Effect of Foundation Fixity on Buildings on Hill Slopes Under Earthquake Shaking

Abstract: Buildings located on hill slopes often encountered huge damages from past earthquakes due to their irregularity in elevation and plan. Building code provisions do not specify any separate design guidelines for these buildings except by limiting the height for estimating natural periods; this ensures stiffer and stronger buildings. Sometimes, landslides are accompanied by earthquake effects or due to heavy rains. The boundary conditions of these building changes suddenly (e.g., fixed to roller) leading to catastrophic damage. Therefore, this study aims to identify the behaviour of buildings on hill slopes designed based on existing code provisions with fixed boundary conditions and asses its performance by suddenly varying the boundary conditions (e.g., pinned or roller). Four different type of building configurations studied includes (a) building on plain ground, (b) step-back building, (c) step-back setback building and (d) step-back building on steep slope. The masonry walls are modelled as an equivalent strut. Elastic and inelastic behaviour of these buildings are obtained using Equivalent Static (ES), Response Spectrum (RS), Nonlinear Static (NLPoA) and Nonlinear Time History (NLTHA) Analyses. Based on the stress resultants, elastic and inelastic storey drifts, and level of damages in structural elements, the change in boundary conditions of buildings causes unusual behaviour or sometimes collapse without any warning. Also, change in fixity causes poor energy dissipation in stepback building, and with acceptable level of damages in other buildings on slopes. Step-back setback building performed better than other configurations. Therefore, code provisions must consider placing an additional provision including the effect of foundation fixity for buildings on hill slopes. It may be validated through building models considering soilstructure interactions.