Seismic Behavior of Multistory Braced Steel Frames

A step-by-step numerical procedure is used to compute the inelastic response of single-bay braced and unbraced steel frame structures. The dynamic response is computed by assuming an elasto-plastic type hysteresis behavior in tension only for the diagonal bracing members, in bending for the girders, and in bending with axial force effect on the plastic moment and the P-Δ effect included for the columns. The N-S component of the 1940 El Centro earthquake with the accelerations multiplied by 1.5 is used. The responses of several 10-story frames having varying arrangements of bracing members are proportioned by two different design philosophies. The first series is designed by using current code procedures, and the second series is a class of period-controlled structures. The results indicate that even light diagonal bracing members can significantly reduce lateral displacement and inelastic activity in the columns and girders. The axial force in the columns and floor accelerations can be substantially increased.