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Calcs.com
Australia
AS 4100:2020AS 4100:1998

Steel Bolt

Structural engineers in Australia designing bolted steel connections to the current AS 4100:2020. Handles arbitrary bolt group geometry under shear, tension, in-plane moment, and out-of-plane moment with full ULS and serviceability checks.

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What it calculates

Design and analyse bolt groups under shear, tension, and combined loading to AS 4100:2020. The elastic method distributes applied forces across an arbitrary bolt layout and checks all ULS and serviceability limit states for the critical bolt.

Code standards

  • AS 4100:2020

How it calculates

The Steel Bolt (AS 4100:2020) calculator applies the elastic method to distribute applied loads across the bolt group and then verifies each limit state in AS 4100:2020 Clause 9 for the critical bolt.

Load distribution

Applied design actions (shear V*, tension N*, in-plane moment M_z, and out-of-plane moment M_x) are resolved at the centroid of the bolt group. The centroid is computed assuming uniform bolt area.

For in-plane loads, the elastic method resolves direct shear and torsional shear components using the polar moment of inertia I_z of the bolt group. The critical bolt is identified as the one carrying the highest resultant from the vector sum of all components.

Bolt shear capacity (Clause 9.3.2)

Nominal shear capacity V_f per shear plane depends on the location of the shear plane relative to the threads:

  • Through the threaded portion: V_f = 0.62 × f_uf × A_s
  • Through the unthreaded shank: V_f = 0.62 × f_uf × A_o

Total shear capacity sums across all shear planes. Design capacity: V_d,f = phi_b × V_f.

Utilization = V*_f / V_d,f ≤ 1.0

Bolt tensile capacity (Clause 9.3.3)

Nominal tensile capacity is based on the bolt tensile stress area:

N_tf = A_s × f_uf

Design capacity: N_d,tf = phi_b × N_tf.

Utilization = N*_tf / N_d,tf ≤ 1.0

Combined shear and tension (Clause 9.3.4)

For bolts loaded simultaneously in shear and tension, the interaction is governed by the circular interaction formula:

Interaction ratio = (V*_f / V_d,f)^2 + (N*_tf / N_d,tf)^2 ≤ 1.0

Ply bearing capacity (Clause 9.3.2)

Bearing failure of the connected ply is checked through two mechanisms:

  • Ply tearing (edge failure): V_b,t = a_e × t_p × f_up
  • Ply bearing (interior): V_b,b = 3.2 × d_f × t_p × f_up

Design bearing capacity V_d,b = phi_p × min(V_b,t, V_b,b).

Utilization = V*_b / V_d,b ≤ 1.0

Serviceability friction checks (8.8/TF bolts)

For 8.8/TF friction bolts, the serviceability shear capacity is derived from the clamping force and slip factor:

V_d,sf = phi_b,f × V_sf

For combined serviceability shear and tension, the linear interaction formula applies:

Utilization = V*_sf / V_d,sf + N*_sf / N_d,sf ≤ 1.0

Capacity factors

  • phi_b = 0.8 (bolt connections)
  • phi_p = 0.9 (ply in bearing)
  • phi_b,f = 0.7 (friction bolt serviceability)

Related calculators

Steel Bolt→Steel Welds→Steel Welds→Steel Beam→

Frequently asked questions

What design code does this calculator use?
This calculator checks steel bolt connections to AS 4100:2020, Clause 9. It covers bolt shear and tensile capacity, ply bearing capacity, the combined shear-and-tension interaction check, and serviceability friction checks for high-strength bolts in the friction category.
What are the key inputs?
Key inputs are the bolt category and size, number of shear planes (threaded and unthreaded), ply thickness, ply tensile strength, edge distance on the controlling ply, and the applied design actions - shear, tension, in-plane moment, and out-of-plane moment on the bolt group. Friction bolt checks also require the slip factor and serviceability load factor.
What does the calculator output?
Outputs include the design shear capacity per bolt V_d,f, tensile capacity N_d,tf, ply bearing capacity V_d,b, and the combined shear-and-tension interaction ratio. For friction bolt configurations, the serviceability shear capacity V_d,sf and combined serviceability interaction ratio are also reported.
Can it handle bolt groups under combined shear and tension?
Yes. The calculator checks the circular interaction formula per AS 4100:2020 for bolts under simultaneous shear and tension: (V/V_d,f)^2 + (N/N_d,tf)^2 ≤ 1.0. The interaction ratio is the governing utilization for combined loading.
What bolt categories and sizes are supported?
The calculator supports the bolt categories defined in AS 4100:2020 - including 4.6/S, 8.8/S, 8.8/TB, and 8.8/TF categories - across standard metric bolt diameters. Bolt positions are entered as a table of X and Y coordinates, so any bolt group geometry is supported without restriction on the number of bolts.

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