Optimal design of seismic resistant planar steel frames

Seismic-resistant design of planar rectangular braced or unbraced steel frames is discussed. Nonlinear step by step integration is used as the analysis technique within the design process itself. The method directly quantifies the accepted seismic-resistant design philosophy that a structure: (1) resists moderate ground motion without structural damage, and (2) resists severe ground motion without collapse. Actual ground motion accelerograms are selected and scaled to levels representing moderate and severe ground motions. Constraints quantifying structural damage and limited nonstructural damage are constructed for the case of moderate ground motion. Constraints quantifying collapse and limited structural damage are constructed for the case of severe ground motion. In addition there are serviceability constraints on structural behavior under gravity loads only. Possible objective functions range from the minimization of structural volume to the minimization of response quantities such as story drifts or inelastically dissipated energy. Sophisticated optimization algorithms are utilized to solve the resulting mathematical programming problem.