Conventional concentrically braced frame (CBF) systems designed following current practice can achieve life safety performance but have limited drift capacity prior to structural damage in case of an earthquake event. This structural damage (that is permitted in current design practice under the design-basis earthquake) will not lead to direct collapse of the structure, but often results in residual drift and non-structural damage, causing high post-earthquake direct and indirect costs. This proposal plans to pursue research in demonstration of benefit of self-centering concentrically braced frame (SC-CBF) system rather than a CBF for earthquake-resistant structures. The demonstration of benefit will be judged through performance-based earthquake engineering (PBEE) and through life cycle cost analysis of the system. The project will consider parameters of probabilistic ground motions, various configurations of SC-CBF, and considerations of uncertainties including structural properties, statistical processes, and capacity/demand models. A key element of this project is to assess life-cycle cost benefit of SC-CBF against CBF. The life cycle cost will include direct cost of damage as well as indirect economic losses in case of an earthquake event. The interdisciplinary research team includes structural and geotechnical expertise as well as economics/accounting expertise. The graduate and undergraduate students working on the project will benefit from the interdisciplinary efforts.
The proposed work will evaluate the effectiveness of SC-CBF systems in terms of seismic performance and financial benefits. The proposed research includes several tasks: 1. Selecting suites of probabilistic ground motions for a site that capture the uncertainties relating to magnitude, distance, soil type, and local effects, to incorporate the stochastic nature of the seismic loading. 2. Consideration of a full range of parameters in the development of SC-CBF designs and the associated nonlinear finite element models. 3. Development of unbiased probabilistic capacity and demand models for SC-CBF systems that properly account for prevailing uncertainties in structural property as well as in statistical procedures, in randomness of the ground motions, and in errors in the capacity and demand models. 4. Conducting damage and loss analyses based on the seismic fragility assessed using the proposed capacity and demand models. 5. Comparison of the life cycle cost of several SC-CBF systems with conventional CBF systems through a case study. Uncertainty in all assessment stages will be examined simultaneously, thereby integrating the entire framework into a single interdisciplinary probabilistic model. This integration combines economic considerations in earthquake engineering with the geotechnical and structural engineering principles. The validation of the SC-CBF system based on life cycle costs will have impact on its use by the industry.
