Identification of seismic damage to structural buildings using quasi-Newton method

摘要

In order to restore damaged buildings affected by earthquake excitations, it is important to identify damaged elements in terms of their dynamic properties; stiffness, mass and damping coefficients. In this paper, a simple method is proposed for identification of the damaged parts. By considering all unknown dynamic properties of structure as variables {X} of a target function f in nonlinear programming problem, the damage identification problem can be replaced by a typical unconstrained minimization problem. The target function is defined as f= Σ ({y_(n,i)} -{y_n~*})~2, where {y_(n,i)} is structural response at the time of t=Δ x n derived from i-th trial variable {X_i}, and {y_n~*} means observed (or exact) response, respectively. In order to achieve quick convergence, quasi-Newton method and BFGS formulae are adopted for minimizing the target function. Two decision problems are discussed. One is the choice of structural response; displacement, velocity or acceleration. The second is the kind of external excitations that should be adopted. By observing three dimensional graphics. It appeared that good convergence can be achieved by adopting displacement response and sinusoidal excitation. Furthermore, it appeared that we should not evaluate the identified properties only from the response diagrams