Impact of Foundation Modeling on the Accuracy of Response History Analysis of A Tall Building

by Farzad Naeim, Salih Tileylioglu, Arzhang Alimoradi and Jonathan P. Stewart

Farzad Naeim, Salih Tileylioglu, Arzhang Alimoradi, Jonathan P. Stewart (2008). Impact of Foundation Modeling on the Accuracy of Response History Analysis of A Tall Building. SMIP08 Seminar on Utilization of Strong-Motion Data, p. 19 - 56.

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Soil-structure interaction can affect the response of buildings with subterranean levels by modifying the characteristics of input motions relative to those in the free-field and through the added system compliance associated with relative foundation/free-field translation and rocking. While procedures are available to account for these effects, they are seldom utilized in engineering practice. Our objective is to examine the importance of these effects on the seismic response of a 54 story building with four subterranean levels. We first generate a “most accurate” (MA) model that accounts for kinematic interaction effects on input motions, depth-variable ground motions along basement walls, compliant structural foundation elements, and soil flexibility and damping associated with translational and rocking foundation deformation modes. With reasonable tuning of superstructure damping, the MA model accurately reproduces the observed response to the 1994 Northridge earthquake. We then remove selected components of the MA model one-by-one to test their impact on building response. Factors found to generally have a modest effect on building response above ground level include compliance of structural foundation elements, kinematic interaction effects (on translation or rocking), and depth-variable ground motions applied to the ends of horizontal soil springs/dashpots. Properly accounting for foundation/soil deformations does not significantly affect vibration periods for this tall building (which is expected), but does impact significantly the distribution of inter-story drifts over the height of the structure. Two approximations commonly used in practice are shown to provide poor results: (1) fixing the structure at ground line with input consisting of free-field translation and (2) modeling subterranean soil layers using a series of horizontal springs which are fixed at their far ends and subjected to free-field ground accelerations.