Earthquake induced pounding in friction varying base isolated buildings

The earthquake induced upper story pounding response of two buildings in close proximity is investigated. The formulation models each building as two degree of freedom oscillators and allows for impact at mid-level and top-level elevations. Variable friction base isolation modeling Teflon bearings are introduced into the formulation and it is assumed that the earthquake induced motion is one dimensional in that it excites each building from the same direction for each building. Three illustrative examples are presented that provide a basis for comparison of fixed base and base isolated buildings models. In the numerical simulations, four earthquake records from different sites were used to excite the buildings and were scaled to the same spectral acceleration at the period of the fixed-base building natural period in order to provide a common seismic hazard level. The number of upper story building collisions is presented as a function of the gap spacing between the buildings, and results illustrate the effect of altered structural kinematics due to impact. The number of upper story impacts for the fixed base and the base isolated structure configurations and the effect of friction varying base isolation on the number of building impacts is shown through example to be a function of earthquake ground motion specifics.