Study On Intensity Measures For Velocity Pulse-like Earthquake Ground Motions

The research on intensity measures (IM) has developed from single scalar and ordinary earthquake ground motions to vector and velocity pulse-like earthquake ground motions, with its analysis object evolving from single-degree-freedom (SDOF) systems to multi-degree-freedom (MDOF) systems. Since there are not many foreign and domestic researches on intensity measures (IM) for velocity pulse-like earthquake ground. Based on dynamic time analysis of SDOF systems and shear type MDOF systems subject to velocity pulse-like earthquake ground motions, this paper researched velocity pulse-like earthquake IM by using probability statistical analysis. The main research contents and conclusions are as following:1. The correlation between intensity measures (IM) for velocity pulse-like earthquake ground motions and nonlinear deformation demand of SDOF systems is researched, and the efficiency of IM is described. Based on dynamic time analysis of SDOF systems subjected to 72 velocity pulse-like ground motions, this work investigates the variation trend of the correlation coefficient between IM for velocity pulse-like ground motions and maximum nonlinear deformation demand of SDOF with the constant-ductility or constant-strength system setting. Linear regression analyses are performed on these results to identify the efficiency of peak ground velocity (PGV) and spectral acceleration (Sa(T1)), which is used as IM for pulse-like ground motion. The study shows that IM of velocity pulse-like ground motions depend distinctly on the system period, ductility levels and strength reduction factors have important influence on the correlation and dispersion, and Sa(T1) and PGV are relatively the good IM for velocity pulse-like ground motion.2. The correlation between intensity measures (IM) for velocity pulse-like earthquake ground motions and nonlinear deformation demand of shear type MDOF systems is researched, and the efficiency of IM is described. Based on the nonlinear dynamic time analysis of MDOF systems subjected to 20 large velocity pulse-like ground motions, this work investigates the variation trend of the correlation coefficient between IM for velocity pulse-like ground motions and maximum nonlinear roof drift demand of MDOF systems with the constant-ductility system setting. Linear regression and dispersion analyses are performed on these results to identify the efficiency of IM for pulse-like ground motions. The study shows that the fundamental period and ductility level of structure have important influence on the correlation and dispersion. When PGV is used as IM for pulse-like ground motions, the correlation and dispersion is relatively stable with the large relative coefficient and the small dispersion.3. Nonlinear displacement biases in response of SDOF systems are studied, which are resulted from scaling the velocity pulse-like ground motion records. Based on dynamic time analysis of SDOF systems subjected to 30 velocity pulse-like ground motions, this work investigates the variation rules of the nonlinear displacement biases versus structural vibration period (T) and strength reduction factor (R) after scaling the earthquake records to the levels of target spectral acceleration (Sa), peak ground acceleration (PGA), peak ground velocity (PGV), and peak ground displacement (PGD). The variation trends of displacement biases are determined by log-linear regression of scattered points, and the stability of the biases under the condition of scaling different ground motion intensity measures are comparatively analyzed. The results demonstrate that the amount of displacement biases greatly depend on the scaling factor, the first-mode period of vibration, and overall strength of the structure. Reasonable scaling factor and reasonable ground motions intensity measuring parameter of the velocity pulse-like ground motion records can effectively reduce the calculated displacement bias in structural earthquake responses.