For calculating member slenderness, the length of unbraced segment for compression is considered.

For analytical member design, the MAIN and TMAIN parameters are used.

Bending capacities are calculated per NZS3404 Section 5. The allowable bending moment of members is determined as the lesser of nominal section capacity and nominal member capacity (ref. Cl.5.1).

Section web shear capacity, φV_v , is calculated per Cl.5.11, including both shear yield and shear buckling capacities. Once the capacity is obtained, the ratio of the shear force acting on the cross section to the shear capacity of the section is calculated. If any of the ratios (for both local Y & Z-axes) exceed 1.0 or the allowable value provided using the RATIO parameter, the section is considered to have failed under shear.

The following table highlights which shear capacities are calculated for different profile types.

Only unstiffened web capacities are calculated. Stiffened webs are not considered. Bearing capacities are not considered.

The TSP design parameter is used in shear capacity calculations.

The compressive strength of members is based on limit states per NZS3404 Section 6. It is taken as the lesser of nominal section capacity and nominal member capacity.

The criteria governing the capacity of tension members are based on two limit states per NZS3404 Section 7.

The limit state of yielding of the gross section is intended to prevent excessive elongation of the member.

The second limit state involves fracture at the section with the minimum effective net area φN_t section axial tension capacities are calculated (Cl.7.2). Through the use of the NSF parameter, you may specify the net section area. STAAD.Pro calculates the tension capacity of a member based on these two limit states per Cl.7.1 and Cl.7.2 respectively of NSZ3404. Eccentric end connections can be taken into account using the KT correction factor, per Cl.7.3. The f_y yield stress is based on the minimum plate yield stress. Parameters FYLD, FU, and NSF are applicable for these calculations.

STAAD.Pro does not design sections or members for torsion for NZS3404.

The program performs the following checks per the seismic provisions in section 12 of the code.

1. Minimum specified yield stress (table 12.4)
2. Maximum ratio of (fy / fu) (table 12.4)

   The member seismic category is specified using the DUCT design parameter.

3. Fabrication requirement (Sec.12.4.1.2) - Category 1 or 2 members shall be hot-rolled or fabricated by welding from hot-rolled plate, except that category 2 members may be cold-formed, provided that adequate ductility capacity of the member and its connections is established by experimental testing or rational design.
4. Element slenderness (sec.12.5.1.1) - The elements of category 1, 2, 3 and 4 shall comply with the plate-element slenderness limitations presented in Table 12.5.
5. Section symmetry requirement (sec.12.5.2) – The yielding regions of category 1 or 2 members shall be doubly symmetric sections. The yielding regions of category 3 members shall be doubly or singly symmetric sections.
6. Web slenderness of beam (sec.12.7.2.1) - The web thickness within the yielding region of a beam shall be not less than (d1/82) (fy / 250) for a category 1 or 2 member or less than (d1/101) (fy / 250) for a category 3 member.
7. Limit on axial force (sec.12.8.3.1) - The ratio of design axial force, N*, to design section capacity, ϕN_s , (refer to 6.2) shall not exceed the values given in (a) through (c) below:
   1. The general limit given in table 12.8.1.
   2. In addition to (a), for category 1, 2 and 3 column members, excluding brace members of concentrically and eccentrically braced frames, the following limitation on design axial compression shall apply, unless waived according to 12.8.3.2

      $N^{*}\le \varphi N_s\left(\frac{1+{\beta }_m-\sqrt{N_s/N_{oL}}}{1+{\beta }_m+\sqrt{N_s/N_{oL}}}\right)$

      Eq. 12.8.3.1

   3. When the slenderness ratio for the member web exceeds that given in table 12.8.2 for the appropriate member category, the design axial force generated by gravity loading alone, Ng*, shall comply with the axial force limitation equation given therein.
8. Shear-bending interaction (12.10.3.1) - When a capacity design procedure is not used, at yielding regions in category 1 or 2 beams forming part of a seismic-resisting system, when designing for load combinations including earthquake loads the nominal web shear capacity of the beams shall be taken as 80% of that calculated from 5.11.4.1 and the interaction of shear and bending moment shall satisfy:

   M* ≤ ϕMsv

   where

   Msv

   =

   $\begin{array}{cc}{M}_s& \text{for }{V}^{*}\le 0.6\varphi V_w\\ M_s(1.38-\frac{V^{*}}{1.6V_w})& \text{for }0.6\varphi V_w\le V^{*}\le 0.8\varphi V_w\end{array}$

   The ratio will be calculated as – M* / ϕM_sv