Earthquake induced pounding in friction varying base isolated buildings.rar

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. c 2007 Elsevier Ltd. All rights reserved. Keywords: Earthquake engineering; Base isolation; Variable friction; Teflon bearings; Building pounding; Impact; Damage 1. Introduction Residential and commercial buildings in metropolitan areas are often built very close to one another, making them at risk of impacting each other when responding to strong ground motion. Further, architectural projections may exacerbate the situation by decreasing the local spacing between the adjacent buildings. It is becoming more common in engineering practice to retrofit mid-rise structures with seismic response modification devices. One approach that has been commercialized over the last decade is the use of base isolators, and in this study the modification of building response behavior with the introduction of variable friction Teflon bearing systems [7] is investigated. Retrofitting or designing new structures using friction bearing units located between the foundation and the superstructure is an effective approach to reduce the force effects of strong ground motions. Friction bearings reduce the  Corresponding author. Tel.: +1 979 862 1463; fax: +1 979 845 8986. E-mail address: j-niedzwecki@tamu.edu (J.M. Niedzwecki). base shear