钢绞线混凝土黏结性能试验与锚固长度分析

Experimental analysis of bond property and anchorage length for strands

为研究较大直径钢绞线与混凝土间的黏结锚固问题并提出合理锚固长度,针对15.2、17.8、21.6mm三类公称直径的高强低松弛钢绞线,以混凝土保护层厚度、体积配箍率及埋置长度为基本参数,完成了32个钢绞线的中心及偏心拔出试验.试验结果表明,不同参数水平条件下拉拔试件的破坏可分为两类,一是较薄保护层厚度与较小体积配箍率的少量试件劈裂破坏;二是在绝大部分试件中出现的表面未开裂但钢绞线拔出的破坏.结合破坏特征及拉拔力-滑移关系曲线,揭示了钢绞线混凝土间的黏结破坏机制,并以拉拔力-滑移曲线的峰值为破坏标志,提出了分别考虑3个参数影响的钢绞线混凝土黏结强度计算方法;结合本文试验结果,引入近似概率法,确定了满足相应可靠指标要求的钢绞线锚固长度设计值,可为装配式公共建筑结构中采用的大型先张预制预应力混凝土构件的设计提供技术支持.

To investigate the bond between the concrete and the large-diameter strands and reasonably propose design development lengths, pull-out tests of 32 specimens with strands arranged centrically and eccentrically were carried out. The test focused on high-strength and low-relaxation strands of nominal diameters of 15.2 ram, 17.8 ram, and 21.6 ram. Main parameters included the thickness of the concrete cover, the volumetric stirrup ratio, and the anchoring length. The test results show that the pull-out specimens had two failm~ modes, though testing parameters varied for different specimens. The first mode was concrete splitting failure for a few specimens having both thin cover and small volumetric stirrup ratio, and the other was apparent pull-out of strand for most specimens but no cracking was observed. Based on the failure characteristics and the relationship between the pull-out force and slip, the mechanism of bond failure between strands and concrete was presented. The peak point of the pull-out curve was taken as the sign of failure. A calculation method for the bond strength between strand and concrete was proposed considering the effects of three parameters. The approximate probabilistic method was adopted to analyze the design value of the development length of the strands to meet the requirements of the corresponding reliability index. It can serve for the design and analysis of large-span pre-tensioned concrete members applied in precast structures of public buildings.