Research On Performance-Based Seismic Design Of Reinforced Concrete Frame Retrofitted With FRP

With the progress of the times, the focus of civil engineering research has gradually shifted from the construction design to retrofit design. Retrofitting the existing buildings is an effective means of reducing the earthquake disaster and the loss of life and property. With the development of fiber composite materials, civil scholars have paid widespread attention to the use of fiber reinforced plastic (fiber-reinforced polymer, FRP) for structural components' seismic retrofit design. However, there are still some drawbacks in the current FRP seismic retrofit design:when using traditional (force-based) seismic reinforced design theory, it can not give targeted FRP retrofit design for different expectations or predict seismic performance (strength, deformation, ductility, energy, etc.) of FRP reinforced concrete structures under different earthquakes; The current FRP seismic retrofit theoretical and experimental researches were restricted to FRP reinforced members, the seismic performance of overall structure was lack of consideration. During the retrofit design with FRP, the designers often overlooked the performance influence of the local component changes to the overall structure, did not grasp the whole building retrofitting and disease treatment from the overall, global perspective. Therefore, the question whether the seismic performance of overall FRP retrofitted structure meets the needs or not is undoubtedly necessary to answer.Performance-based seismic design theory (PBSD) is a new concept of seismic design theory. Based on the importance of the buildings, its core idea is to make the structures have a different future expected seismic capacity and functionality under different earthquakes. In addition, under the expected seismic performance of the structure, the designer can use a variety of new materials, new processes and new construction methods that can as far as possible to satisfy the needs of the community and the users. The design theory can also give full play to the structural designers' initiative and innovation. This article introduces performance-based seismic design theory into the FRP retrofit seismic design theory and carries out related research to the FRP reinforced concrete frame structures. Its main contents and conclusions are the following aspects:(1) The seismic performance of FRP retrofit column and beam were divided in terms of applicability, reparability and security. Using the drift as performance index and introducing significant factors into the quantization of it, the drift limit of PBSD was presented. Under the requirements of the node construction, the performance of FRP retrofit frame was divided into 5 levels:fully operational level, temporarily operational level, repairable level, life safety level and collapse prevention level based on the performance of FRP retrofit column and beam.(2) The plastic hinge model which applies to the FRP retrofit member was presented. The FRP retrofit plastic hinge model is applied to Etabs software feasibility by the numerical example. The numerical example results show that the base shear, deformation capacity which calculates using the proposed model is better than using the default model. The top displacement and the storey drift which using proposed model is smaller than using the default model under the same earthquake.(3) The cross-section stiffness formulas of pre-yield and post-yield were given for reinforced concrete components retrofitted with FRP composites. The formulas' accuracy is confirmed through a series of tests' results. The frame lateral stiffness formula is determined based on the component's cross-section stiffness. Introduce the target lateral stiffness to the performance-based seismic design theory. The target stiffness can be determined according to the target displacement. The amount of FRP reinforcement can be calculated by using the target stiffness and the amount problem of using FRP can be solved apparently.(4) Based on capacity spectrum, a method considering the incremental energy for FRP reinforced concrete frame is proposed. According to the test data, the equivalent damping ratio expression of components retrofitted with FRP composites was fitting out, and can be used to calculate the additional energy dissipation. The whole frame's equivalent damping ratio considering additional energy dissipation is established based on its definition. The seismic retrofit performance of RC frame using FRP composites can be evaluated more accurately by using "fix" frame' equivalent damping ratio.