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High performance base-isolated buildings are designed with a higher level of safety than the conventional fixed-base buildings under the current codes. As a sustainable development, these buildings have considerably lower social and economic impacts in a major event. The main factor limiting the extensive use of such systems is the higher initial construction costs. The cost estimations based on only initial investment may have concluded misleading results as the performance of those systems in earthquakes are different. Therefore, an evaluation considering initial costs and future repair costs due to damages from earthquakes gives a better scope for selection of an optimal design, among different alternatives.
There is an emerging trend in earthquake resistant design of buildings to consider both safety and cost factor using PEER probabilistic approach. This methodology is able to estimate to the probable losses including damages in building components, human injuries and associated costs in a fully probabilistic framework. This study is aimed at performing a cost-benefit comparative study of base-isolated and fixed-base buildings using PEER approach.
Performance of several multi-story concrete moment resisting frames was initially investigated using a cost-based response index or a simplified performance measure. Calculated response indices of base-isolated models were up to 6 times lower than the fixed-base ones for the low-rise 3-story models at the highest hazard level. However, only a slight performance upgrade was achievable for rather high rise isolated building models.
As the main focus of this study, six benchmark office buildings were selected including five fixed-base and one base-isolated model for cost comparison purposes. Different seismic loads are used for the design of fixed-base buildings varying from one to three times the minimum seismic forces according to IBC-2012. The results of Time-Based Assessment shows that the lower long term costs of high performance buildings has the potential to justify their additional initial costs for most of the models. Isolated building performed superior to all fixed-base models in the cost-benefit analysis. Although the initial costs of the isolated model is over 6% higher than the fixed-base basic model, the total net present value of base-isolated building is 4.1% lower at an assumed interest rate of 7%.
Adviser: Terri R. Norton