Keywords: pounding, earthquake, impact model, building.

Very often, especially in densely-resided areas and city centres, neighbouring buildings are constructed very close to each other. Thus, structural pounding may occur, during strong earthquakes, between adjacent buildings due to deformations of their storeys. The consequences of such pounding incidences, ranging from local light damage to severe structural damage or even collapse, have been observed and reported in past strong earthquakes. Pounding may also occur in cases of seismically isolated buildings when the available width of the provided seismic gap around them is limited, while larger than expected horizontal relative displacements occur at the isolation level during very strong seismic excitations.

Several research studies have been conducted in order to investigate, through numerical simulations, the problem of earthquake-induced pounding of neighbouring buildings. A significant part of this numerical problem has to do with the simulation of impacts, the so called "impact modelling". In the case of structural pounding, simple impact models, which estimate the magnitude of the impact forces, are usually used. The most commonly used impact models are based on the "penalty method", in which a small inter-penetration among two colliding bodies is allowed and used in combination with an impact stiffness coefficient to calculate the elastic impact forces that are applied on the colliding bodies.

In this paper, the major "force-based" impact models, which assume either a linear or a non-linear behaviour, are assessed, while two new impact models are presented. The first is a linear viscoelastic impact model, which is actually a minor modification of the widely used Kelvin-Voigt impact model while the second is the non-linear hysteretic impact model, whereas the impact force increases exponentially with the indentation and the kinetic energy is assumed to be dissipated hysteretically during impact.

Moreover, a representative example of a seismically isolated building pounding against the surrounding moat wall during a strong earthquake excitation is considered in order to examine the effect of using different types of impact models on the overall response of the structure during impacts.

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