IDENTIFICATION OF HYSTERETIC OSCILLATORS UNDER EARTHQUAKE LOADING BY NONPARAMETRIC MODELS

Nonparametric identification techniques are used to process recorded d ata of nonlinear structural responses and to represent the constitutiv e relationship of the structure. When hysteretic systems are dealt wit h, attention must be given to the appropriate subspace of the state va riables in which the restoring force can be approximated by a single-v alued surface. Nonparametric models are investigated, defined by two d ifferent descriptions: the first, in which the restoring force is a fu nction of displacement and velocity, is commonly used; and the second, in which the incremental force is a function of force and velocity is less adopted. The ability of the second variable space to better repr oduce the behavior of hysteretic oscillators is shown by analyzing dif ferent cases. Meanwhile, approximation of the real restoring function in terms of orthogonal (Chebyshev) polynomials and nonorthogonal polyn omials is investigated. Finally, a mixed parametric and nonparametric model that exhibits a very satisfactory behavior in the case of import ant hardening and viscous damping is presented.