D9.A.5 Column Design
Column design is done for Rectangular, Square and Circular sections. For rectangular and square sections Pt value is calculated separately for MZ and MY, while for circular sections Pg value is calculated for MZ and MY separately.
Column design for biaxial moments is optional. If the BIAXIAL parameter value is 1.0, the program will design the column for biaxial moments. Otherwise column design is always uniaxial.
Steps involved:

Depending on the axial force zone is determined for Pt = 0.0 .

If the column is in "zone A", design is performed by increasing Pt and checking allowable load for that known Pt and known actual eccentricity of the column.

If the column is in "zone B" or in "zone C", xn is calculated for given P and Pt and checking is done for allowable moment, if allowable moment is less than the actual moment, program increases Pt and this procedure continues until the column design conditions are satisfied or the column fails as the required Pt is higher than Pt maximum value.

If the column is in tension, design is done by considering allowable tensile stress of steel only.

If biaxial design is requested program solve the following interaction equation

where, a = 1.0+1.66666666 ´ (ratio0.2), ratio = P/Pcap & 1.0 £ a £ 2.0, Mycap, Mzcap & Pcap represents section capacity

If the interaction equation is not satisfied program increases Pt and calculates Pcap, Mycap and Mzcap and solve the interaction equation again and this process continues until the eqn. is satisfied or the column fails as Pt exceeds its maximum limit.

If biaxial design is not requested program assumes that interaction equation is satisfied (if uniaxial design is performed successfully).

If the interaction equation is satisfied program determines bar size and calculates no. of bars and details output is written.