Buckling and Rupture of Main Reinforcement Related to Ultimate Limit of Concrete Flexural Members

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Investigations to make clear effects of confined concrete on buckling strains of longitudinal reinforcement under uniaxial monotonical loading and cyclic loading were carried out.On the case of cyclic loading, to measure stress of longitudinal reinforce-ment, a new type load cell (a rebar load cell), which was quench hardened portions located locally along the reinforcement, was used.Rupture of reinforcement could not be investigated owing to lack of time.Following main conclusions are obtained.1. Equations to estimate buckling strains of compressive longitudinal reinforcement arranged in confined concrete are derived, through discussions on results of our experimental studies.In the tests of confined concrete with longitudinal reinforcement under uniaxial compressive loading, effects of following factors on the buckling strains were investigated, such as ratios of lateral reinforcement pitches to specimen diameters (S/D), an index of confining stress (ps siguma sy), yield strength of the lateral reinforcement (siguma sy), shapes of lateral reinforcement, compressive strength of plain concrete (Fo), diameters of longitudinal reinforcement (phi) and locations of longitudinal reinforcement.Comparisons between test results of buckling strains and estimated ones show that the derived equation has successful applicability about * 30 %.2. Re-bar load cells could derive stress-strain relations over yielding region of reinforcement arranged in confined concrete under cyclic loading.3. Cyclic loading tests indicate that prediction of buckling strains may be feasible using skeleton curves obtained from the measured stress-strain curves, and stress-strain relations of confined concrete surrounding reinforcement.