AS 4100 Bolt Group Design Guide

A practical workflow for bolt group verification under AS 4100 without reproducing copyrighted code text or proprietary table values.

This article walks through the steps you should follow when designing or checking a bolted connection to AS 4100:2020. It is intended to help you:

define actions and connection geometry clearly,
identify governing limit states for bolted connections,
keep capacity reduction factors and load combinations explicit, and
cross-check calculator outputs against independent reasoning.

This is a workflow guide. It does not reproduce AS 4100 clause text or table values and does not provide project-specific design criteria.

Copyright and standards notice

Steel design standards and building codes are typically copyrighted by their publishers and may be sold as paid documents. This site does not reproduce copyrighted code clauses or proprietary tables. Any discussion of standards on this page is high-level, non-exhaustive, and intended to help users understand terminology and organize verification workflows. Always consult the official published standard (AS 4100:2020 and any referenced companion standards) for authoritative requirements.

1) Start with a clean problem statement

Before touching a calculator, record the information that defines the problem:

the design actions at the connection interface (axial force, shear, moment, and their combinations),
the connection geometry (number of bolts, gauge, pitch, edge distances, plate dimensions),
the bolt specification (grade, type, and installation category such as 8.8/S, 8.8/TB, or 8.8/TF),
the connected plate or member material grade and thickness, and
any detailing constraints (access for tensioning, clearances, coating systems).

Many "mystery" discrepancies happen because two checks are actually checking different problems.

2) Identify the limit state families

Bolted connections under AS 4100 are checked against multiple limit states. Depending on the connection configuration, relevant families typically include:

bolt shear capacity (single or double shear, threads included or excluded from the shear plane),
bolt tension capacity and combined tension-shear interaction,
ply bearing capacity at each bolt location,
plate tear-out along the bolt line,
block shear (tearing) of the connected element along combined shear and tension paths, and
net section capacity of the connected member.

Slip-critical connections (8.8/TF category) add a serviceability-level slip resistance check. List every candidate family explicitly, then confirm which ones govern for your particular geometry and loading.

3) Keep factors and combinations explicit

AS 4100 uses capacity reduction factors (phi) that vary by failure mode, and the loads are factored per AS/NZS 1170 combinations. When documenting a check:

record whether actions are characteristic, factored, or serviceability values,
record the capacity reduction factor used for each limit state,
confirm that you are comparing factored actions against design capacities (not mixing unfactored demands with reduced capacities), and
note which load combination governs and why.

This is not about memorizing factor values. It is about making the factor structure auditable so a reviewer can trace every number.

4) Use tools as arithmetic engines, not as authorities

A web calculator is most valuable when you already know:

which limit state you are evaluating,
what each input represents, and
which standard and bolt category you are working with.

Use the calculators on this site to:

compute individual bolt and connection capacities quickly,
compare alternative bolt layouts and plate thicknesses, and
produce a structured output that feeds into your calculation note.

Then validate the controlling limit state independently with a simplified hand check or a second tool.

5) Worked-example structure (template, not values)

A defensible calculation note for a bolted connection typically follows this structure:

Given: design actions (N*, V*, M*), connection geometry, bolt specification (e.g., M20 8.8/S), plate grade, and member section.
Assumptions: hole type (standard, oversize, slotted), thread condition at shear plane, number of shear planes, prying action consideration, and any simplifications.
Checks: compute capacity for each relevant limit state (bolt shear, bearing, tear-out, block shear, net section) and report utilization ratios.
Controlling mode: identify the limit state with the highest utilization ratio as the governing check.
Sensitivity: show how changing one parameter (e.g., adding a bolt row, increasing plate thickness, or switching from snug-tight to tensioned bolts) shifts the utilization.
Conclusion: summarize whether the connection is likely adequate subject to full code compliance verification and professional review.

This template is reusable across projects even when the numeric details change entirely.

6) Common mistakes to avoid (AS 4100-flavored)

Confusing 8.8/S (snug-tight, bearing-type) with 8.8/TB (fully tensioned, bearing-type) or 8.8/TF (friction-type). The installation category changes both the capacity model and the required inspection.
Using standard-hole capacity for oversize or slotted holes without adjusting the effective area.
Ignoring prying action in connections with flexible flanges or end plates loaded in tension.
Using gross area where net area is required, or vice versa. AS 4100 has specific rules about which area applies to each limit state.
Reporting a single utilization ratio without listing all evaluated limit states. A reviewer needs to see that you checked the full set of failure modes.
Assuming that bolt shear always governs. Bearing, tear-out, or block shear often control in thin-ply or short-edge-distance configurations.

These are workflow and judgment mistakes, not arithmetic mistakes.

FAQ

Is this article a substitute for AS 4100? No. It is a workflow guide that avoids reproducing copyrighted text. Consult the published standard (AS 4100:2020) for authoritative rules and clause requirements.

What is the difference between 8.8/S, 8.8/TB, and 8.8/TF bolt categories? These categories describe different installation and design assumptions. The distinction affects whether the connection relies on bolt bearing, bolt tension, or friction. Consult AS 4100 for the precise definitions and when each category is required.

Does the calculator check every AS 4100 bolt limit state? No. The calculator supports common screening checks for typical bolted connection configurations. Unusual geometries, fatigue loading, and special detailing may require more detailed analysis.

How do I handle prying action? Prying occurs when flexible connection elements amplify bolt tension beyond the applied load. The workflow is to first check whether prying is significant, then adjust bolt tension demands accordingly.

Can I use this workflow for connections to hollow sections? The general structure applies, but hollow sections introduce additional failure modes (chord face yielding, punching shear) not covered here.

Why should I document the controlling limit state? Because it turns a calculator output into an engineering judgment. Without it, a reviewer cannot assess margin adequacy.

What if my bolt group has both shear and tension? Combined loading requires an interaction check. Compute individual utilizations, then check combined interaction per AS 4100.

Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice, a design service, or a substitute for an independent review by a qualified structural engineer. Any calculations, outputs, examples, and workflows discussed here are simplified descriptions intended to support understanding and preliminary estimation.

All real-world structural design depends on project-specific factors (loads, combinations, stability, detailing, fabrication, erection, tolerances, site conditions, and the governing standard and project specification). You are responsible for verifying inputs, validating results with an independent method, checking constructability and code compliance, and obtaining professional sign-off where required.

The site operator provides the content "as is" and "as available" without warranties of any kind. To the maximum extent permitted by law, the operator disclaims liability for any loss or damage arising from the use of, or reliance on, this page or any linked tools.