Australian & New Zealand Design Parameters

Parameters controlling the steel design are entered on the Member Design Parameters spreadsheet. These parameters are entered on a per member basis, and control the code checking on a per member basis.

Alpha_m Factor

(Moment Modification Factor)

• If this entry is left blank, RISA calculates it based on the full length of the member.

• When unbraced lengths (Lb_comp_top and Lb_comp_bot) are explicitly defined (enter a number), the program does not have the segmental information of the member for alpha_m calculation.

  It assumes the alpha_ m used for this particular member to be 1.0.

• When unbraced lengths (Lb_comp_top and Lb_comp_bot) are defined by physical nodes along the member with the entry ‘Segment’ typed in, alpha_m is calculated automatically using equation 5.6.1.1(2) based on segments defined by nodes along the member.

The alpha_m value is influenced by the sway condition of the member and is dependent on the member's end moments, which changes from one Load Combination to the next.

Australian & New Zealand Limitations

Tapered Members - Tapered WF shapes are done per the AISC LRFD 3rd specification at this time. The appropriate sections of the ENV 1993-1-1 specification are used in a later release.

Torsional Warping Effects- Combined bending and warping torsional stresses in WF and Channel shapes are handled per the AISC publication "Torsional Analysis of Steel Members".

WT and Double Angle Limitations - The NZ / AS codes do not address the rare case where Lateral Torsional (or Flexural Torsional) Buckling occurs for WT's and double angles bent about their weak axis.

Torsional Unbraced Length - At present the program assumes 'Lcomp' as 'Le' in case of lateral torsional buckling. Section 5.6.3 provides a procedure for calculating 'Le' which is not being addressed at this time.

Special Provisions for Cantilevers - At present the program does not address section 5.6.2 for cantilever elements.