A Study of the Intensity Index of the Strong Ground Motions that Property Evaluates the Seismic Damage of Structures

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The seismic damage of structures depends on the characteristics of seismic motions, such as intensity and spectrum, and structural qualities, such as the natural period and the damping ratio. There was no effective intensity measure of the strong ground motions that adequately evaluates seismic damage of structures in the wide range of the natural periods.We propose the modified maximum impulse defined as the minimum value of the maximum impulse in strong ground motion and the product of the peak ground acceleration and quarter of the natural period of a structure. The relationship between several measures and the damage of single story, three stories, five stories and seven stories structures which story restoring characteristics are bilinear model is analyzed by the time history analysis using seventy three strong ground motions that are recorded in Japan, United States and Taiwan which peak ground accelerations are almost greater than 3 m/s/s. The damage measure of a structure is used the yield shear force in the first story that related to the maximum ductility factor in the all stories.The modified maximum impulse is the most effective measure that evaluates the damage of structures than other measures, such as the peak ground acceleration, the peak ground velocity, the velocity spectrum and the spectral intensity in the first natural period from 0.1 second to 1.0 second. The correlation coefficients between the modified maximum impulse and the yield shear force that is related to the ductility factor of 2.0 or 5.0 is greater than 0.8. This result shows that the modified maximum impulse is the most effective measure for the selection of intensity level of the strong motion in the time history analysis.