AS 4100 solver


The aim has generally been to use the highest tier equations, with all calculations performed exactly in accordance with AS 4100.

BCDsteel has been verified where possible by comparison with published data and commercially available software. Many aspects such as slender section capacity, the equal angle solvers, flexural torsional buckling of struts, and tapered member capacity have had to be verified against data generated independently in Excel.


Rotational restraints (Clause and lateral restraints (Clause are intentionally not included to simplify input. This means that sub-segments (Clause are not included in the analysis. This is conservative, but can penalise the design of some members such as the rafters of portal frames.

Section capacity

For bending of slender sections, the effective section modulus Ze is calculated using the effective cross-section that is determined by omitting the ineffective width from each flat element that is fully or partly in compression.

For bending about a principal axis, there are 2 values of section capacity øMs corresponding to compression first on 1 side of the neutral axis and then on the other. For a section that is symmetrical about an axis, the 2 values are identical. For a section that is unsymmetrical about an axis and for which the 2 capacities are not identical, BCDsteel uses the lower value. This is conservative. However, it does penalise T-sections in particular. Other sections that may be affected include unequal flange I-sections, channels and angles.

The section capacity is calculated at 9 equi-spaced locations along the length of each member. The Utilisation Ratio is calculated at each of these sections for each design criteria. The value reported for each criteria is the maximum value at all locations along the member.

BCDsteel does not take into account any reduction in capacity due to bolt holes at connections. This must be assessed by the user as part of the connection design – not included in BCDsteel.

Member capacity

For bending about the major x-axis, the member capacity is calculated for each segment along a member in accordance with Clause, AS 4100. The ratio M*x/øMbx is calculated for each segment using the maximum value of M*x along that segment. The Utilisation Ratio for the member is the maximum value of M*x/øMbx for all segments along the member.

Star equal angles defined in the model using a mirror option will be automatically identified and analysed in accordance with Clause 6.4.3 for compression and Clause 7.2 for tension. The number of intermediate battens is defined in the Settings tab.

Angle web bracing members may be analysed to Clause 8.4.6 for compression and Clause 7.2 for tension. Clause 8.4.6 typically gives much higher capacity than Clause 8.4.5. As a guide, some tests gave 1.17 to 1.65 times higher capacity for L/r = 75 to 150.

Members may be stepped or tapered along their length. The program analyses them in accordance with the rules in AS 4100. For I-sections and channels that have equal flanges, and for which the major axis is parallel to the flanges, the member capacity for bending about the major axis øMbx is calculated in accordance with Clause using the properties of the cross-section at the critical section as defined in Clause 5.3.3. The axial compression flexural buckling capacity of the member øNcx and øNcy are calculated using the minimum value of øNs along the member in accordance with Cl 6.3.4(a).