Reinforced concrete beams under cyclic loads

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Rad, Taghi
Department of Civil and Mining Engineering
thesis / dissertation description
An experimental and analytical study program was carried out to investigate the behaviour of reinforced concrete beams subjected to cyclic loadings which incorporated a softening region. The study focused on vibrational characteristics of which softening is the post-elastic behaviour of the critical region in reinforced concrete members which takes place simultaneously at advanced curvature and decreasing moment capacity. Cyclic loadings resulting from earthquake motions include repeated or reversed loads; however, this investigation was restricted to repeated loadings.The analytical behaviour of dynamic elements was conceived with the use of slope-deflection method (Kolousek, 1938); and the advantages of the frequency functions made possible to evaluate natural frequency, deflection due to a dynamic load, dynamic shear force and normal force. In addition to analytical phase, the response of the specimen was analysed using high-quality computer software program, ALGOR. The program is based on Finite Element method in which a continuum structure is modelled by an assemblage of discrete elements connected by a set of points called nodes.In experimental program, dynamic tests on reinforced concrete beams were conducted using small scale model. A small scale model approach facilitates in view of economy both in fabrication and testing, particularly in the dynamic structural systems. Materials used for small scale model was micro-concrete which consists of sand and cement. The specimens were constructed with the varying amounts of top and bottom reinforcement and ties around main bars. The specimens were instrumented applying modal testing which is an efficient tool for dynamic structural testing. The modal testing method was aided to observe and record the softening effect on dynamic responses. In addition, photoelasticity study were employed to observe strain patterns subjected to dynamic working loads, and the measurements were proven to be useful for the study of surface stresses of the beam critical region.The aim of the research was the correlation of measured data from structural dynamic testing with results computed by analytical methods. The general beam behaviour calculated from analysis agreed well with experimental results. The effects of softening characteristics on the responses were emphasised.