超高性能混凝土-螺旋钢纤维拉拔力的解析解及实验验证

Analytical solution and experimental verification of pullout force of twisted steel fibers in ultra–high performance concrete

为了研究螺旋钢纤维增强超高性能混凝土(UHPC)的破坏力学机理,开展不同埋长的纤维单根拉拔实验,得到拉拔力-位移全过程曲线,采用微观X光断层扫描(XCT)对拉拔前、后的基体变形进行观测.实验结果显示,矩形截面螺旋钢纤维拉拔过程分为近似线性脱黏段、塑性解螺旋段和骤降段,可以简化为三折线;XCT图像显示拉拔前、后UHPC基体通道未见明显破坏,揭示了螺旋钢纤维单根拉拔过程的"解螺旋"塑性变形机理;只要纤维埋长大于有效解螺旋长度,则解螺旋段的拉拔力与埋长无关.基于以上实验现象和塑性力学理论,推导了矩形截面钢纤维解螺旋拉拔力的简化解析解公式,与实验结果吻合良好.

The pullout force-displacement curves during the whole process were obtained by conducting pullout tests with a single fiber with different embedment length in order to analyze the damage mechanism of twisted steel fiber reinforced ultra-high performance concrete(UHPC).The micro X-ray computed tomography(XCT)scanning was conducted to analyze the deformation of the UHPC matrix before and after the fiber was pulled out.The test results show that the pullout curves can be simplified as a trilinear model consisting of an approximatively linear stage,a plastic“untwisting”stage and a sudden dropping stage.The micro-XCT images showed no evident damage in the fiber-UHPC channel after the fiber was pulled out,revealing the untwisting plasticity deformation mechanism special to the twisted steel fiber reinforced UHPC.The untwisting pullout force was independent of fibre embedment length as long as it was longer than an effective untwisting length.A simplified analytical solution for the untwisting pullout force was derived for fibres of rectangular section based on the experimental results and the plasticity theory.The solution agreed well with the experimental results.