Block Shear Design Guide — AISC 360, AS 4100, EN 1993 & CSA S16 Worked Example

Block shear rupture can fail a bolted connection suddenly and without warning — long before bolt shear or plate bearing reach their design limits — and is particularly dangerous in shear tabs, coped beam ends, and gusset plates with tight edge distances. This guide explains the block shear check per AISC 360-22, AS 4100, EN 1993-1-8, and CSA S16:24 with a complete worked example using real dimensions and real bolt geometry. Verify every result with our free bolted connections calculator.

PRELIMINARY — NOT FOR CONSTRUCTION. All results discussed are for educational and reference use only. Must be independently verified by a licensed Professional Engineer or Structural Engineer before use in any project.

What you will learn

• The three failure surfaces that define the block shear model — tension rupture plane, shear yield planes, and shear rupture planes
• How to compute A_nt (net tension area), A_gv (gross shear area), and A_nv (net shear area) from bolt layout geometry
• The U_bs factor: when to use 0.5 vs 1.0 and how code interpretation differs between standards
• A full AISC 360 step-by-step worked example with PASS/FAIL results
• Code comparison across AISC 360, AS 4100, EN 1993-1-8, and CSA S16:24
• Common mistakes that lead to unconservative block shear designs

Copyright and standards notice

This site does not reproduce copyrighted code clauses or proprietary tables verbatim. Discussion of AISC 360, AS 4100, EN 1993-1-8, and CSA S16 here is high-level and intended to help you understand verification workflows. Always consult the official published standards for authoritative requirements.

Step 1 — The block shear failure mechanism

Block shear is unlike bolt shear or bearing. Instead of the bolt shank failing or the hole elongating, an entire block of plate material tears out. The failure surface has two distinct zones:

1. Tension plane — an area perpendicular to the applied load at the end of the bolt group, where the plate ruptures in tension
2. Shear planes — two areas parallel to the applied load (one on each side of the bolt line), where the plate simultaneously yields or ruptures in shear

The material block that separates is bounded by the bolt holes, the plate edges, and the first bolt row. The bolt group hammers against the block; the block shears out along the vertical edges and tears across the horizontal edge. This is a brittle failure mode — once initiated, there is little to no ductility before complete separation.

For seismic design (AISC 341), a ductile block shear response is preferred. This occurs when the shear yielding term (0.60 x F_y x A_gv) controls the upper bound, meaning some yielding precedes fracture. A brittle block shear occurs when the shear fracture term (0.60 x F_u x A_nv) governs — acceptable for gravity and wind-governed connections but undesirable in seismic force-resisting systems.

Step 2 — Anatomy of the block shear formula

The general block shear equation per AISC 360-22 Equation J4-5 takes two forms, and the smaller governs:

R_n = 0.60 F_u A_nv + U_bs F_u A_nt (shear rupture + tension rupture)

R_n ≤ 0.60 F_y A_gv + U_bs F_u A_nt (capped at shear yielding + tension rupture)

Where:

• F_y = specified minimum yield stress of the plate
• F_u = specified minimum tensile strength of the plate
• A_gv = gross area subject to shear (total shear plane area before subtracting holes)
• A_nv = net area subject to shear (A_gv minus hole deductions)
• A_nt = net area subject to tension (gross tension area minus hole deductions)
• U_bs = reduction factor accounting for non-uniform tension stress distribution

The design strength (LRFD) is then:

phi R_n = 0.75 x R_n

The AISC commentary explains the logic: block shear is a fracture limit state (hence phi = 0.75, the same as tension rupture), but the interaction between shear and tension on orthogonal planes requires both checks. The upper-bound expression limits the shear contribution to the yield capacity, preventing the formula from predicting unrealistically high capacities when A_gv is large but A_nt is small.

The U_bs factor — when 0.5 vs 1.0

The U_bs factor directly reduces the tension rupture contribution and can cut the block shear capacity nearly in half:

Critical rule: Coped beam ends connected with a shear tab must use U_bs = 0.5. The cope creates a non-uniform stress path from the shear tab into the reduced beam web. Many engineers mistakenly use U_bs = 1.0 for coped beams because they are accustomed to the uniform-stress assumption for standard shear tabs. This single oversight can overestimate block shear capacity by 30-50% in the coped condition.

EN 1993-1-8 does not use an explicit U_bs factor. Instead, it splits the block tearing resistance into two additive terms — one for tension and one for shear — each with its own partial safety factor (gamma_M2 for fracture, gamma_M0 for yielding). The two-term additive structure effectively serves the same purpose as the AISC cap.

AS 4100 does not provide a standalone block shear clause equivalent to AISC J4.3. Australian practice typically adapts either the AISC formulation or the EN 1993-1-8 formulation with AS 4100 resistance factors applied. Block shear should be verified independently for AS 4100 projects and treated as a screening output from automated calculators.

CSA S16:24 Clause 13.11 follows the same structural form as AISC J4.3, with phi = 0.75 and U_bs factors of 0.5 or 1.0 applied identically.

Step 3 — Define the worked example problem

We will work through a single-plate shear tab connection. This is the most common connection type in steel buildings — a vertical plate shop-welded to the supporting member (column or girder) and field-bolted to the web of the supported beam. The shear tab transfers beam-end reaction into the support. Block shear must be checked on the plate itself.

Connection geometry:

Step 3.1 — Sketch the block shear path

The tension plane runs horizontally through the top bolt, extending from one plate edge to the other. The shear planes run vertically from the tension plane down to the bottom plate edge, one on each side of the bolt line.

Step 3.2 — Compute gross tension area, A_gt

A_gt = plate_width x t = 4.50 x 0.375 = 1.6875 in^2

Step 3.3 — Compute net tension area, A_nt

Subtract one bolt hole from the gross tension area:

A_nt = (4.50 - 1 x 0.8125) x 0.375 = 3.6875 x 0.375 = 1.3828 in^2

Step 3.4 — Compute gross shear area, A_gv

Two shear planes, each running from the top bolt (tension plane) to the bottom plate edge. Length of each shear plane = end_distance + 2 x bolt_spacing = 1.50 + 3.00 + 3.00 = 7.50 in.

A_gv = 2 x 7.50 x 0.375 = 2 x 2.8125 = 5.6250 in^2

Step 3.5 — Compute net shear area, A_nv

Each shear plane crosses 1.5 bolt holes (the three bolts share the hole area — top bolt contributes half a hole to the shear plane, bottom bolt contributes half, middle bolt contributes a full hole). Total holes deducted per shear plane = 1.5.

A_nv = A_gv - 2 x 1.5 x d_h x t = 5.6250 - 2 x 1.5 x 0.8125 x 0.375 = 5.6250 - 2 x 0.4570 = 5.6250 - 0.9141 = 4.7109 in^2

Step 4 — AISC 360-22 block shear check

Step 4.1 — Select U_bs

Single-row bolt pattern with uniform tension stress distribution: U_bs = 1.0.

Step 4.2 — Calculate shear rupture + tension rupture term

R_n1 = 0.60 F_u A_nv + U_bs F_u A_nt = 0.60 x 58 x 4.7109 + 1.0 x 58 x 1.3828 = 163.94 + 80.20 = 244.14 kips

Step 4.3 — Calculate shear yielding + tension rupture term (upper bound)

R_n2 = 0.60 F_y A_gv + U_bs F_u A_nt = 0.60 x 36 x 5.6250 + 1.0 x 58 x 1.3828 = 121.50 + 80.20 = 201.70 kips

Step 4.4 — Governing nominal strength

R_n = min(244.14, 201.70) = 201.70 kips

The shear yielding term (R_n2 = 201.70 kips) governs, not the shear rupture term (R_n1 = 244.14 kips). This means the block shear response is ductile — the shear planes will yield before the tension plane ruptures. This is the preferred condition.

Step 4.5 — LRFD design strength

phi R_n = 0.75 x 201.70 = 151.28 kips

Step 4.6 — Utilization check

D/C = V_u / phi R_n = 35.0 / 151.28 = 0.231

BLOCK SHEAR: PASS at 23.1% utilization. The connection has substantial reserve capacity for this limit state.

Step 4.7 — ASD allowable strength

R_n / Omega = 201.70 / 2.00 = 100.85 kips

D/C = 35.0 / 100.85 = 0.347 — ASD also PASS.

Step 5 — Check the coped beam web (U_bs = 0.5 case)

If the connection is a coped beam end where the top flange is removed, the U_bs factor drops to 0.5 because the cope creates a non-uniform tension stress path through the beam web. Let us re-check the block shear of the beam web with U_bs = 0.5 using the same plate dimensions as the shear tab (conservatively assuming the web plate governs).

Beam: W16x36 (A992: F_y = 50 ksi, F_u = 65 ksi, t_w = 0.295 in)

The reduced web depth after coping means the block shear area is smaller. Using the same bolt layout and coped geometry with the web thickness substituted:

A_nt (web, coped): A_nt = (4.50 - 0.8125) x 0.295 = 3.6875 x 0.295 = 1.0878 in^2

A_gv (web, coped): A_gv = 2 x 7.50 x 0.295 = 2 x 2.2125 = 4.4250 in^2

A_nv (web, coped): A_nv = 4.4250 - 2 x 1.5 x 0.8125 x 0.295 = 4.4250 - 2 x 0.3593 = 4.4250 - 0.7186 = 3.7064 in^2

AISC 360 block shear with U_bs = 0.5:

R_n1 = 0.60 x 65 x 3.7064 + 0.50 x 65 x 1.0878 = 144.55 + 35.35 = 179.90 kips

R_n2 = 0.60 x 50 x 4.4250 + 0.50 x 65 x 1.0878 = 132.75 + 35.35 = 168.10 kips

R_n = min(179.90, 168.10) = 168.10 kips

phi R_n = 0.75 x 168.10 = 126.08 kips

D/C = 35.0 / 126.08 = 0.278 — BLOCK SHEAR: PASS.

Notice the difference: with U_bs = 0.5, the tension rupture contribution drops from 80.20 kips to 35.35 kips — a 56% reduction in the tension term. The overall nominal capacity drops from 201.70 kips to 168.10 kips, a 17% reduction. For thinner webs or larger copes, this reduction can flip the governing check from PASS to FAIL.

Step 6 — EN 1993-1-8 block tearing check

EN 1993-1-8 Clause 3.10.2 uses a different structural form — the "block tearing" check — but the underlying failure mechanism is identical. The design resistance is the minimum of two expressions:

V_eff,1,Rd = f_u A_nt / gamma_M2 + (1/√3) f_y A_nv / gamma_M0

V_eff,2,Rd = 0.5 f_u A_nt / gamma_M2 + (1/√3) f_y A_gv / gamma_M0

Where gamma_M0 = 1.00 and gamma_M2 = 1.25 for buildings.

Converting the worked example to metric equivalents:

• Plate: 10 mm thick, 115 mm wide, 230 mm tall
• Steel grade: S235 equivalent (f_y = 235 MPa, f_u = 360 MPa)
• 3 x M20 bolts at p1 = 75 mm, e1 = 40 mm, d0 = 22 mm
• Design shear: V_Ed = 155 kN

A_nt = (115 - 22) x 10 = 93 x 10 = 930 mm^2

A_gv = 2 x (40 + 75 + 75) x 10 = 2 x 190 x 10 = 3,800 mm^2

A_nv = 2 x (190 - 1.5 x 22) x 10 = 2 x 157 x 10 = 3,140 mm^2

V_eff,1,Rd = 360 x 930 / 1.25 + (1/√3) x 235 x 3,140 / 1.00

= 267,840 + 0.577 x 235 x 3,140

= 267,840 + 425,708

= 693,548 N = 693.5 kN

V_eff,2,Rd = 0.5 x 360 x 930 / 1.25 + (1/√3) x 235 x 3,800 / 1.00

= 133,920 + 0.577 x 235 x 3,800

= 133,920 + 515,221

= 649,141 N = 649.1 kN

V_eff,Rd = min(693.5, 649.1) = 649.1 kN

D/C = 155 / 649.1 = 0.239 — PASS.

The EN 1993 result is consistent with the AISC result: both are governed by the shear yielding upper bound, and both show similar utilization ratios. The two-partial-factor system (gamma_M0 for yielding, gamma_M2 for fracture) is captured in the formula structure directly rather than through a single phi factor.

Step 7 — AS 4100 adapted block shear check

AS 4100:2020 does not contain a standalone block shear clause analogous to AISC J4.3. Provisions in Clause 9.1.10 (ply in bearing) and the general tearout provisions supply the underlying logic, but the explicit combined tension-plus-shear rupture model must be adapted from related code provisions.

For screening and preliminary design, Australian engineers often apply the AISC block shear formulation with AS 4100 resistance factors. Using phi = 0.75 (AS 4100 Table 3.4 for bolted connections) and the same metric geometry:

V_n2 = 0.60 f_y A_gv + U_bs f_u A_nt = 0.60 x 235 x 3,800 + 1.0 x 360 x 930 = 535,800 + 334,800 = 870,600 N = 870.6 kN

phi V_n = 0.75 x 870.6 = 653.0 kN

D/C = 155 / 653.0 = 0.237 — PASS (adapted screening check).

Important: For AS 4100 projects, treat this as a screening output only. The governing result must be independently verified because AS 4100 does not provide an equivalent standalone clause. Always refer to the project's design specification for the accepted block shear methodology.

Step 8 — CSA S16:24 block shear check

CSA S16:24 Clause 13.11 follows the same structural form as AISC 360 J4.3 with phi = 0.75. Using our metric geometry with Canadian material grades (G40.21 300W: f_y = 300 MPa, f_u = 450 MPa — a higher-strength comparison):

A_nt (300W): = 930 mm^2 A_gv (300W): = 3,800 mm^2 A_nv (300W): = 3,140 mm^2

U_bs = 1.0 (uniform tension, single-row bolt pattern).

R_n1 = 0.60 x 450 x 3,140 + 1.0 x 450 x 930 = 847,800 + 418,500 = 1,266,300 N = 1,266.3 kN

R_n2 = 0.60 x 300 x 3,800 + 1.0 x 450 x 930 = 684,000 + 418,500 = 1,102,500 N = 1,102.5 kN

R_n = min(1,266.3, 1,102.5) = 1,102.5 kN

phi R_n = 0.75 x 1,102.5 = 826.9 kN

D/C = 155 / 826.9 = 0.187 — PASS.

The higher D/C margin reflects the higher material strengths in Canadian grades (300 MPa vs 235 MPa S235). When normalized for equal material grade, CSA S16 produces results within 5% of AISC 360.

Code comparison table — AISC 360 vs AS 4100 vs EN 1993-1-8 vs CSA S16

Note: Direct code-to-code capacity comparisons require normalizing material grade, resistance factors, and hole diameter definitions. The values above reflect the example parameters as defined in each code's native unit system and default material selection.

Common mistakes in block shear design

1. Using U_bs = 1.0 for coped beams. The cope creates a non-uniform stress distribution. Use U_bs = 0.5 for coped beam ends. This is the single most common block shear error and can overpredict capacity by 30-50%.

2. Forgetting to subtract bolt holes from A_gv when computing A_nv. Each shear plane that crosses bolt holes loses shear area. For a single column of bolts, each shear plane loses 0.5 holes at each end bolt plus 1.0 hole for each interior bolt — typically 1.5 holes per shear plane. Omitting this deduction overpredicts capacity.

3. Only checking one expression. Both R_n expressions must be evaluated and the minimum governs. Engineers sometimes compute only the Fu-based expression and miss the Fy-based upper bound, or vice versa.

4. Mixing net and gross areas. A_nt uses the net tension area (with holes deducted). A_gv uses the gross shear area (before hole deduction). A_nv uses the net shear area. Substituting gross for net or net for gross produces incorrect results.

5. Wrong shear plane length for end bolts. The shear plane extends from the tension plane to the plate edge. For the top bolt, include the full end distance above the bolt. For the bottom bolt, the shear plane extends below the bolt to the bottom plate edge.

6. Confusing block shear with bolt tearout. Tearout is a bearing-related limit state that checks individual bolt holes. Block shear checks the entire bolt group perimeter. Both must be checked independently — satisfying one does not guarantee the other.

7. Using the wrong phi factor. AISC 360 J4.3 uses phi = 0.75 (fracture). Do not use phi = 0.90 (yielding). The block shear limit state is classified as a rupture/fracture limit state.

8. Neglecting the coped beam web check when the shear tab passes. The shear tab plate may pass block shear while the coped beam web — with its thinner material and U_bs = 0.5 — fails. Both elements must be checked.

FAQ

What is block shear failure in steel connections?

Block shear is a combined rupture failure mode where a block of plate material tears out along a shear plane (parallel to the applied load) and a tension plane (perpendicular to the load) simultaneously. It typically governs in connections with short edge distances, thin plates, or few bolts per line. Per AISC 360-22 J4.3, the nominal block shear strength R_n = 0.60F_u A_nv + U_bs F_u A_nt (capped at 0.60F_y A_gv + U_bs F_u A_nt). The governing expression is the smaller of the two.

When does the U_bs factor change from 0.5 to 1.0?

Per AISC 360-22 J4.3, U_bs = 1.0 when the tension stress is uniform (typical for single-row bolt patterns and gusset plates with direct axial load). U_bs = 0.5 when the tension stress is non-uniform, such as when multiple rows of bolts create an eccentric tension distribution or when the connection has significant rotational flexibility. Coped beam ends with shear tabs should use U_bs = 0.5 because the cope creates a non-uniform tension stress distribution on the tension plane.

How does block shear differ from net section rupture?

Net section rupture (AISC 360 D2) is a pure tension limit state that checks only the tension plane. Block shear checks the combined tension-plus-shear failure on orthogonal planes simultaneously. A connection can satisfy net section rupture but still fail in block shear, or vice versa. Both must be verified. Block shear governs more often for short connections (few bolts per line), while net section rupture governs for long connections where the shear planes are long enough that shear is not critical.

Which code has the most conservative block shear check?

The four major standards yield similar results within approximately 5-10% for identical geometry and material. EN 1993-1-8 uses a different structural form but produces comparable capacities. AS 4100 does not have a standalone block shear clause — the check is adapted from related provisions. CSA S16:24 follows the same general formulation as AISC 360. The most conservative result for any given geometry depends on the resistance factors applied, the U_bs convention, and the partial safety factors.

When should I prefer ductile block shear over brittle block shear?

Ductile block shear (where the 0.60F_y A_gv term governs the upper bound) is preferred for seismic force-resisting systems because it provides some post-yield deformation capacity before fracture. Brittle block shear (where 0.60F_u A_nv governs) is acceptable for gravity- and wind-only connections but should be avoided in high-seismic applications. To shift from brittle to ductile, increase plate thickness (boosts A_gv relative to A_nv) or increase edge distance.

Is this guide a replacement for professional engineering judgment?

No — this is an educational reference only. All block shear calculations must be independently verified by a licensed Professional Engineer before use in any project. Results are PRELIMINARY — NOT FOR CONSTRUCTION.

Key Takeaways

• Block shear is a brittle combined rupture failure — check it on every bolted connection, especially shear tabs, coped beam ends, and gusset plates.
• Both R_n expressions must be evaluated — compute shear rupture + tension rupture AND shear yielding + tension rupture. The minimum governs.
• U_bs = 0.5 for coped beam ends. This single factor can flip a connection from PASS to FAIL. Do not use 1.0 for coped conditions.
• The 3/8" shear tab with 3 bolts passed at 23% utilization (AISC). At 35 kips demand, the block shear capacity of 151 kips (LRFD) provides substantial margin.
• EN 1993-1-8 uses the same failure model but structurally different formulas — V_eff,1,Rd and V_eff,2,Rd with partial factors gamma_M0 and gamma_M2.
• AS 4100 lacks a standalone block shear clause — treat AS 4100 block shear outputs as screening only and verify independently.
• Check both the shear tab AND the coped beam web — the thinner web with U_bs = 0.5 may govern even when the plate passes.
• Normalized for equal material grades and geometry, all four codes agree within 5-10%.

Run This Calculation

Bolted Connections Calculator — bolt shear, plate bearing, tearout, and block shear checks per AISC 360, AS 4100, EN 1993-1-8, and CSA S16. Enter your bolt layout, plate dimensions, and material grades to verify block shear alongside all other connection limit states.

Gusset Plate Calculator — Whitmore effective width, block shear rupture at bolt groups, and gusset plate buckling checks per AISC 360. For brace-to-gusset connections in braced frames and trusses.

Further Reading

• Bolted Connections Calculator
• Steel Connection Design Guide — Types, Checks & Worked Examples
• Gusset Plate Design Example — Whitmore Section, Block Shear, Buckling
• How to Calculate Bolt Capacity — AISC 360, EN 1993, AS 4100 Worked Example
• Steel Beam Splice Design — Bolted & Welded Splices per AISC 360
• EN 1993-1-8 Steel Connection Design — Bolt & Weld Checks
• AS 4100 Bolt Group Design — M20 8.8 Worked Example
• CSA S16 Design Examples — Beam, Column & Connection Worked Solutions
• Tension Member Design Reference — Yielding, Rupture, Block Shear
• Steel Plate Design Reference — Gross Yielding, Net Fracture, Block Shear
• Steel Simple Connection Design Reference
• Steel Fy & Fu Reference — Yield and Tensile Strength by Grade

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