Parametric identification of asymmetric buildings from earthquake response records

This paper aims to evaluate the modal frequencies, damping ratios and mode shapes of an asymmetric building, modeled as general torsionally coupled buildings using a modified random decrement method together with the Ibrahim time domain technique based only on few floor acceleration response records from earthquakes. It is not necessary to measure earthquake excitation input. The general relationship between the reduced random decrement signature and the true free vibration response is derived analytically. Because only partial floor response measurements are used, a mode shape interpolation technique is developed to estimate the mode shape values for the locations without measurement, such that all floor responses can be obtained. The results were obtained from simulation data from a five-story building under the 1940 El Centro earthquake and actual records from a seven-story RC school building in north-eastern Taiwan, due to an earthquake near the building site. The results show that the proposed system identification technique is capable of identifying structural dominant modal parameters and responses accurately even with highly coupled modes and high levels of noise contamination.