Optimal performance-based design of FRP jackets for seismic retrofit of reinforced concrete frames

Abstract

External bonding of fiber-reinforced polymer (FRP) composites is now a well-established technique for the strengthening/retrofit of reinforced concrete (RC) structures. In particular, confinement of RC columns with FRP jackets has proven to be very effective in enhancing the strength and ductility of columns, and has become a key technique for the seismic retrofit of RC structures. Despite the large amount of research on the behavior of RC columns confined with FRP, little research has been conducted on the behavior of RC frames with FRP-confined columns. For the seismic retrofit of RC frames with FRP, apart from the structural response of a retrofitted frame, an important issue is how to deploy the least amount of the FRP material to achieve the required upgrade in seismic performance. With these two issues in mind, this paper presents an optimization technique for the performance-based seismic FRP retrofit design of RC building frames. The thicknesses of FRP jackets used for the confinement of columns are taken as the design variables, and minimizing the volume and hence the material cost of the FRP jackets is the design objective in the optimization procedure. The pushover drift is expressed explicitly in terms of the FRP sizing variables using the principle of virtual work and the Taylor series approximation. The optimality criteria (OC) approach is employed for finding the solution of the nonlinear seismic drift design problem. A numerical example is presented and discussed to demonstrate the effectiveness of the proposed procedure.