This article investigates the influences of the effective ground motion duration (GMD) on damping reduction factor. The GMD are associated with 25 Chi-chi earthquake ground motion records and harmonic sine wave. The study shows that damping reduction factor decreases with the increasing of the damping ratio, and decreases with the increasing of the effective duration of the ground motion and the number of cycles of harmonic excitation. A nonlinear multiple regression analysis based on the statistical mean values of the present study is employed, and a modified damping reduction factor considering the effects of GMD is suggested.

Due to the serious impact of metro vibration on people’s lives, it is important to design vibration isolators. In this study, the dynamic characteristics of a thick-walled ring spring are studied first. Through theoretical derivation, a new formula suitable for thick-walled ring springs is proposed. Finite element numerical analysis was performed to study the load–displacement curve and stress of the ring spring and verified the correctness of the formula. According to the studied mechanic characteristics, a novel ring spring isolator is proposed for vibration isolation of the metro superstructure. With the help of a ring spring, the proposed isolator has good energy absorption and self-reset function. The dynamic simulations were conducted in a multi-story building with the ring spring isolator as the isolator to study the vibration performance. It is common knowledge that the vertical natural frequency of the superstructure that is isolated by compression springs is given by the mass of the superstructure and the spring stiffness. In order to obtain vibration attenuation and control the vertical deformation, the spring stiffness needs to be 500–1000 kN/mm. Hence, it is clear that the vibration isolator does reduce the vertical eigenfrequency. By comparing the isolated structure with the non-isolated structure, it is proved that the new isolator can effectively improve a building’s serviceability.

This paper reports on investigations into seismic ductility reduction factors for MDOF systems. Ductility reduction factors for MDOF systems are obtained by modifying ductility reduction factors of SDOF systems through a modification factor. Based on China's seismic code, MDOF lumped-mass shear-type models are introduced and employed to study the modification factors that can be used to calculate the lateral strength demand of MDOF systems. The four main parameters of site characteristics, number of storeys, displacement ductility ratio and fundamental period of the system, have been investigated to gain insight into the modification factors. It is demonstrated that ductility reduction factors for MDOF systems are clearly smaller than those for SDOF systems. The modification factor is mainly affected by the number of storeys, and the fundamental period. The ductility ratio also has an important influence on the modification factor and can't be neglected. Analysis results also indicate that the coefficient of variation for the modification factor increases with increasing number of storeys, fundamental period and ductility ratio. Finally, based on the results of a comprehensive statistical study on modification factors a simplified expression is suggested, which can conservatively estimate the modification factor required.

This paper reports on investigations into seismic ductility reduction factors for vertically irregular multi-degree-of-freedom (MDOF) systems subjected to pulse-like ground motions. Ductility reduction factors of irregular MDOF systems are obtained by modifying those of reference regular MDOF systems through a modification factor. Specifically, the structural vertical irregularities are introduced by changing the combined-strength-and-stiffness at the first storey of a reference regular system. The five main parameters of irregularity ratio, ductility ratio, fundamental period, storey number and velocity pulse of ground motions, have been investigated to gain insight into the modification factors. It is demonstrated that ductility reduction factors for irregular MDOF systems are clearly smaller than those for regular MDOF systems. The modification factor is mainly affected by irregularity ratio, and ductility ratio, decreasing with decreasing irregularity ratio and increasing ductility ratio. However, the storey number and fundamental period are observed to have little influence on this modification. Finally, based on the statistical results of pulse-like and non-pulse-like cases, reference values of the modification factors are suggested, which can somehow accounts for the effects of vertical irregularity and velocity pulse on ductility reduction factor in engineering application.

This article investigates the ductility reduction factors for RC eccentric frame structures subjected to pulse-like ground motions. The structural models are with the strength eccentricities which are much disadvantageous than the stiffness eccentricities during the inelastic response range. A method to determine the ductility reduction factors of the strength eccentric structures is suggested by modifying those of reference symmetric structures through an eccentricity modification factor. The four factors of strength eccentricity ratio, ductility ratio, story number and velocity pulse of ground motions, are investigated to gain insight into this modification factor. It shows that the ductility reduction factors of the eccentric structures are clearly smaller than those of the symmetric structures. The eccentricity modification factor is mainly affected by the strength eccentricity and the ductility ratio, decreasing with the increment of the eccentricity or the decrement of the ductility ratio in a medium eccentricity range. The earthquake pulse-like effect and the eccentricity have coupling influence on the modification factor, while the effect of story number is not apparent. Based on the results of a comprehensive statistical study a simplified expression is suggested, which can estimate the eccentricity modification factors for both pulse-like and nonpulse-like ground motion cases.