SEISMIC BEHAVIOUR OF BUILDINGS ON HILL SLOPES

Abstract

Due to scarcity of flat land in hilly areas, majority of the buildings is constructed on the hill slopes. Such buildings pose special structural and constructional problems. Dynamic characteristics of hill buildings are different from the buildings resting on flat topography, as these are irregular and unsymmetrical in both horizontal and vertical directions. The irregularvariation of stiffness and mass m vertical as weir as norizoniai directions, esult ~iin centre of mass and centre of rigidity of a storey not coinciding and not being on a vertical line for different floors. When subjected to lateral loads, these, buildings result in significant torsional response. This work is an attempt to understand the behavior of hill buildings using analytical investigation. A brief review of the literature available on geometrical configuration of buildings resting on sloping ground, setback and step-back buildings, and torsional coupling of asymmetric buildings is also presented. A 9 storey RC frame building with two different hill configurations, and two regular buildings resting on flat ground with 3 and 9 storeys having same plan as the hill buildings, are considered for analytical investigation. Dynamic response of hill buildings is compared with that of regular buildings on flat ground, in terms fundamental period of vibration, pattern of inter-storey drift, column shear, and hinge formation pattern by subjecting them to a set of five earthquake time histories. In order to study of seismic performance of hill buildings, incremental nonlinear dynamic analysis is performed for a suite of twenty bi-directional scaled ground motion records. Selection and scaling of ground motion records and step by step procedure to perform the incremental dynamic analysis is also discussed. The dynamic pushover curves between spectral acceleration and spectral displacement are plotted to understand the complete range of behavior of buildings in elastic as well as in=elastic range. Different configurational modifications to avoid torsional and stiffness irregularities in hill buildings, are also studied using a parametric study by placing shear walls at different locations and varying the height of ground supported columns. The behavior is studied in terms of Amax/Davg ratio and distribution of column shears. Application of iii bracings to avoid irregularities in hill building configuration is also explored. It is observed that shear walls on uphill side are more effective in reducing shear force in ground supported column in hill building, as compared to the shear wall placed on down-hill side along the slope direction. Increasing the height of ground supported columns and placing the shear wall on the down-hill side of hill building resulted in torsinally balanced configuration and shear force in ground supported columns also reduced to reasonable level.