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

当主筋布置较多，剪应力水平和粘结应力水平增大时，拼接套筒节点集中在铰接区的PCA柱的变形能力有可能降低。当拼接区的粘结阻力达不到预期时，纵筋的粘结长度会减小。这样，粘结断裂失效的几率就会增加，变形性就难以保证。刚性拼接套筒的传力作用会加速粘结劈裂破坏。这将是PCA柱构件设计中的一个严重问题。进行了PCA柱的加载试验，详细测量了纵筋和拼接套筒上的应变。即使在主筋屈服之前，由于拼接套筒的刚度较大，最大应变可能出现在套筒的顶端而不是底端。最终证明了m-…的键长更多的An门槛将会减少。强剪配筋可以提高粘结劈裂能力和抗剪能力，改善延性。对设计为具有粘结劈裂破坏模式的带ISR的试件进行了加载试验，讨论了ISR对粘结劈裂能力的提高。因此，债券容量与ISR的数量成比例增加。ISR对粘结劈裂能力的贡献为抗剪配筋率的0.2%~0.4%。但它比常规布置的剪力筋小，相当于ISR的用量。设计了一半或三分之一缩尺的砂浆灌浆套筒节点PCA柱试件。正如预期的那样，需要大量增援。然后，所需抗剪钢筋的25%被ISR取代。试验结果表明，该试件具有良好的延性，与普通剪力筋完全配筋的试件没有什么不同，但由于试验设备的限制，主筋的数量、平均剪应力水平和轴力的大小都被限制在很小的范围内。在今后改变剪应力水平和轴压水平时，应进行更多的试验验证，并应采用ISR来与普通受剪钢筋一起赋予PCA柱更多的延性。较少

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