Response Reduction of Secondary Piping Systems in Base-isolated Buildings

The seismic response reduction of a multi-supported secondary system (SS) attached to a base-isolated six-storied building is evaluated for different types of earthquakes. For this purpose, two 3D models of a six-storied building are taken for the analysis; one is fixed base and the other is base isolated. Lead rubber isolator is used for the isolation. Both buildings support a secondary system (SS), which is a fluid pipe running along with the height on one side of the building (PS). Both buildings are analysed under the bi-directional earthquake ground motions with different ratios of ground acceleration in two directions. Considering the full interaction between the PS and SS, the nonlinear time history analysis is carried out in SAP 2000 to obtain different response quantities of interest at different levels of the PGA. The efficiency of the base isolation in reducing the responses of the SS is investigated by comparing the responses between the SS mounted base-isolated and fixed-base buildings. The responses include the maximum absolute acceleration, maximum relative displacement, maximum stresses developed at the critical sections of the pipe and maximum storey drift. In addition, the difference between the floor response spectra of the two primary systems is investigated. Results of the numerical study indicate that the use of base isolation system in the PS provides considerable protection to the SS. It reduces the peak stresses of the SS at critical sections by about 60-70%.