RESPONSE OF RIGID BLOCK ASSEMBLIES TO EARTHQUAKE EXCITATION

Abstract

The behaviour of free-standing structures modelled by a mechanical system consisting of two rigid blocks put on each other and subjected to forcing at its supports has been studied. In case of the presence of support motion, the blocks may slide and/or rotate (lift up) on each other and/or on the support. The possible types of initial motion and the contact forces for the structure subjected to inertial force caused by support excitation have been calculated by using the basic law of dynamics. As an application example for calculations and the related computer program the analysis of a standard crane of bridge-like structure under earthquake excitation is presented. The risk of overturning of the upper block on the steady lower one is investigated by applying an analytical approach and a formulation of the upper body as inverted pendulum under horizontal base excitation. Furthermore, the lowest natural frequency related to the vertical vibration is calculated for different configurations.