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

在工厂生产预制钢筋混凝土构件时，由于运输过程中的冲击荷载和混凝土收缩而产生的裂缝是经常发生的。作者试图通过对PC筋等钢筋施加预应力来防止这些裂缝的发生。从一些基础试验的结果可以看出，在杆件中施加预应力，不仅可以得到开裂较少的钢筋混凝土构件，而且还可以获得部分预应力的PC构件。进一步的试验结果表明：(1)当使用SD30时，预应力达到屈服点的60%以上，就可以得到部分预应力PC构件；(2)几年后，初始预应力只有30%左右留在杆件中。明确了预制构件端部作为预应力筋的钢筋与混凝土之间的传递粘结机理，并证实了即使抗压强度低于200kgf/cm^2，预应力筋也可以锚固在端部。

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.