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Australia
AS 4100:2020AS 4100:1998

Steel Bolt (old AS 4100:1998)

Structural engineers in Australia maintaining designs to AS 4100:1998 who need to check bolted connections under shear, tension, and combined loading. Suitable for projects where the earlier standard applies.

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What it calculates

Design and analyse bolt groups under shear, tension, and combined loading to AS 4100:1998. The elastic method distributes applied forces across the bolt group and checks shear, tensile, bearing, and friction limit states for the critical bolt.

Code standards

  • AS 4100:1998

How it calculates

The Steel Bolt (AS 4100:1998) calculator uses the elastic method to distribute applied loads across the bolt group and then checks each bolt and the governing ply against the strength and serviceability limit states in AS 4100 Clause 9.

Load distribution

Applied forces (design shear V*, tensile force 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 calculated assuming uniform bolt area across all positions.

For in-plane shear and moment, the elastic method distributes load to each bolt in proportion to its distance from the centroid using the polar moment of inertia I_z:

  • Direct shear per bolt = V* / n
  • Torsional shear due to moment = M_z × r / I_z (where r is the distance of the bolt from the centroid)
  • The horizontal and vertical components of torsional shear are resolved by the x and y coordinates of each bolt relative to the centroid

The critical bolt is the one with the highest resultant force from the vector sum of direct and torsional components.

Bolt shear capacity (Clause 9.3.2)

The nominal shear capacity V_f per shear plane depends on the bolt tensile stress area and the location of the shear plane relative to the threads:

  • Threaded shear plane: V_f = 0.62 × f_uf × A_s
  • Unthreaded shear plane: V_f = 0.62 × f_uf × A_o

The design shear capacity is 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 N_tf = A_s × f_uf, giving design tensile capacity N_d,tf = phi_b × N_tf.

Utilization = N*_tf / N_d,tf ≤ 1.0

Combined shear and tension interaction (Clause 9.3.4)

For bolts loaded simultaneously in shear and tension, the circular interaction check is:

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 in the connected ply is checked through two mechanisms:

  • Ply tearing (near edge): V_b,t = a_e × t_p × f_up
  • Ply bearing (away from edge): V_b,b = 3.2 × d_f × t_p × f_up

The governing nominal bearing capacity is the lesser of the two, and design capacity V_d,b = phi_p × V_b.

Utilization = V*_b / V_d,b ≤ 1.0

Serviceability friction checks (Clause 9.3.3 - friction bolts)

For high-strength bolts used in friction (8.8/TF category), the serviceability shear capacity accounts for clamping force and slip factor:

V_d,sf = phi_b,f × V_sf

The combined serviceability interaction for friction bolts under simultaneous shear and tension uses a linear interaction formula per the standard.

Utilization = V*_sf / V_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 4100:1998 (R2016). It covers bolt shear and tensile capacity, ply bearing, combined shear-and-tension interaction, and serviceability friction checks per Clause 9 of the standard.
What are the key inputs?
Key inputs include the bolt category and size, number of shear planes with and without threads, ply thickness and tensile strength, applied design shear force, tensile force, in-plane moment, and out-of-plane moment on the bolt group. Serviceability inputs cover the slip factor and serviceability load factor for friction bolt checks.
What does the calculator output?
Outputs include the design shear capacity per bolt (V_d,f), tensile capacity (N_d,tf), bearing capacity on the controlling ply (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. For bolt groups with simultaneous shear and tension, the calculator evaluates the interaction ratio using the circular interaction formula: (V/V_d,f)^2 + (N/N_d,tf)^2 ≤ 1.0. The result is shown as a utilization ratio - values at or below 1.0 indicate a satisfactory design.
What bolt categories and sizes are supported?
The calculator supports the bolt categories defined in AS 4100:1998 - including 4.6/S, 8.8/S, 8.8/TB, and 8.8/TF categories - across standard metric bolt sizes. Bolt geometry (x and y coordinates) is entered as a table, so arbitrary group layouts are supported without restriction on the number of bolts.

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