Reinforced concrete frame connections rehabilitated by jacketing

Recent earthquakes in many parts of the world have demonstrated the vulnerability of existing structures to moderate and strong ground motions. To mitigate the risk posed by hazardous structures, building officials and owners are finding the rehabilitation of structures a reasonable way to provide safety to building occupants and to protect their investments. One of the solutions for rehabilitation of concrete frame buildings is concrete jacketing of the structural elements. Jacketing is the addition of a concrete shell surrounding a member which is reinforced to improve the strength and ductility of the element. However, little experimental evidence is available on the performance of jacketed elements. Structural engineers have expressed interest on the behavior of beam-column joints rehabilitated by jacketing and the development of design guidelines for this scheme which are currently unavailable.; An experimental research program was implemented at The University of Texas at Austin to assess the effectiveness of jacketing of frame elements and to develop some guidelines for its design. The program was aimed at studying the behavior of beam-column-slab joints rehabilitated by jacketing. Four large-scale reinforced concrete frame connections were built to represent a prototype structure designed in the 1950's (not detailed for ductile behavior), which consisted of a joint with weak columns and strong beams. Identical existing structures were rehabilitated by jacketing the columns only, and both the columns and beams. The specimen condition prior to rehabilitation (damaged or undamaged), and the layout of the longitudinal reinforcement in the column jacket were varied. The structures were tested applying a bidirectional cyclic loading history.; Jacketing of frame elements was effective for rehabilitation of existing structures, either damaged or undamaged prior to jacketing. Analysis of test results led to the identification of the effect on performance of a damaged column prior to rehabilitation, the arrangement of the longitudinal reinforcement in the column jacket, and the jacketing of both beams and columns. The slab participation in beam negative bending was assessed. Current design recommendations for joint shear strength can be used to design well-confined interior joints rehabilitated by jacketing.