USING RIGID BLOCK MODEL WITH MASS ECCENTRICITY IN DYNAMIC ANALYSIS OF HOSPITALS - EQUIPMENT UNDER SIMULTANEOUS EFFECT OF HORIZONTAL AND VERTICAL GROUND EXCITATIONS

Abstract eng:
Appropriate performance of hospitals is of crucial importance in the aftermath of earthquakes. On the other hand, proper performance of a hospital is quite dependent on the operation of its nonstructural equipment and components. Therefore, in the studies of seismic performance of hospitals, either for design of future hospital or for evaluation of the existing ones, consideration of seismic performance of equipment is a must. Many of hospitals’ equipment have a rigid block configuration. In this study the ‘rigid block model’ is used for molding some special equipment of hospitals, which have non-uniform distribution of mass or ‘mass eccentricity’. Medicine cupboard and ventilator in surgical operating room are samples of this type of equipment. Studying the seismic behavior of this kind of rigid block is quite complicated due to geometrical nonlinearity. In the previous studies, the seismic behavior of this type of rigid blocks has been investigated by using only a single horizontal component of the earthquake excitations and the effect of vertical component has been neglected. This is while in the case of near-source earthquakes usually the vertical component of ground motion can be very strong. In this study the complex behavior of rigid blocks with non-uniform distribution of mass is studied subjected to simultaneous horizontal and vertical components of ground motion, and the results are compared with those of the case of using only one horizontal component. At first the governing equation of motion have been derived, and then by using some selected earthquake records, the seismic response of the rigid block has been obtained employing fourth order Runge-Kutta-Nistrom technique. Numerical results show that the response of the rigid block is very sensitive to the amount of mass eccentricity on the one hand and the specifications of the ground excitations on the other. Results also show that in many cases the effect of vertical ground motion can lead to toppling of the block, while the horizontal component alone cannot overturn the block.

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