UBC Theses and Dissertations
Retrofitting beam-to-column joints for improved seismic performance microform Hoffschild, Thomas E.
Before the 1970's, most codes for the design of reinforced concrete structures did not include provisions for ductility during seismic events was not prevalent in most codes. The guidelines that did exist were minimal, and often left a fair amount of room for interpretation by the design engineer. Hence, many of the reinforced concrete structures designed during that time are suspect under today's more stringent design guidelines. Moreover, even the present designs are often deficient and vary from building to building and from jurisdiction to jurisdiction. This report is a presentation of the findings of an experimental study to evaluate a method of retrofit which addresses a particular weakness that is often found in reinforced concrete structures, namely the lack of sufficient reinforcement in and around beam-to-column joints. Many of these structures lack the required confining reinforcement within the joints and in adjoining beams and columns. The result is a reinforced concrete framethat is weak in the joint area and lacks sufficient ductility during a seismic event. The proposed retrofit method consists of encasing the reinforced concrete joint with a grouted steel jacket that provides confinement to the joint area, and imparts ductility to the frame. In this study, two styles of retrofit jacket were tested: a circular steel tube and a rectangular casing. It was found that circular steel jackets have the advantage of providing direct concrete confinement and, as well, of furnishing a ductile force transfer mechanism through the jacket itself, but are also more difficult and expensive to fabricate than rectangular jackets. Although rectangular jackets do not provide the same degree of concrete core confinement as circular jackets, the amount available seems sufficient to prevent damage in the joint area. The load transfer mechanism of the rectangular jackets was found to be adequate in withstanding the loads and deflections typical for seismic events. In this thesis, the two jacket styles are evaluated for strength, stiffness and ductility, and their relative merits are discussed.
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