D9.A.5 Column Design

Columns are designed for axial force, MZ moment, MY moment, and shear force. Both the ends of the members are designed for all the load cases and the loading which produces largest amount of reinforcement is called as critical load. If Track 0 or Track 1 is used, design results will be printed for critical load only. But if Track 2 is used, you can get detailed design results of that member. The value of Pt needed for minimum axial force, maximum axial force, maximum MZ, maximum MY among all the load cases for both the ends will be printed. If the MMAG parameter is used, the column moments will be multiplied by that value. If the SMAG parameter is used, column shear force will be multiplied by that value.

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 ´ (ratio-0.2), 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.

D9.A.5.1 Example

UNIT KGS CMS
START CONCRETE DESIGN
CODE JAPAN
FYMAIN SRR295 ALL
FC 210 ALL
CLEAR 2.5 MEMB 2 TO 6
DESIGN COLUMN 2 TO 6
END CONCRETE DESIGN