Study on reinforcement methods for enforcrment of sbear strengrh and improvement of ductility ofoiers made of reinforced concrete

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There occured many collapes of reiforcd concrete (RC) stru in the 1994 Far-Off Sanniku and the 1995 Hyougoken-Nanbu Earthquakes.To protect people inside of structures and keep their least functions, it is requested that RC structures shall maintain sbear resistance ststaining their shapes and the minimum residual strength even against seismic force more than the design load.These structures shall be able to use emergency after after temporary repair. This study aims enforcement of shear strength and improvement of ductility, of columns mainly in RC structures, to reply the above-mentioned.To compare the effect of different reinforcements and to devise rational arrangements, reinforced models of circular (phi150mm, h300mm), square (133 x 133mm, h 300mm) and rectangular (188 x 98mm, h 300mm) columns are prepared for compression test.Their specified strength of concrete is 280kgf/cm^2 and W/C is 55%.The diameters of main and hoop bars are 6mm and 3mm As results, aithough the maximum loads and residual sltenhths of the models are the stronger, the more hoop bars, each strength goes down suddenly after the maximym load.But in case of the rectangular columm, hoop bars are less effectixe and spiral arrangement is better.The stirrup shall be firmly connected with main axial bars.The double bar cage shows excellant behavior of the strength after the maximum load and the residual strength.Diagonal arrangement and a group of axial bars are also effective. Is is concluded that the reinforcement to shear force shall be firmly connected within square surrounding the main axial bars and a double cage or a group of axial bars prefabricated, shall be effective and economical at site.