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

当主筋数量较多，剪应力水平和粘结应力水平增大时，套筒节点集中在铰区的PCa柱的变形能力可能降低。当搭接区的粘结阻力不能达到预期值时，纵向钢筋的粘结长度将减小。这样，粘结开裂失效的机会将增加，并且将难以保证变形能力。刚性连接套管的传力作用会加速接头的劈裂破坏。本文对预应力混凝土柱进行了荷载试验，详细测量了预应力混凝土柱纵筋和搭接套管的应变。在主筋屈服前，由于拼接套管刚度大，最大应变可能出现在套管顶端，而不是底端。最终证明了m的键长 ...更多信息 则会降低增益。加强抗剪钢筋可以提高粘结劈裂承载力和抗剪承载力，并能提高延性。对设计成粘结劈裂破坏模式的ISR试件进行了加载试验，探讨了ISR对粘结劈裂承载力的提高作用。因此，债券的容量增加的ISR的数量成比例。ISR对粘结劈裂承载力的贡献为0.2%~ 0.4%。设计了1/2或1/3缩尺的砂浆套节点Pca柱试件，试验结果表明，砂浆套节点Pca柱的抗剪承载力比普通抗剪承载力小，与普通抗剪承载力相当。正如预期的那样，需要大量增援。然后用ISR代替所需抗剪钢筋量的25%。试验结果表明，该试件具有良好的延性，与普通钢筋混凝土试件无明显差别，但由于试验设备的限制，主筋数量、平均剪应力水平和轴力大小均在较小范围内。今后还需要进一步的试验验证，改变剪应力水平和轴力水平，并在普通抗剪钢筋的基础上，利用ISR来提高PCa柱的延性。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