Steel Checks to HKSUOS

The steel design check supports the Hong Kong Code of Practice 2005 and 2011 editions.

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 are classified as Class 1, Class 2, Class 3 and Class 4 sections in accordance with HKSUOS:05 Table 7.1 and 7.2. The channel webs are classified according to BS5950-1:2000 Table 11 since HKSUOS:05 does not specify the same. Effective section properties are calculated according to the appropriate clause from HKSUOS:05 clause 11.3.4. For flanges with non-uniform compression the effective width of the plate is calculated according to EN 1993-1-5:2006 clause 4.4.

Effective Plastic Modulus

Class 3 semi-compact sections subjected to bending are designed using effective plastic modulus according HKSUOS:05 clause 7.5.

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 HKSUOS:05 clause 8.2.1. Shear is checked only if the section’s web(s) are not slender. A warning is given if the section is slender in shear.

Bending moment

Moment capacity at a section is calculated in accordance with HKSUOS:05 clause 8.2.2. See Effective Section Properties for details on calculation of effective section modulus.

Moments are conservatively enhanced if slenderness or end connection leads to the effective centroid of the section moving, and axial force is present.

Moment capacities are reduced to take account of high shear according to HKSUOS:05 clause 8.2.2.2 and compared with the applied moments.

Axial Force

Compression capacity at a section is calculated in accordance with HKSUOS:05 clause 8.9.1. See Effective Section Properties for details on calculation of effective area of section.

Tension capacity at a section is calculated in accordance with HKSUOS:05 clause 8.6. 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 for interaction of axial, shear and moments using the equations in HKSUOS:05 clause 8.9.1 and 8.2.1.

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

Buckling Checks

Axial Buckling

The member is checked along its length for major axis axial buckling and minor axis axial buckling according to HKSUOS:05 clause 8.7. Unsymmetrical sections are checked for torsional and flexural torsional buckling according to the HKSUOS:05 clause 8.10. At present the effective length of the member is calculated from the factors available in HKSUOS:05 Table 8.6 based on the restraints on the member; this value can be overridden from the steel design properties.

Torsional and Flexural-Torsion Buckling

Unsymmetrical sections are checked for torsional and flexural torsional buckling according to the HKSUOS:05 clause 8.10

Lateral Torsional Buckling

Lateral torsional buckling is checked in accordance with HKSUOS:05 clause 8.3, Appendix 8.1.and Appendix 8.2.

Appendix 8.2 provide guidance to calculate $λ_{Lt}$ for uniform I, H and channel with equal flanges. It also suggested to use recognized buckling analysis for other section shapes. Currently BS5950-1:2000 formulations are using to calculate $λ_{Lt}$ for RHS and T sections.

If a member has an Equivalent Uniform Moment Factor override specified, this is used in place of $m_{LT}$ for for lateral torsional buckling (HKSUOS:05 clause 8.3.5.2).

Buckling Interaction

Interaction checks are carried out according to HKSUOS:05 clause 8.9.2. Since it is assumed that the analysis results are inclusive of second order p - small delta analysis, the amplification factor is ignored for non-sway frame members.

If the member has Moment Amplification Factor overrides, these are used instead of the values calculated according to the code. The moment amplification factor is only applied to members with compression force no matter the moment amplification factor is calculated or override value.