Abstract: In service period, some structures may exist damages like cracks, and the opening and closing of cracks make the damage display a time-domain nonlinear characteristic. In addition，time-domain model methods mainly provide the characteristic change of degree of freedom of adjacent nodes caused by stiffness damage, but it is difficult to directly show the inter-storey stiffness information. To solve these problems, a damage detection method based on GARCH model and improved penalty index was presented. Firstly, basic theory of GARCH model was described, and the order estimation and the parameter estimation of GARCH model were proposed. Then, the bilinear stiffness characteristic of time-domain nonlinearity was analyzed, and the nonlinear damage identification principle and basic GARCH index of stiffness identification were presented. Finally, an improved GARCH penalty index method was established to enhance the identification reliability for the inter-storey stiffness damage. Simulation and experiment results indicate that the improved GARCH penalty index can well identify the structural nonlinear damage, and the identification effect of the proposed index is obviously better than those of the basic GARCH index and those combined with autoregressive model and the cepstral metric index.

Key words: damage identification; GARCH model; penalty function; nonlinearity; acceleration response