Reliability

Fiber-reinforced polymer composites can be externally bonded to reinforced concrete members which provide an effective seismic retrofit strategy for reinforced concrete structures. For seismic retrofit of a complex building structure, due to the large number of structural members, an optimum design which ensures the use of the minimum amount of fiber-reinforced polymer to achieve a given level of seismic performance is highly desirable for economic reasons. In addition, such an optimum design approach is best built on a probabilistic basis so that various sources of uncertainties in the design process can be appropriately accounted for. This work therefore studies an efficient reliability-based optimization approach for the seismic retrofit design of reinforced concrete structures using fiber-reinforced polymer composites. The structural performance is assessed at the system level using nonlinear pushover analyses. In the proposed approach, the inelastic interstory drift ratios are modeled as indeterministic variables to consider the uncertainties of earthquake loading. By contrast, the thickness of the fiber-reinforced polymer jacket is considered as a deterministic design variable. The reliability-based design approach is formulated by minimizing fiber-reinforced polymer cost subject to prescribed structural reliability constraints. Using the results of nonlinear static pushover analyses and reliability analyses, the reliability index constraints are explicitly formulated with respect to the deterministic design variables based on the virtual work principle as well as Taylor series expansion. A numerical optimality criteria method is derived and programmed to solve this reliability-based nonlinear retrofit design optimization problem. A design example is included to illustrate the application of the new optimization approach