Seismic response and design of base-isolated hillside stilted structures

Established studies and seismic site investigations have revealed that hillside stilted structures suffer more serious damage compared with ordinary structures on flat ground due to their stiffness irregularities. However, studies on mitigating stiffness irregularities and enhancing seismic performance of stilted structures are limited. In this study, isolation bearings are introduced for the first time into the base of stilted columns, forming a base-isolated stilted structure, with the aim of controlling structural seismic response and mitigating stiffness irregularities. A series of shaking table tests were conducted on both a base-isolated stilted frame and a fixed-base stilted frame. Then, the stiffness of a stilted column-bearing tandem system was analyzed to determine the deformation of stilted columns under uniform stiffness distribution conditions. Finally, a direct displacement-based seismic design method for base-isolated stilted frames was proposed, and its validity was verified through time history analysis of 7-storey and 3-storey stilted building design cases. Test results demonstrated that installing seismic isolation bearings at the base of the stilted columns effectively reduced the seismic response of the stilted structure, verifying the effectiveness of the bearing arrangement. The results of the time-history analysis closely match the design values, and the errors in floor shear, displacement, and bearing deformation remain within 10 %, confirming the validity of the design method. Moreover, the difference in shear force among stilted columns of different lengths remains less than 10 %, indicating that using the proposed design method effectively achieves the objective of mitigating stiffness irregularities.