D7.A.5 Member Capacities

The allowable stresses used in the implementation are based on DIN 18800 (Part 1) - Section 7. The procedures of DIN 18800 Part 2 are used for stability analysis. The basic measure of member capacities are the allowable stresses on the member under various conditions of applied loading such as allowable tensile stress, allowable compressive stress etc. These depend on several factors such as cross sectional properties, slenderness factors, unsupported width to thickness ratios and so on. Explained here is the procedure adopted in STAAD for calculating such capacities.

D7.A.5.1 Checks for Axial Tension

In members with axial tension, the tensile load must not exceed the tension capacity of the member. The tension capacity of the member is calculated on the basis of the member area. STAAD calculates the tension capacity of a given member based on a user supplied net section factor (NSF -a default value of 1.0 is present but may be altered by changing the input value, see D7.A.7 Design Parameters) and proceeds with member selection or code checking.

D7.A.5.2 Checks for Axial Compression

The compression capacity for members in compression is determined according to the procedure of DIN 18800- Part 2. Compressive resistance is a function of the slenderness of the cross-section (Kl/r ratio) and the user may control the slenderness value by modifying parameters such as KY, LY, KZ and LZ.

D7.A.5.3 Checks for Bending and Shear

The bending compressive and tensile capacities are dependent on such factors as length of outstanding legs, thickness of flanges, unsupported length of the compression flange (UNL, defaults to member length) etc. Shear capacities are a function of web depth, web thickness etc. Users may use a value of 1.0 or 2.0 for the TRACK parameter to obtain a listing of the bending and shear capacities.