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Word Count: 333
Nonlinear dynamic response of base-isolated rigid blocks underhorizontal motions is presented in this paper The structural model iscomposed of a rigid block supported by a rigid base and an isolationsystem which decouple the rigid base from the ground The dynamicresponse of the system causes through two distinct oscillation patternspure translation the base-block system is translated as a whole androcking the block pivots on its edges with respect to thehorizontally-moving base The equations of motion for each oscillationpattern are formulated by using the Lagrange method Sliding of theblock relative to the supporting base is neglected The dynamic responseof the system is strongly affected by the occurrence of impact betweenthe block and the horizontally-moving base Impact renders the problemhighly nonlinear as it causes the system to switch from one oscillationpattern to another modifying the degrees of freedom and the systemsvelocity regime In addition impact acts as an energy dissipationmechanism for the system through the reduction of post-impactvelocities Hence a meticulous formulation of the impact problem isrequired which is derived from the first principles using classicalimpact theory Two equivalent models of seismic isolation are utilizedin the analysis of the system namely a linear model with viscoelasticbehavior and a nonlinear model with hysteretic behavior FrictionPendulum System FPS is preferred for the simulation of the nonlinearisolation system The hysteretic behavior of the FPS is described byBouc-Wen model The two isolation systems are comparable as theeffective stiffness and the equivalent damping factor of the FPS is thesame with the stiffness and the damping factor of the linear isolationsystem respectively The numerical integration of the governingequations of motion is accomplished using Matlabs ordinary differentialequation solver ODE45 which is an implementation of fourthfifth-orderRunge-Kutta method A comparison based on the response of the systembetween the two equivalent models is achieved using diverse seismicexcitations and physically realizable pulse-type motions
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