UHPC构件受拉性能的细观力学解析方法

超高性能混凝土（Ultra-high-performance Concrete，UHPC）的受拉性能直接影响结构的抗裂性和耐久性，是结构设计中重要的力学指标之一。为研究UHPC构件在弯拉荷载作用下产生宏观裂缝前的受拉力学特性，以钢纤维与水泥基的协作受力特性为切入点，考虑钢纤维分布方向的随机性服从正态分布，建立了钢纤维受拉作用下的细观力学模型。该模型将钢纤维力作为由水泥基加载的被动力进行分析，在充分考虑水泥基材料特点的基础上，发展了UHPC构件受拉作用下宏观裂缝出现前弹性和拔出2个阶段的力学行为预测模型；开展了UHPC试件的纯弯曲试验，标定了材料受弯全过程中的关键力学指标，重点关注理论预测的弹性和拔出2个阶段的力学行为，并与预测模型计算结果进行对比；采用文献中钢纤维增强混凝土的试验结果进一步印证细观力学模型的适用性。理论分析及试验结果表明：建立的细观力学模型可准确描述出现宏观裂缝前受拉UHPC构件内部钢纤维的抗拉力学行为；预测模型计算的理论值与UHPC构件受拉作用下弹性和拔出2个阶段的力学指标试验结果吻合良好；常规钢纤维掺量的UHPC受拉性能由其内部钢纤维主导，理论计算时忽略受拉状态下水泥基对UHPC轴力的贡献不仅可以简化计算，而且可将其视为工程应用时的安全储备；建议的双折线拉伸本构中弹性与拔出2个阶段的极限应变分别为180×10^-6，1 042×10^-6。

Micro-mechanics Research on Tensile Mechanical Behavior of UHPC Specimen

The tensile behavior of ultra-high-performance concrete (UHPC) directly affects the crack resistance and durability of a structure. Thus, it is an important index. Based on an analysis of the cooperation between steel fiber and surrounding cement base, a mesomechanics tensile behavior model was established to study the tensile properties of a tensile UHPC structure before cracking. The random distribution of the steel fiber was considered to be the normal distribution, and the fiber force was considered to be the reactive force loaded by the cement base. A mechanical behavior prediction model was established to predict the mechanical behavior of the tensile UHPC in the elastic and pull-out stages based on the mesomechanics tensile behavior model. Pure bending specimens were tested to obtain the mechanical index, and the tensile behaviors at the elastic and pull-out stages were compared with those of the previously mentioned model. Moreover, the applicability of the mesomechanics tensile behavior model was verified using other reference data. The results showed that the working mechanism of the inner steel fiber could be described by the mesomechanics tensile behavior model before cracking. The bending test results of the UHPC at the elastic and pull-out stages agreed well with the theoretical values. The tensile behavior of the UHPC was dominated by the inner steel fiber, and the contribution of the cement base could be ignored to simplify the calculation and security. A bilinear tensile constitutive model was proposed, where the limit of the elastic stage was 180×10^-6, and the minimum test value of 1 042×10^-6 was taken as the limit of the pull-out stage.