Ductility Improvement of Pre-cast Concrete Members by Intensive Shear reinforcement

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The deformability of PCa columns in which the splicing sleeve joints concentrate in the hinge region possibly degrade, when the large amount of main bar would be arranged and the shear stress level and the bond stress level would increase. When the bond resistance in the splicing region couldn't be expected, the bond length of the longitudinal bars would be reduced. Then, the chance of bond splitting failure would increase and it would become difficult to assure the deformability. The dowel action of the rigid splicing sleeve would accelerate the bond splitting failure. This would be a serious problem in the design of PCa column members.The loading test of Pca columns was carried out where the strain on the longitudinal bar and splicing sleeve was measured in detail. Even before the yielding of main bar, the maximum strain possibly appeared at the top end of the sleeve but the bottom end because of large rigidity of splicing sleeve. Eventually it was proved that the bonding length of m … More ain bar would be reduced. The intensive shear reinforcement (ISR) would improve the bond splitting capacity as well as shear capacity, and it could improve the ductility. The loading test was conducted on the specimens with ISR which were designed to have bond splitting failure mode, and the increase of bond splitting capacity by ISR was discussed. As a result, the bond capacity increased in proportion to the amount of ISR. The contribution of ISR to the bond splitting capacity was 0.2 to 0.4% of shear reinforcement ratio. However, it was smaller than that of the ordinarily arranged shear reinforcement, which was equivalent to the amount of ISR.A half or one-third scaled specimen of Pca column with mortar grouted sleeve joints was designed. As was expected, a heavy reinforcement was required. Then 25% of the amount of required shear reinforcement was replaced by ISR. As a result of experiment, it showed a satisfactory ductility that was not different from the specimen with full ordinary shear reinforcement.The amount of main bar, that mean shear stress level, and the magnitude of axial force ware limited in a small range because of the capacity of testing facility. More experimental verification should be done in future changing the shear stress level and the axial load level, and ISR should be utilized to give the additional ductility to PCa columns together with the ordinary shear reinforcement. Less