Investigation on The Restraining Method of Crack Propagation of Precast RC Members By Pretensioning Reinforcing Bars as PC Tendons

在工厂预制混凝土构件时，由于运输过程中的冲击荷载和混凝土的收缩，经常会产生裂缝。作者试图通过预应力钢筋（如PC筋）来防止这些裂缝的发生。从一些基本试验的结果可以看出，在钢筋中施加预应力，不仅可以得到裂缝较小的钢筋混凝土构件，而且可以得到部分预应力PC构件。（1）当采用SD 30时，预应力筋的预应力值大于屈服点的60%，就可以得到部分预应力混凝土构件。（2）预应力筋在使用几年后，预应力筋中只剩下约30%的初始预应力。但能显著抑制裂纹宽度的发展。（3）明确了预应力筋与预制构件端部混凝土之间的传递粘结机理，证实了预应力筋在端部即使抗压强度低于200 kgf/cm ^2也能锚固。

When a precast RC member is fabricated in a factory, the cracks due to the impact load during transportation and the shrinkage of concrete occur very often. The authors tried to prevent the occurrence of these cracks by prestressing the reinforcing bars like PC tendons. From the results of some basic experiments, it has been made clear that by applying prestressing force in bars, not only the less cracking RC members but also the partially prestressed PC members can be obtained.Further experiments were carried out and the following results were obtained :(1)The partially prestressed PC members can be got by prestressing the bars up to a value larger than 60% of the yield point when SD30 is used(2)Only about 30% of initial prestressing force remains in the bars after a few years, but it can considerably restrain the development of the crack width.(3)The mechanism of transfer bond between reinforcing bars used as prestressing tendons and concrete at the end parts of precast members has been made clear and it's also confirmed that the prestressed bars can be anchored at the end parts, even the compressive strength is lower than 200 kgf/cm^2.