A modified Kelvin impact model for pounding simulation of base-isolated building with adjacent structures

Base isolation can effectively reduce the seismic forces on a superstructure, particularly in lowto medium-rise buildings. However, under strong near-fault ground motions, pounding may occur at the isolation level between the baseisolated building （BIB） and its surrounding retaining walls. To effectively investigate the behavior of the BIB pounding with adjacent structures, after assessing some commonly used impact models, a modified Kelvin impact model is proposed in this paper. Relevant parameters in the modified Kelvin model are theoretically derived and numerically verified through a simple pounding case. At the same time, inelasticity of the isolated superstructure is introduced in order to accurately evaluate the potential damage to the superstructure caused by the pounding of the BIB with adjacent structures. The reliability of the modified Kelvin impact model is validated through numerical comparisons with other impact models. However, the difference between the numerical results from the various impact analytical models is not significant. Many numerical simulations of BIBs are conducted to investigate the influence of various design parameters and conditions on the peak inter-story drifts and floor accelerations during pounding. It is shown that pounding can substantially increase floor accelerations, especially at the ground floor where impacts occur. Higher modes of vibration are excited during poundings, increasing the inter-story drifts instead of keeping a nearly rigid-body motion of the superstructure. Furthermore, higher ductility demands can be imposed on lower floors of the superstructure. Moreover, impact stiffness seems to play a significant role in the acceleration response at the isolation level and the inter-story drifts of lower floors of the superstructure. Finally, the numerical results show that excessive flexibility of the isolation system used to minimize the floor accelerations may cause the BIB to be more susceptible to pounding under a limited seismic gap.

Underground blast effects on structural pounding

In the present study,actual three-dimensional structures are converted into a stick model of multi degree of-freedom(MDOF)systems for understanding the macro-behavior of structures.The study investigates the performance of three closely spaced,adjacent G+10,fixed-base MDOF systems with the mass aligned at the same levels and subjected to accidental underground blast loading.The acceleration time history of underground blast loading is generated based on past empirical relationships.The blast charge weight varies from 10 to 75 t while keeping the charge distance constant(R=100 m).The entire formulation is solved with the MATLAB solver,using the state space form solution.Three cases are considered,based on changing the position of the three stick systems.The first case considered left building rigid,middle building moderate rigid,and right building flexible.The second assumed left building flexible,middle building rigid,and right building moderate rigid.The third examined the left building as moderate rigid,the middle building as flexible,and the right building rigid.An analysis of the results shows that the arrangement with low stiffness,high stiffness,and moderately stiff buildings placed to the left,middle,and right side,respectively,yields minimum structural response when compared to the other two combinations.

Impact analytical models for earthquake-induced pounding simulation

Structural pounding under earthquake has been recently extensively investigated using various impact analytical models.In this paper,a brief review on the commonly used impact analytical models is conducted.Based on this review,the formula used to determine the damping constant related to the impact spring stiffness,coefficient of restitution,and relative approaching velocity in the Hertz model with nonlinear damping is found to be incorrect.To correct this error,a more accurate approximating formula for the damping constant is theoretically derived 5~nd numerically verified.At the same time,a modified Kelvin impact model,which can reasonably account for the physical nature of pounding and conveniently implemented in the earthquake-induced pounding simulation of structural engineering is proposed.