Simulation of structural pounding with the sears impact model

Abstract

Seismic pounding affects some buildings and bridge spans with insufficient expansion joints. During pounding, structures exert repeated hammer-like blows on adjacent structures or structural elements which causes a range of effects from minor cosmetic spalling to major structural damage in buildings while bridge spans may be unseated. Several methods have been proposed for numerical simulations of pounding. The most common method is the contact element model, where a link is introduced between the pounding masses to allow simulation of the contact force. Unfortunately, most of these models have been developed based on the collision of spheres, idealized as concentrated masses, while the pounding structures have distributed masses. These models also suffer from uncertainties regarding the stiffness of the links and the duration of contact as well as the amount of energy lost during contact. Some studies have also proposed a pounding model as an impact between two bars whose response is governed by stress wave propagation. These models can predict the energy loss during impact and the duration of impact but have a major drawback that the strain in the bars rises instantaneously to a finite value, which results in an infinite acceleration. Similarly, they can predict a negative value of the coefficient of restitution which makes no sense from a physical stand-point. This paper proposes a quasi-empirical impact mechanism for simulation of structural pounding. The model includes the effects of both the contact surface properties and the crosssectional properties of the bars. The pounding force is calculated from the deformation and stiffness at the contact location, but the duration of contact and the development of the local deformation is a function many factors for which a parametric analysis is presented. Finally, an example of a building pounding analysis with the proposed model is provided.