单向受拉状态下钢纤维混凝土的二次峰值强度

不同于普通混凝土在单向受拉实验中的仅有唯一峰值强度，在大量钢纤维混凝土拉伸实验的应力应变曲线中均出现了两次峰值强度现象。本文采用黏结滑移模型考虑纤维在混凝土开裂面上的桥接作用，确定了钢纤维轴向应力与裂缝宽度之间的关系。钢纤维混凝土开裂后，将基体的软化模量与纤维增强作用的切线模量之和，作为判断第二峰值的依据。该值始终为非负时，钢纤维混凝土的应力-应变曲线具有唯一峰值强度；否则，应力-应变曲线中将具有二次峰值强度，并提出了钢纤维混凝土峰值强度的三种可能情况。建立了有限元模型以模拟钢纤维混凝土的拉伸试验，进一步研究了钢纤维掺量、长径比对混凝土开裂后力学性能的影响。并提出了钢纤维混凝土的抗拉强度的计算公式，可以有效地预测钢纤维混凝土的抗拉强度。

Second peak strength of steel fiber reinforced concrete under uniaxial tension

In uniaxial tensile tests,steel fiber reinforced concrete(SFRC)manifests two tensile strength peaks in the stress-strain curves,a phenomenon already revealed in a number of observations and different from the plain concrete case of a single strength peak.This study considers the effect of fibers bridging a crack using the bond-slip model for the interaction between the fibers and matrix,and formulates a relationship of steel fiber reinforcement stress versus crack width.The sum of the softening modulus of the matrix and the reinforcement modulus of the fiber is used for judging the occurrence of the second peak.When the sum is always non-negative,the SFRC stress-strain curve has a unique stress peak;otherwise,this curve will have two tensile strength peaks.Hence,we suggest three peak strength cases for SFRC,construct a finite element model to simulate its tensile tests,and examine the effects of fiber contents and fiber aspect ratios on its mechanical properties under the occurrence of concrete cracking.A calculation formula for the tensile strength of SFRC is given,which shows effective predictions.