配置BFRP筋复合配筋PHC管桩受弯和受剪性能试验研究

为解决预应力混凝土(PHC)管桩水平承载力不足的技术难题，开展了配置玄武岩纤维(BFRP)筋复合配筋PHC管桩(PRC-B管桩)和配置普通钢筋的复合配筋PHC管桩(PRC管桩)受弯、受剪性能的对比试验。受弯试验结果表明：BFRP筋的配置改善了PHC管桩的承载性能；与PHC管桩相比，PRC-B管桩的开裂弯矩和极限弯矩均有显著提高，且弹性变形更小、中性轴高度更低、裂缝分布范围更短且数量更少；两种类型桩的跨中截面应变符合平截面假定，破坏时PRC-B管桩受拉区裂缝宽度超限同时受压区混凝土开裂，而PRC管桩仅受拉区裂缝宽度超限。受剪试验结果显示：配置BFRP筋较大幅度提高了PHC管桩的受剪性能，其抗裂剪力和极限剪力分别有不同程度的提高；两种类型桩破坏过程类似，均是在剪弯段先出现两条对称的斜裂缝，逐步发展至中性轴高度处，以平行于桩长方向继续发展贯通形成主贯通面，最后因主裂缝宽度超限而破坏。所提出的配置BFRP筋复合配筋预应力混凝土管桩的受弯承载力计算公式，其计算结果相对试验承载力具有合理的富余。对比试验结果表明，BFRP筋可以替代普通钢筋改善PHC管桩的承载性能。

Experimental study on flexural and shear capacity of PHC pile compositely reinforced with BFRP bars

In order to solve the technical problem of insufficient horizontal bearing capacity of pre-stressed concrete pipe pile (PHC pile), PHC pile reinforced with basalt fiber reinforced polymer (BFRP) composites bars (called PRC-B pile) was developed. The flexural and shear behavior of PRC-B piles were studied through comparative tests with PHC pile reinforced with non-prestressed steel bars (called PRC pile). The flexural test results show that BFRP bars can improve the flexural capacity evidently. Both the cracking bending moment and the ultimate bending moment of the PRC-B pile have increased to some extent. The PRC-B pile exhibits more characteristics such as smaller elastic deformation, shorter crack distribution range, less number in cracks and lower in neutral axis height. Furthermore,the strains at the midspan cross section of all the specimens conform to the assumption of plane section.Failure of PRC-B piles occurs by both exceeding the limit of crack width and cracking of the compression zone of the concrete, in comparison, PRC piles are broker by exceeding the limit of crack width.Meanwhile, the shear test results show that the shear capacity of the PHC pile can be enhanced using BFRP bars and the cracking shear force and the ultimate shear force can be improved significantly. The failure process of the two type pipe piles are similar, initiating from shear-flexure section and extending to the neutral axis, forming through plane in the direction parallel to the pile, and finally fail due to the width of the main crack exceeding the limit. Moreover, the formula for calculating the flexural capacity of PRC-B pile was proposed and the calculated results based on the formula led to reasonable agreement with the test results. The experimental results show that the flexural and shear capacity of PHC pile reinforced with BFRP bars as an alternative to non-prestressed steel bars can be improved.