Earthquake-resilient design of base isolated buildings with TMD at basement: Application to a case study

The earthquake-resilient design of a reinforced concrete framed building is presented in this paper as a case study. A non-conventional application of the base isolation in conjunction with a tuned-mass-damper (TMD) located at basement, below the isolation floor, is studied for improving the seismic performance of the building. The seismic base isolation is implemented below the first story, with low-damping rubber isolators mainly placed throughout the perimeter of the building. At the center of the building a large-mass TMD is inserted, which consists of a box filled with large aggregate concrete. The box is located at basement and is connected to the base isolation system via an auxiliary set of lead-core rubber isolators, the latter playing the role of damper and spring elements of the TMD. The TMD box is disconnected from the ground via low-friction flat sliding devices. Optimal design parameters of the auxiliary TMD isolators are detected by minimizing an objective function that is based on the stochastic dynamic analysis of a simplified three-degree-of-freedom system comprising the main structure, the base isolation and the TMD. Four different objective functions are investigated, including the main structure displacement relative to the ground, the interstory displacements, the total acceleration and an energy-based indicator. The effectiveness of this design philosophy and of the related optimization procedure, first time applied to a real case, is demonstrated via nonlinear time-history analyses with simulated accelerograms being consistent with the response spectrum of the installation site. Advantages of this structural system over both the fixed-base building and the conventional application of the base isolation are shown in terms of a variety of response indicators summarizing the seismic performance of the building, including the deformation of the isolators, the displacement demand of the structure, the base shear, the interstory drifts, and the shear forces and bending moments on the beam-column members.