Real‐Time System Identification of Degrading Structures

Abstract

On‐line identification becomes an important issue when structures undergo nonlinear and time‐dependent degrading behavior under large loads. In this paper, a real‐time, time‐domain system‐identification technique is developed to identify time‐varying system parameters for a multidegree‐of‐freedom degrading structure subjected to general dynamic loads, such as earthquakes. A system of second‐order, linear, ordinary differential equations with time‐varying system parameters is solved to generate the system response using the Newmark time‐integration method. Gaussian white noise is added to the response, and the results are used to simulate the measurements. Then, a least‐squares method is employed to estimate the system parameters in real time based on input data and corresponding response measurements with or without noise. Two numerical examples, a single‐degree‐of‐freedom and a three‐degree‐of‐freedom structure subjected to a simulated El Centro earthquake, are considered. The changes in structural stiffnesses for the example problems are identified. Encouraging results are obtained for both cases.