钢纤维特性对UHPC轴拉性能与弯拉性能的影响及对比研究

为定量地研究钢纤维特征参数对超高性能混凝土（Ultra-high Performance Concrete，UHPC）受拉性能的影响规律，现对同一纤维体积掺量（2%）下不同纤维长径比（59~100）、不同纤维类型（端钩型与平直型）及无钢纤维的UHPC试件分别开展了轴拉试验与四点弯拉试验。通过选取拉伸全曲线上的初裂点、峰值点及其他几个特征点，定量地分析了UHPC拉伸过程中的轴拉性能与弯拉性能，并对2种拉伸试验下的初裂强度与峰值强度进行了对比与分析，最后利用ABAQUS软件对2种拉伸全曲线进行了有限元倒推分析。研究结果表明：①随着一定范围内的纤维长径比的增加，与轴拉试验相比，UHPC试件的拉伸强度和拉伸韧性在弯拉试验中提升得更明显；②无论是端钩型还是平直型纤维试件，轴拉应变达到3 000×10^-6时的应力均高于7 MPa，且大弯拉变形状态下的强度均仍为弯拉初裂强度的1.17~2.43倍；③有无钢纤维对UHPC轴拉性能与弯拉性能均具有不同程度的裂后增强效果，其中后者优于前者；④在UHPC结构设计中可用考虑尺寸效应修正后的弯拉初裂强度来估算轴拉初裂强度，且扣除纤维取向的影响后，基于ABAQUS有限元软件倒推输入的三折线轴拉本构与实测的轴拉本构基本相符。

Influential and Comparative Research on the Effects of Steel Fiber Properties on the Axial Tensile and Bending Tensile Properties of UHPC

To study the influence of characteristic parameters of steel fibers on the tensile properties of ultra-high performance concrete (UHPC) quantitatively, the axial tensile test and the four-point bending test were carried out on UHPC specimens at the same fiber content (2%) with different fiber l/d ratios (59-100), different fiber types (hooked-end or straight), and without steel fibers. By selecting the initial crack point, peak point, and several other characteristic points on the whole tensile curve, the axial tensile properties and bending properties of UHPC during the tensile process were analyzed quantitatively, and the initial crack strength and peak strength under the two kinds of tensile tests were compared and analyzed. Finally, finite element inverse analysis of the two kinds of whole tensile curves was implemented using ABAQUS software. The results follow: ① With increase of fiber l/d ratio within a certain range, the tensile strength and tensile toughness of UHPC specimens increase more obviously in the bending test than in the axial tensile test. ② For both hooked-end fiber and straight fiber specimens, the stress under the axial tensile test is higher than 7 MPa when the strain reaches 3 000×10^-6, and the strength under large bending deformation remains 1.17-2.43 times the initial crack bending strength. ③ The axial tensile and bending properties of UHPC with or without steel fibers have different post-crack reinforcement effects, and the latter is better than the former. ④ In the design of UHPC structures, the modified initial crack bending strength considering the size effect can be used to estimate the initial crack axial tensile strength. After deducting the influence of fiber orientation, the input tri-linear tensile constitutive model by ABAQUS finite element software is basically consistent with the measured one.