Nonlinear restoring force estimation in civil structures using a high gain observer

Strong ground motions may cause damage to structural elements by cracking or yielding. Hysteresis cycles are a measure of this damage. The present paper uses a class of integral high gain observers to estimate the unknown nonlinear restoring force of a single-degree-of-freedom structure. Simulations are carried out using the Mexico City at SCT (1985) and the El Centro (1940) time history acceleration records as ground motion inputs. Encouraging results are obtained for the state and nonlinear restoring force estimation.