Shear Behavior of Continous Reinforced Concrete Haunched Subjected To Cyclic Loading

Abstract eng:
Reinforced concrete haunched beams (RCHBs) are structural elements commonly used in buildings and bridges in Mexico and other countries worldwide. For example, in Mexico City there are several midrise buildings with RCHBs (old and recent). It is well known that the shear behavior of RCHBs is quite different from prismatic ones. Nevertheless, Mexican and United States codes do not include specific guides to design them. Based upon previous experimental research studies based upon static and cyclic testing of simply-supported RCHBs deficient in shear, the authors have proposed accurate enough methods to design RCHBs in shear supported by: a) the section approach and, b) strut-and-tie (truss model) approach. However, it is also well known from theory that the contribution of the longitudinal inclined reinforcement of RCHBs in resisting shear is different for a simply supported condition with respect to a continuity condition. To the authors´ knowledge, there are no experimental data available about the cyclic behavior of RC haunched beams deficient in shear tested under a continuity condition. Therefore, in this paper the research results and interpretations of the testing of four prototype continuous reinforced concrete beams (three haunched and one prismatic) designed to develop a shear failure under cyclic loading are presented. Subject beams were tested with minimum shear reinforcement. The studied haunched length is one-third the effective span of the beam. The considered angles of slope of haunch from horizontal vary from 00 (prismatic) to 80. Cyclic tests were displacement-controlled, and two cycles at the same displacement were set in the displacement history which considers a geometrical increment of target displacements. The parameters under study with respect to the shear-resisting mechanism are: (a) the angle of haunch from horizontal and its impact on the concrete strength, (b) the contribution of the inclined longitudinal steel reinforcement and, (c) the contribution of the transverse steel reinforcement. Differences in the cyclic shear behavior of haunched beams with respect to prismatic beams were monitored. Previously proposed design equations were examined, and it was confirmed that these equations allows to reasonably assessing their shear strength for design purposes. The obtained results from the cyclic testing in continuity conditions allow one to corroborate what it was observed in previous testing for simply supported beams: reinforced concrete haunched beams are more efficient than reinforced concrete prismatic beams, even when they fail in shear.

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