----------------- | ----------- | ---------- | ----------- | -------- | | Bolt shear + bearing | J3.6, J3.10 | Cl 9.3 | Cl 3.6.1 | Cl 13.12 | | Weld strength | J2.2 | Cl 9.7 | Cl 4.5 | Cl 13.13 | | Block shear | J4.3 | Cl 9.2.2 | Cl 3.10.2 | Cl 13.11 | | Prying action | J3.6 | Cl 9.3.2.2 | Cl 6.2.4 | Cl 13.12 | | Shear tab flexure | J4.5 | Cl 9.3.1 | Cl 6.2 | Cl 13.10 | | Web local yielding | J10.2 | Cl 5.13 | Cl 6.2.6.2 | Cl 14.3 | | Web crippling | J10.3 | Cl 5.13 | Cl 6.2.6.3 | Cl 14.3 |

Prying Action Overview

Prying action occurs in tension-loaded bolted connections (such as end plates) where bolt tension induces flexure in the connected plate, amplifying the actual tension demand on the bolts. AISC 360-22 Section J3.6 provides the prying action equations. The key parameters are the plate thickness (tp), bolt gauge (g), and the ratio of flange flexural stiffness to bolt axial stiffness. Increasing plate thickness is the most effective way to reduce prying amplification.

Design Guidance

Key Design Parameters

When performing structural steel design calculations, the following parameters govern the design:

• Material properties: Yield strength (Fy) and tensile strength (Fu) determine section capacity. For US projects, common grades include A992 (Fy=50 ksi) for W-shapes and A36 (Fy=36 ksi) for angles and plates.
• Design method: LRFD (Load and Resistance Factor Design) or ASD (Allowable Stress Design). LRFD applies load factors >1.0 and resistance factors <1.0 for consistent reliability across limit states.
• Load combinations: Per ASCE 7-22, the governing combination depends on the direction and magnitude of each load type. Typically 1.2D + 1.6L governs for gravity-dominated cases.
• Limit states: Strength (ultimate) and serviceability (deflection, vibration). Both must be checked per the applicable design code.
• Applicable codes: AISC 360-22 (US), EN 1993-1-1 (EU), AS 4100 (Australia), CSA S16 (Canada).

Design Procedure

1. Establish design criteria: code edition, material grade, design method (LRFD/ASD)
2. Determine loads and applicable load combinations
3. Analyze structure for internal forces (axial, shear, moment, torsion)
4. Check member strength for all applicable limit states
5. Verify serviceability criteria (deflection, drift, vibration)
6. Detail connections to transfer calculated forces

Worked Example

Problem: Design a structural element for the following conditions:

Span/Height: 15 ft | Load: 50 kips (factored) | Section: W12×65 (A992, Fy=50 ksi) | Code: AISC 360-22 LRFD

Solution:

• Demand: Pu = 50 kips (axial compression)
• Section properties: A = 19.1 in², rx = 5.28 in, ry = 3.02 in
• Slenderness: KL/r = 1.0 × 15 × 12 / 3.02 = 59.6 (controls about weak axis)
• Critical stress: Fcr per AISC Eq E3-2 (intermediate slenderness range)
• Design strength: φcPn = 0.9 × Fcr × Ag — Verify against applied load
• Interaction: Check combined forces per AISC Chapter H if applicable

Result: Section is adequate if φcPn ≥ Pu (50 kips).

Frequently Asked Questions

What design codes does this calculator support?

This calculator supports AISC 360-22 (US LRFD and ASD), EN 1993-1-1 (Eurocode 3), AS 4100 (Australia), and CSA S16 (Canada). Each code edition is verified against the respective design standard. Select your governing code in the calculator interface before entering loads.

How accurate are the results from this calculator?

Results are verified against published design examples and textbook solutions. The calculation engine uses the exact code provisions from the applicable standard. Always verify critical results independently and have designs reviewed by a licensed Professional Engineer. Results are preliminary until independently verified.

Can I save and export my calculations?

Registered users can save calculations to their account for later reference. Currently 10 calculations per hour and 50 per day are available on the free tier. Pro subscription ($49/month) increases limits to 500 calculations per month with PDF export capability.

Frequently Asked Questions

What is the most common governing limit state for steel connections? For shear connections, bolt shear or bearing at the bolt holes typically governs. For moment connections, either weld strength at the beam flange or prying action in the end plate governs. Block shear frequently governs in gusset plates and coped beams. Always check all applicable limit states — the weakest link determines the connection capacity.

How does block shear differ from bolt bearing failure? Block shear is a rupture failure along a path combining shear planes (parallel to load) and tension planes (perpendicular to load), causing a block of material to tear out. Bolt bearing is a localized crushing failure around a single bolt hole. Block shear typically governs when bolt groups are close to a free edge; bearing governs for interior bolts with adequate edge distance.

What is the minimum edge distance for bolt holes in structural steel? AISC 360-22 Table J3.4 specifies minimum edge distances by bolt diameter and edge type (sheared or rolled/plasma-cut). For 3/4-inch bolts, minimum edge distance is 1-1/8 inches for sheared edges and 7/8 inches for rolled edges. These are absolute minimums — practical edge distances for full bearing capacity are 2-3 times the bolt diameter.

Is this connection check calculator free? Yes, completely free with unlimited calculations. No registration required.

Block Shear vs Net Section Fracture

Block shear rupture and net section fracture are two distinct tension failure modes that frequently control the capacity of bolted steel connections. While both involve fracture across the net section, their mechanics, governing equations, and design sensitivities differ significantly.

Block Shear Rupture (AISC 360-22 Section J4.3)

Block shear is a limit state where a block of material tears out along a path that combines shear planes (parallel to the applied force) and a tension plane (perpendicular to the applied force). It occurs when bolt groups are relatively compact and positioned near a member edge.

Governing equation (AISC 360-22 Eq J4-5): Rn = 0.60 x Fu x Anv + Ubs x Fu x Ant <= 0.60 x Fy x Agv + Ubs x Fu x Ant

Where:

• Anv = net area in shear (gross shear area minus bolt hole deductions)
• Ant = net area in tension
• Agv = gross shear area
• Ubs = 1.0 for uniform tension stress (most cases), 0.5 for non-uniform
• Fu x Ant term captures tension fracture contribution on the perpendicular face

Worked comparison — block shear vs net section:

Consider a 3/8-inch thick A36 plate (Fu = 58 ksi) with a single line of three 3/4-inch A325 bolts at 3-inch pitch spaced 1-1/2 inches from the plate edge. Applied tension = 45 kips.

Block shear check:

• Shear planes: 2 planes x (3" + 3" = 6 in effective length)
• Agv = 2 x 6 x 0.375 = 4.50 in^2
• Anv = Agv - 2.5 holes x (13/16 in effective hole) x 0.375 = 4.50 - 0.76 = 3.74 in^2
• Ant = (1.5 in edge - 0.5 hole) x 0.375 = 0.375 in^2
• Rn1 = 0.60 x 58 x 3.74 + 1.0 x 58 x 0.375 = 130.2 + 21.8 = 152.0 kips
• Rn2 = 0.60 x 36 x 4.50 + 1.0 x 58 x 0.375 = 97.2 + 21.8 = 119.0 kips
• Rn = min(152.0, 119.0) = 119.0 kips (shear yielding controls the upper bound)
• phi x Rn = 0.75 x 119.0 = 89.3 kips > 45 kips — OK

Net section fracture check (AISC 360-22 Section D2):

• An = Ag - n_holes x d_hole x t = (1.5 x 0.375) - 1 x 0.8125 x 0.375 = 0.563 - 0.305 = 0.258 in^2
• Ae = An x U (U = 1.0 for this case, direct tension to all elements)
• Rn = Fu x Ae = 58 x 0.258 = 14.9 kips
• phi x Rn = 0.75 x 14.9 = 11.2 kips << 45 kips — FAILS

When Each Mode Governs

Ductile vs Brittle Failure Considerations

Block shear can be designed for either ductile or brittle behavior:

• Ductile block shear: The shear yielding term (0.60 x Fy x Agv) is the controlling upper bound, meaning some yielding occurs before fracture. This is preferred for seismic applications.
• Brittle block shear: The shear fracture term (0.60 x Fu x Anv) controls, meaning failure occurs suddenly with little warning. This is acceptable for wind-only or gravity-only connections but should be avoided in seismic force-resisting systems.

Net section fracture is always a brittle failure mode — there is no yielding precursor. For this reason, AISC 360 requires that the design tensile strength based on net section fracture (phi x Fu x Ae) be at least as large as the design yield strength (phi x Fy x Ag) to ensure yielding precedes fracture. A commonly overlooked check: if Ae/Ag < Fy/Fu, net section fracture governs before gross section yield.

Design Strategies to Prevent Block Shear and Net Section Fracture

1. Increase edge distance: Moving bolts further from the edge increases both shear plane length and tension plane width.
2. Stagger bolt rows: Staggering bolts increases net area for the net section check (AISC 360 Section B4.3b).
3. Increase plate thickness: Both block shear and net section capacity scale linearly with thickness.
4. Use larger bolt spacing: Increases shear plane length for block shear resistance.
5. Specify a higher Fu/Fy ratio steel: A572 Gr 50 (Fu/Fy = 65/50 = 1.30) provides better post-yield fracture resistance than A36 (Fu/Fy = 58/36 = 1.61) for net section, but A36's lower Fy reduces shear yielding capacity for block shear.

Related pages

• Steel bolted connection design
• Weld group calculator
• Tension member design
• Bolt bearing reference
• Welded connection reference
• Bolt spacing and edge distance
• Bolt group capacity (EU)
• Moment connection design (UK)

Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice. All structural designs must be verified by a licensed Professional Engineer (PE) or Structural Engineer (SE). The site operator disclaims liability for any loss or damage arising from the use of this page.