Fully Nonlinear versus Equivalent Linear Computation Method for Seismic Analysis of Midrise Buildings on Soft Soils

In this study, the accuracy of a fully nonlinear method against an equivalent linear method for dynamic analysis of soil-structure interaction is investigated comparing the predicted results of both numerical procedures. Three structural models, including 5-story, 10-story, and 15-story buildings, are simulated in conjunction with two soil types with shear-wave velocities less than 600 m/s. The aforementioned frames were analyzed under three different conditions: (1) fixed-base model performing conventional time history dynamic analysis under the influence of earthquake records, (2) flexible-base model (considering full soil-structure interaction) conducting equivalent linear dynamic analysis of soil-structure interaction under seismic loads, and (3) flexible-base model performing fully nonlinear dynamic analysis of soil-structure interaction under the influence of earthquake records. The results of these three cases in terms of average lateral story deflections and interstory drifts are determined, compared, and discussed. It is concluded that the equivalent linear method of the dynamic analysis underestimates the inelastic seismic response of midrise moment resisting building frames resting on soft soils in comparison with the fully nonlinear dynamic analysis method. Therefore, a design procedure using the equivalent linear method cannot adequately guarantee the structural safety for midrise building frames resting on soft soils. (C) 2014 American Society of Civil Engineers.