Effect of Shaking Characteristics on Steel Moment-Resisting Frames

Inelastic dynamic time-history analyses of nine steel frames were performed to understand effect of ground motion characteristic on structural response. Particular ground motion characteristics studied were the effect of near-fault ground shaking, soft-soil shaking and vertical shaking. Record frequency content and magnitude effects were also investigated. It was found that near-fault strike-normal records caused demands as high as 6.7%, residual displacements were approximately 52% of the peak inelastic displacements, and the SRSS method for predicting the maximum increase in column axial force for simultaneous vertical and horizontal shaking was non-conservative due to frame inelasticity. Soft-soil records increased displacements of a 3 story frame by up to 56% above those from design level motions. Drifts did not increase linearly with increasing earthquake ground acceleration and showed significant variation depending on the earthquake record. Changing the record frequency content while maintaining the spectral response at the fundamental period of the structure affected the story in which peak drift demand occurred.