A direct displacement-based design procedure for base-isolated building structures with lead rubber bearings (LRBs)

This paper proposes a direct-displacement based design (DDBD) procedure, to make base-isolated building structure with lead-rubber bearing (LRBs) satisfy the performance objectives prescribed by displacement thresholds. To this end, the DDBD for regular building structures is incorporated with the two-degree-of-freedom (2DOF) model of base-isolated building structures. Fundamentals of the standard DDBD procedure is briefed at first. The equivalent linearized 2DOF model of a base-isolated building structure is then detailed. Modal analysis and response spectrum analysis of this 2DOF model has been carried out, which suggests a simplistic and readily-invertible closed-form relationship from structural characteristics to seismic displacements. Given the displacement requirements, the relationship facilitates the solution of the structural parameters of the base-isolated building structure. Following the basic steps of DDBD but utilizing this 2DOF model as the substitute for the original nonlinear structural model, an alternative DDBD procedure is then developed and detailed. This DDBD procedure is verified by numerical examples, in which the nonlinear time-history analysis of the designed structures yields seismic displacement results matching the preset target thresholds well. The design solutions of the proposed procedure are also compared with those given by an existing one. Numerical results indicate that the proposed DDBD procedure is reliable, straightforward, and convenient for the seismic design of base-isolated building structures with LRBs.