Seismic Response Predictions From 3D Steel Braced Frame Building Simulations

The seismic performance of steel building systems can be assessed through material and geometric nonlinear dynamic analysis. Extensive efforts have been conducted in the past, employing 2D building models, and incremental dynamic analysis to predict the collapse probability of steel building systems to earthquake excitation and justify seismic response modification coefficients (e.g., R) employed in equivalent lateral force-based design procedures. Little work has been performed on 3D building models where the vertical lateral force resisting system (LFRS) may interact with the building diaphragm. Here we examine two common steel braced frame vertical LFRSs: buckling restrained braces (BRBs) with their quite high R value, and concentrically braced frames (CBFs) with a more modest R. These systems are coupled with a variety of alternative composite steel deck floor and bare steel deck roof designs in a series of 3D building simlations of 1, 4, 8, and 12 stories in height. The building layout is regular, but with a relatively high aspect ratio to place increased demands on the diaphragm. The models indicate the expected degree of 3D interaction between the vertical LFRS and the diaphragm, and provide a means to understand the degree of conservatism inherent in existing and proposed diaphragm design methods. The role of P-Delta demands in the large deflection response of the buildings is highlighted.

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