ABSTRACT
Three-dimensional non-linear dynamic time-history analyses of a three-story steel moment-resisting frame designed according to the Uniform Building Code for Los Angeles seismicity were carried out. Beams in both directions had moment connections to the hollow rectangular columns. Analyses were performed with design level ground motions applied at different angles to the structure. It was found that code drift limits, rather than code considerations for bi-directional horizontal shaking, governed the member sizes. The structure exceeded its yield drift in both directions simultaneously. Significant column yielding at levels above the base occurred because the columns were not required to be designed for the plastic flexural strength of the beams in both directions simultaneously. Orthogonal shaking increased drifts by 46%. Two dimensional analyses may therefore be non-conservative in estimating the behavior of this type of 3-D structure.
