6a gives the bearing strength when deformation around the hole is a design consideration (standard case):

Rn = 2.4 * d * t * Fu     (J3-6a, deformation considered)

where:
  d   = bolt nominal diameter (in)
  t   = plate thickness (in)
  Fu  = specified minimum tensile strength of plate (ksi)

For a 3/4 in bolt in a 3/8 in plate, ASTM A572 Gr 50 (Fu = 65 ksi):
  Rn = 2.4 * 0.75 * 0.375 * 65 = 43.9 kips

Design strength (LRFD):
  phi * Rn = 0.75 * 43.9 = 32.9 kips

When deformation around the bolt hole is NOT a design consideration (e.g., the connection can tolerate 1/4 in of hole elongation without compromising the structure), use AISC Equation J3-6b which increases the bearing capacity to 3.0 _ d _ t * Fu. This gives:

Rn = 3.0 * 0.75 * 0.375 * 65 = 54.8 kips
phi * Rn = 0.75 * 54.8 = 41.1 kips

The 25% increase from J3-6a to J3-6b is significant but requires engineering judgment. In most building connections (beam end connections, splice plates), hole elongation is not a concern because the bolts bear against the hole wall regardless. In slip-critical connections or connections with precise fit-up requirements, J3-6a is appropriate.

Failure mode 3: Tearout (AISC J3.10)

Tearout is the most dramatic failure mode: the plate material in front of the bolt shears out toward the plate edge, leaving the bolt intact but the connection destroyed. Tearout capacity depends on the clear distance from the bolt hole to the plate edge in the direction of loading. AISC 360-22 Equation J3-6c:

Rn = 1.2 * Lc * t * Fu     (J3-6c)

where:
  Lc  = clear distance from bolt hole to edge, or between holes,
        in the direction of load (in)
       = Le - dh/2  for edge bolts (Le = edge distance, dh = hole diameter)
       = s - dh     for interior bolts (s = bolt spacing)

For a 3/4 in bolt at Le = 1.25 in from the plate edge:
  dh (standard hole) = 13/16 in = 0.8125 in
  Lc = 1.25 - 0.8125/2 = 1.25 - 0.406 = 0.844 in
  t  = 3/8 in, Fu = 65 ksi

  Rn = 1.2 * 0.844 * 0.375 * 65 = 24.7 kips

Design strength (LRFD):
  phi * Rn = 0.75 * 24.7 = 18.5 kips

Notice the tearout capacity of 18.5 kips is significantly lower than both the bolt shear capacity (22.5 kips) and bearing capacity (32.9 kips) for this edge distance. Tearout governs when edge distances are tight — a common condition in beam web connections where the beam depth limits available edge distance.

Head-to-head comparison: when does each mode govern?

The governing failure mode is the one with the lowest design strength. Let us compare all three for a single 3/4 in A325-X bolt in a 3/8 in A572 Gr 50 plate with Le = 1.25 in:

Tearout governs at 18.5 kips. To eliminate tearout as the governing mode, increase the edge distance. With Le = 2.0 in:

Lc = 2.0 - 0.406 = 1.594 in
Rn (tearout) = 1.2 * 1.594 * 0.375 * 65 = 46.6 kips
phi * Rn = 0.75 * 46.6 = 35.0 kips

Now the governing mode is bolt shear at 22.5 kips (most efficient design).

How plate thickness affects the governing mode

For a given bolt diameter and edge distance, the plate thickness determines whether bearing/tearout or bolt shear governs. A thin plate favours bearing and tearout; a thick plate favours bolt shear. The transition thickness t_balance where bearing capacity equals bolt shear capacity:

For 3/4 in A325-X:
  Bolt shear:    phi*Rn = 0.75 * 68 * 0.442 = 22.5 kips
  Bearing:       phi*Rn = 0.75 * 2.4 * 0.75 * t * 65 = 87.75 * t
  Tearout:       phi*Rn = 0.75 * 1.2 * Lc * t * 65 = 58.5 * Lc * t

Balance thickness for bearing (Lc not limiting):
  22.5 = 87.75 * t  -->  t = 0.256 in

Balance thickness for tearout (Le = 1.25 in, Lc = 0.844 in):
  22.5 = 58.5 * 0.844 * t  -->  t = 0.456 in

For plates thinner than approximately 1/4 in, bearing governs. For plates between 1/4 in and 7/16 in, tearout governs (at this edge distance). For plates thicker than 7/16 in, bolt shear governs. Most structural connections use plates 3/8 in to 3/4 in thick, meaning tearout and bolt shear are the most common governing modes.

Minimum edge distances per AISC J3.4

AISC 360-22 Table J3.4 prescribes minimum edge distances based on bolt diameter. These are absolute minimums, not recommendations — falling below them means the tearout equation J3-6c may not apply correctly:

Note the difference between sheared edges and thermally cut or rolled edges. Sheared edges have micro-cracks and residual stresses that reduce tearout capacity, requiring larger edge distances. Most structural plates are thermally cut, so the lower values apply.

Practical design workflow for bolted connections

When designing a bolted shear connection from scratch, the recommended sequence is:

1. Estimate the number of bolts: n = V_u / (phi * Rn_shear_per_bolt). For preliminary sizing, use the bolt shear capacity.
2. Determine edge distances: Set Le based on standard gage lines (AISC Table 1-1 provides the workable gage for each W-shape). Verify Le >= Le_min from AISC J3.4.
3. Compute tearout capacity at each bolt location: Use the actual Le. If tearout governs at any bolt, increase the edge distance or add more bolts.
4. Compute bearing capacity: For interior bolts where Le is not limiting, bearing typically governs over tearout.
5. The governing bolt capacity is the minimum of shear, bearing, and tearout at each bolt location. Multiply by the number of bolts for the group capacity.
6. Check block shear (AISC J4.3) as a separate limit state for the overall bolt group geometry.

This sequence ensures that no failure mode is overlooked. The common pitfall is checking only bolt shear and bearing, then discovering during shop drawing review that the edge distance is insufficient and tearout governs.

Comparison with other codes: AS 4100 and EN 1993

The three failure modes exist in every structural steel code, but the formulas differ:

• AS 4100:2020: Bolt shear uses phi0.62fufA with phi=0.8. Bearing uses phi3.2dftpfup with phi=0.9. Tearout is implicitly handled through the bearing check for end bolts with small edge distances. The bearing formula 3.2dftpfup is structurally equivalent to AISC's 2.4dt*Fu (converting units and phi factors).
• EN 1993-1-8: Uses the same three-fold distinction but expresses it through alpha_b and k1 reduction factors rather than separate equations. The bearing resistance Fb,Rd = (k1alpha_bfudt)/gamma_M2, where k1 and alpha_b capture the edge and end distance effects that AISC handles through the separate tearout check.

In all three codes, the physics is the same: bolt shear capacity depends on the bolt material and area; bearing capacity depends on the plate material, bolt diameter, and plate thickness; and tearout capacity depends on the edge distance. Only the safety factors and coefficient values differ.

Try the calculator

The Steel Calculator Bolted Connection Calculator computes bolt shear, bearing, tearout, and block shear per AISC 360-22 J3 for any bolt group configuration. Select AISC 360 as the design code, enter your bolt size, grade, plate thickness, and edge distances. Every limit state is checked independently with full formula substitution and clause references.

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