General Applicability of a Nonlinear Model of a One Story Steel Frame

摘要

This report deals with the question of whether a nonlinear mathematical model of a structure constructed using system identification and the nonlinear structural response to one particular earthquake excitation, can satisfactorily predict the nonlinear responses of the same structure to other earthquake excitations. The structure is a single story steel frame, and the study consists of both experimental and analytical parts. The physical structure is subjected to four historical strong motion earthquake acceleration time histories by means of the shaking table at the Earthquake Engineering Research Center of the University of California, Berkeley, California. The analytical part consists of constructing a mathematical model of the structure. The form of the model is the same as that adopted by Matzen and McNiven. It accommodates viscous damping and nonlinear material behavior by means of the Ramberg-Osgood equations. The parameters in the model (there are four) are established from the responses to the El Centro earthquake. With the mathematical model complete, responses to the El Centro, Pacoima, Taft and Parkfield Earthquakes are predicted using the model. These responses are compared to the corresponding responses from the experimental program. The significant finding from the study is that the mathematical model, constructed using response data from the El Centro earthquake, predicts responses to the other three earthquakes as accurately as it does to the El Centro. The shortcoming of the model, equally evident in its prediction of all four earthquakes, is its inability to predict displacement time histories, following the first major excursion into the plastic deformation domain. The authors indulge in the luxury of accounting for the weakness and suggest ways for overcoming it, with the price attached.