steelBolt

Design and analyze 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.

This calculator uses an earlier code edition (AS4100:1998 (R2016)). It stays available for existing projects. For new designs, check the [Calculator Library](/docs/calculators/au) for the current edition. ## Method & scope | Property | Detail | | -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | What it checks | Load distribution, Bolt shear capacity (Clause 9.3.2), Bolt tensile capacity (Clause 9.3.3), Combined shear and tension interaction (Clause 9.3.4), Ply bearing capacity (Clause 9.3.2), Serviceability friction checks (Clause 9.3.3, friction bolts), Capacity factors | #### Calculation method 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) ## How to use it Open it from **Run calc** in the About this calculator panel above. Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See [Checks, References, Conditions and Assumptions](/docs/running-calculations/checking-results/checks-references-conditions-assumptions). Check the utilization of each governing check in the summary, then export a PDF report. See [Views and Export](/docs/running-calculations/exporting-reports/views-and-export). ## Common questions 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. 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. 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. 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. 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. ## Next steps Complete list of Calcs.com design calculators available for Australian and New Zealand projects (AS 3600, AS 4100, AS 1720, AS/NZS 1170, and related standards). Design and analyze steel bolt connections to AS 4100:2020. Supports arbitrary bolt layouts with shear, tension, bearing, and friction serviceability checks. Analyze and design weld connections to AS 4100:2020, Cl 9.6. Checks fillet weld and butt weld capacity under combined shear and tension force per unit length. Design fillet and butt weld connections to AS 4100:1998 (R2016). An earlier code edition, kept for existing projects. Design steel beams to AS 4100:2020 with multiple supports and loads. Floor- and roof-beam presets cut repetitive entry.