PERFORMANCE BASED DESIGN OF BASE ISOLATED HOSPITAL BUILDINGS

Abstract

Hospital buildings are of great importance after any natural calamity. The structural and non structural components should remain operational and safe. Performance Based Design (PBD) has evolved over past few years which ensure a specific Performance Level. This is a development over the Force Based Design and implies that deformation is a more realistic indicator of the damage in the building. In PBD, the performance of structural components is controlled by limiting the inelastic deformations, while that of non-structural components is controlled by limiting the inter-storey drift and floor acceleration. The present study has been concentrated on PBD of hospital buildings, which require stringent design performance levels. The structural components have to satisfy Immediate Occupancy level while the non structural components have to be ensured Operational performance level. For Operational performance of nonstructural components, the drift limit for hospital buildings should be within 1%. A four storey and an eight storey building, with identical plans, have been considered for the study. An iterative procedure has been developed for the PBD of fixed base buildings to achieve the desired performance levels. The performances have been evaluated using Non-Linear Static and Dynamic analyses. The Performance Point evaluated using Push-Over Analysis has ensured the hinges to be below IO level and the inter storey drift has also been limited.to 1%.This has been verified using the Time History Analysis. It has been shown that in case of fixed base building, it is possible to control the member plastic deformations and inter-storey drifts within the desired limits, but the floor accelerations get amplified and it is not possible to control all the three parameters simultaneously. This can be achieved only through Base Isolation. However, there are a number of parameters including the proportioning of superstructure and design of the base isolation system, which are to be controlled in design. This is iterative procedure which requires a large number of iterations. In the present study, a design method, based on the Displacement Based Design method proposed by Priestley, has been evolved, which can lead to the structural configuration with desired performance in a few 111 iterations. The super-structure has been designed in such a way that it satisfies 10 level and the drift limit. At the same time, the base isolation has been designed to limit the Peak Floor Acceleration. The method has been applied to the two buildings with 4 and 8 storeys.