Experimental and analytical studies of structures seismically isolated with an uplift-restraint isolation system

Notwithstanding its pervasive influence on seismic-resistant engineering, the efficacy of seismic isolation in structures subjected to strong ground excitation, including near-fault effects, is potentially compromised by excessive overturning moments capable of inducing undesirable uplift or tension in isolation bearings. This dissertation aims at extending the scope of seismic isolation by studying a novel sliding isolation bearing, denoted as XY-FP, capable of sustaining tensile forces, thereby preventing uplift. To demonstrate the validity of the concept and provide evidence for the effectiveness of the XY-FP isolator in uplift restraint, an extensive testing program on the earthquake simulator at the University at Buffalo was conducted on a slender quarter-scale five-story base-isolated model structure. The range of tests conducted represents the only available experimental data on XY-FP isolators and form the basis for comparison with and validation of analytical predictions. A comprehensive mathematical model capable of accommodating the mechanical behavior of the XY-FP isolator was developed and implemented in program 3D-BASIS-ME. The validity of the analytical model with reference to the newly introduced element representing the XY-FP isolator was investigated by comparison of analytical predictions with experimental results. The good agreement attests to the accuracy of the analytical model, evident even under extreme dynamic conditions entailing tension in the isolators. This demonstrates that the behavior of the XY-FP isolator is sufficiently well understood to allow for accurate prediction of the response of isolated structures incorporating the new isolation devices. Finally, a case study involving nonlinear response-history analysis of a seismically isolated structure subjected to bi-directional horizontal seismic excitation is presented to assess the impact of XY-FP isolators on the response of a real structure.