Nonlinear Responses of High-Rise Buildings in Giant Subduction Earthquakes

Abstract

With the exception of the 2003 Tokachi-Oki earthquake, strong ground recordings from large subduction earthquakes (Mw > 8.0) are meager. Furthermore there are no strong motion recordings of giant earthquakes. However, there is a growing set of high-quality broadband teleseismic recordings of large and giant earthquakes. In this thesis, we use recordings from the 2003 Tokachi-Oki (Mw 8.3) earthquake as empirical Green’s functions to simulate the rock and soil ground motions from the 2004 Sumatra-Andaman earthquake and a scenario Mw 9.2 Cascadia subduction earthquake in the frequency band of interest to flexible and tall buildings (0.075 to 1 Hz). The effect of amplification by the Seattle basin is considered by using a basin response transfer function, which is derived from deconvolving the teleseismic waves recorded at rock sites from basin sites at the SHIP02 experiment. These strong ground motion time histories are used to simulate of the fully nonlinear response of 20-story and 6-story steel moment-frame buildings designed according to both the U.S. 1994 Uniform Building Code and the 1987 Japanese building code. We consider several realizations of the hypothetical subduction earthquake. The basin amplification and the down-dip limit of rupture are of particular importance to the simulated ground motions in Seattle. At rock sites, if slip is limited to offshore regions, the building model responses are mostly in the linear range. However, if rupture is extended beyond the Olympic Mountains, large deformations occur in the high-rise buildings models, especially those with brittle welds. At basin sites, our simulations indicate the collapse of all building models for a source model with rupture beyond the Olympic Mountains, whereas buildings with perfect welds avoid collapse for simulations based on a source model with rupture limited to offshore. The synthetic ground motions all have very long durations (more than 5 minutes at soil sites), and our building simulations should be considered as a low estimate since we the degradation model used in our simulation did not consider local flange buckling.