Gradient algorithm for structural parameter estimation and nonlinear restoring forces

Civil structures undergo hysteresis cycles due to cracking or yielding when subjected to severe strong motions. Seismic instrumentation, structural monitoring and system identification techniques have been used in the past years to assess damage. The present research proposes a gradient algorithm to simultaneously identify the combined driving and nonlinear restoring forces, and structural parameters, such as damping and stiffness in a single-degree-of-freedom structure. Simulations are carried out using the EJ Centro (1940) and the Mexico City (1985) seismic records. Encouraging results are obtained for the identification of the parameters and the estimation of the driving and restoring forces.