预制混凝土梁湿接缝环形钢筋搭接长度研究

Research on the Overlap Length of Looped Bars in Cast-in-place Joint for Precast Concrete Girder Systems

分析了一般钢筋搭接和环形钢筋搭接的传力机理,指出环形钢筋搭接的实质为环形钢筋通过搭接段钢筋间核心混凝土柱自锁锚固,通过核心混凝土柱抗剪而非钢筋与混凝土的黏结作用平衡搭接钢筋拉力,与PBL键通过孔间混凝土柱抗剪承载的机理类似。借鉴PBL键单孔承载力计算经验数据,以单剪切面核心混凝土柱抗剪承载力与环形钢筋抗拉承载力等强为控制条件,建立了环形钢筋搭接的长度计算公式。算例表明,核心混凝土截面足够时,环形钢筋搭接长度受钢筋直线段最小间距为零的构造要求控制,搭接承载力与搭接区钢筋采用绑扎或焊接等连接形式无关。试验证明,对于常用厚度的装配式预制梁湿接缝,建议的公式是合理的,并具有工程所需的精度。

The mechahisms of overlap connection of normal steel bar and looped bars are analyzed in the paper, and it is push forward that overlap connection of looped bars relies on the self-lock by the core concrete in the overlap region. The tension forces of looped bars are balanced by the shear force of core concrete instead of the bond strength between concrete and bars, which is similar to the mechanism of PBL shear connector. The formula of overlap length of looped bars is established by the condition that shear capacity of core concrete and tension capacity are equal, and some practical data from PBL shear connector research result is referred. It is found by the numerical example that overlap length of looped bars is controlled by the minimum overlap length of more than zero between two straight parts of looped bars if the capacity of core concrete is enough, neither welding nor bounding between two looped bras affects the overlap bearing capacity. It is proved by the model experimental tests that the suggested formula is reasonable for the normal thickness of cast-in-place （CIP） joint used in precast concrete girder systems and is accurate enough for engineering purpose.