Steel Checks to AS 4100

The steel design check supports the AS 4100-1998 version

Input data

All cases provided to the checker are assumed to be ultimate limit state (i.e. the member forces are fully factored). Any non ULS cases – e.g. unfactored wind load – will be treated as if they are ULS, and so will result in non-conservative utilizations.

Effective Section Properties

Members subjected to bending are classified as Compact, Non-compact and Slender sections in accordance with AS4100:1998 clause 5.2 and Table 5.2. The effective section modulus is computed using the appropriate clause from AS4100:1998 5.2.3, 5.2.4 and 5.2.5.

Members subjected to axial compression are classified as Compact, Non-compact and Slender sections in accordance with AS4100:1998 clause 6.2.3

Local Checks

Sections are checked at the ends of every sub-span of the member for the moments and forces acting on it.

Shear

Shear is checked according to AS4100:1998 clause 5.11. While calculating the shear strength steel checker assumes that the section web is unstiffened.

The shear area is calculated based on clear web depth between flanges for the welded sections, and based on full web depth for rolled section. For RHS and Box sections the shear area is based on two clear web depths.

Shear capacities are reduced to account for moment in the direction of shear force according to AS4100:1998 5.12.3

Bending moment

Moment capacity at a section is calculated in accordance AS4100:1998 clause 5.2.1. See Effective Section Properties for details on calculation of effective section modulus.

Axial Force

Compression capacity at a section is calculated in accordance with AS4100:1998 clause 6.2.1. See Effective Section Properties for details on calculation of effective area of section.

Tension capacity at a section is calculated in accordance with AS4100:1998 clause 7.2 and 7.3. Sections in tension use the user defined ‘Net Area Ratio’.

Torsion

At present, any significant torsional moment (greater than 5% of the torsional capacity) produces a warning.

Combined local effects

The section is checked against all the applied forces using the equations in AS4100:1998 clause 8.3.4. The choice of equations used depends on the section shape and the section’s local buckling class.

Moments used in the local interaction check include the moments due to eccentricity in axial force. Eccentricity may be due to end connection and to shift in neutral axis in case of Unsymmetrical slender sections.

Buckling Checks

Axial Buckling

The member is checked along its length for major axis axial buckling and minor axis axial buckling according to AS4100:1998 clause 6.3.3.

Unsymmetrical sections are also checked for torsional and flexural torsional buckling according to AS4100:1998 clause 6.3.3. Lambda value will be computed in accordance with clause 6.3.4.

At present the effective length of the member is calculated from the factors available in AS4100:1998 Figure 4.6.3.2.

Lateral Torsional Buckling

Members with full lateral restraint are checked for Lateral torsional buckling in according to AS4100:1998 clause 5.3. Lateral restraints are verified in accordance with AS4100:1998 clause 5.3.2.

Lateral torsional buckling is checked in accordance with AS4100:1998 clause 5.6.1 and 5.6.2(i) for the member without continuous restraints. Effective lengths for lateral torsional buckling are calculated according to AS4100:1998 clause 5.6.3.

If the member has a Lateral Torsional Buckling Factor override, this is used in place of AlphaM.

Buckling Interaction

Interaction checks are carried out according to AS4100:1998 clause 8.4.5.1 and 8.4.5.2 for compression and tension members respectively. Reduced moments used in compression member checks are calculated using the simplified equations in AS4100:1998 clause 8.4.2.2 and 8.4.4.1.