Structures often exhibit nonlinear and inelastic behavior in the form of hysteresis loop under severe loads associated with earthquake, austere winds and waves. Hysteresis is particularly important in depicting the nonlinear response of wood buildings, braced steel frames, reinforced concrete, and structures with a high proportion of composite materials. A practical model of hysteresis that would match experimental observations on real structures is needed for the successful design of structures against earthquakes and strong winds. Two different time-domain system identification algorithms will be presented in this report to estimate the parameters of an extended Bouc-Wen hysteretic model. This version of the differential model of hysteresis can curve-fit practically any hysteresis trace with a suitable choice of the model parameters. Thirteen control parameters are included in the model. The parameter identification algorithms presented in this report include the constrained simplex and generalized reduced gradient methods. Noise filtering techniques and constraints will also be used in this study to assist in parameter identification. The effectiveness of the proposed algorithms will be demonstrated through simulations of nonlinear systems with pinching and degradation characteristics. Due to very modest computing requirements, the proposed identification algorithms can be acceptable as a basic tool for estimating hysteretic parameters in engineering design.

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