Study on Impact Tensile Strength of Concrete and Impact Falure of Reinforced Concrete Members

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(1) A newly developed measuring method for impact tensile strength of concrete has been proposed. The measurement method is based on the superposition and concentration of tensile stress waves reflected both from the free ends of a striking bar and a specimen bar. The impact tensile experiment is conducted by means of an air gun arrangement and a stress-bar technique. The setup consists of a striking bar shot out from an air gun and an input bar colliding collinearly with the striking bar on its one end. Another end of the input bar is in tight contact with one end of a specimen bar.(2) The measuring theory and the impact breaking behavior of concrete specimens were discussed on the base of the simple theory of stress waves propagated in a bar. They were verified by not only the experimental measurement but also the numerical simulation in axsymmertrical two demensional analysis using FEM code MARC.Reasonable agreements between the experimental measurement and calculated results were obtained.(3) The impact tensile experiment of some kinds of concrete specimens was performed, together with static strength tests such as direct tension, splitting tension, bending, and compression tests. The breaking position in a concrete specimen bar almost corresponded to the predicted position at which tensile stress concentration was initiated. It was found from the statistical analyses of the experimental data that the impact tensile strength of concretes was significantly influenced by loading-rates, and was found to be more than twice the static value.