Retrofit of nonductile reinforced concrete frames using high performance fiber-reinforced composites.

摘要

Many older reinforced concrete frame structures built in the United States are non-ductile and are thus identified as hazardous. The main goal of this project was to develop a technique for seismic retrofit of such structures using High Performance Fiber Reinforced Cement Composites, i.e., Slurry Infiltrated Fiber Concrete (SIFCON) and Slurry Infiltrated Mat Concrete (SIMCON). In addition to a weak - column strong - beam type of response, these frames have: (1) insufficiently confined column lapped splices, (2) discontinuous beam-bottom reinforcement, and (3) little or no joint reinforcement. HPFRCCs exhibit high strength, high toughness, excellent crack control, and superior energy absorption and are thus ideally suited for seismic retrofit.;The project consisted of two phases in which: (1) discontinuous column SIMCON-jacketing and "internal" joint retrofit with prestressing bars, and (2) continuous column and joint SIMCON-jacketing and partial replacement of concrete with SIFCON, were investigated. To minimize the number of variables, continuous beam bottom reinforcement was used in the first phase while discontinuous reinforcement was used in the second phase. Two reference and one retrofitted specimens were tested in the first phase, while one reference and one retrofitted specimen were tested in the second phase. Discontinuous SIMCON jacketing used in the first phase eliminated deterioration and failure of column lap splices, while placement of high strength reinforcement through the joint slowed down crack propagation and limited crack opening. The result was markedly increased ductility, energy absorption, and a more stable specimen response at higher story drifts. Continuous column and joint SIMCON jacket used in the second phase prevented lap splice failure, increased strength, ductility and energy absorption of the specimen. Replacement of concrete in the anchorage zone of the beam-bottom reinforcement with SIFCON eliminated reinforcement pull-out failure. The weak column - strong beam response was prevented, and the retrofitted specimen exhibited a stable beam sidesway mechanism.;Retrofit design guidelines for the design of the HPFRC-based retrofit schemes were presented. The design procedure presented herein seems to be appropriate for the tested specimens, while more testing as well as analytical work is needed to fully confirm the proposed design approach.