Maximum drift estimation based on only one accelerometer for damaged shear structures with unknown parameters

This paper presents a method to estimate the maximum inter-story drift and relative displacement time history of multi-degree-of-freedom (MDOF) shear structures underground-motion excitation by using only one accelerometer installed on a floor when the structures are damaged during the event and hence modal parameters change and become unavailable. First, the absolute acceleration and relative displacement are formulated in modal coordinates and a state-space expression is derived. Then, a scheme to determine the unknown natural frequencies of the damaged structure is devised with the help of the genetic algorithm (GA) and a reasonably chosen fitness function, and the mode shapes are updated by solving a set of nonlinear equations with respect to each group of frequency variables in the GA. The applicability of this method was studied in numerical simulations that examined the effect of the extent of damage to the structure and the selection of the lower bound of the GA variables. Further simulations were conducted to investigate the modal truncation error and robustness against measurement noise of the proposed approach. Finally, the method was validated in a shake table experiment. The results indicate that the time history of the relative displacement and maximum inter-story drift can be accurately estimated in the case of a significant reduction in structural stiffness and a large search range of GA variables. The results also show the method is robust against noise and performs well even when only the lower modes are included in the model.