Challenges in Specifying Ground Motions for Design of Tall Buildings in High Seismic Regions of the United States

Abstract eng:
Many tall buildings in high seismic regions of the United States are being designed using performance-based earthquake engineering principles under alternative design provisions allowed in the current building code. Still-evolving design criteria for tall buildings generally require that these buildings be designed for collapse prevention under a very rare earthquake (with a long recurrence interval, on the order of 2,475 years). Alternative design criteria for tall buildings generally specify some deviations from prescriptive building code provisions, thus allowing for greater building heights, more use of high strength materials, and less structural redundancy among other things. However, because of the deviations from prescriptive provisions, nonlinear time history analysis is required. When using probabilistic seismic hazard analysis, the ground motions developed for very rare earthquakes are dominated by uncertainties. There is great difficulty in identifying or developing realistic strong ground motion time histories for these rare events. In addition, trying to account for source-to-site effects, such as basin, near-source, and directivity effects, becomes increasingly complex. Developing representative ground motion time histories may involve scaling or modification of actual time histories, in either the time or frequency domains, to match the target response spectrum. Alternatively, artificial time histories may be generated to match the target response spectrum. Advances in ground motion simulations of time histories for model events also hold some promise. There is a great challenge in specifying the ground motions for realistic analysis to result in safe and economical design of tall buildings in high seismic regions.

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