中文摘要：

为提高超高性能混凝土（UHPC）的初裂应变，在基体中混合掺入平直钢纤维和端钩钢纤维，考虑纤维掺量和形状的影响，对掺混合纤维的UHPC进行了轴拉试验。采用控制变量法，将4种含不同纤维掺量的UHPC材料的轴拉特征参数进行了对比分析。基于实测曲线，提出了包含应力一应变关系和应力一裂缝宽度关系的两阶段拉伸本构模型。研究结果表明：不同纤维掺量的UH—PC材料的拉应力一伸长曲线随多元开裂均呈明显的应变硬化特性；当钢纤维掺量由2％增至3．5％时，可视初裂应变增加201％，且端钩纤维的增强效率为平直纤维的3．52倍；含3．5％纤维掺量的UHPC材料的可视初裂应变和极限应变分别高达1．777×101和1．941×10-3^，均与普通钢筋屈服应变（2×101）接近，可视初裂前UHPC材料能与钢筋协同变形；UHPC受拉本构关系模型与试验数据均符合较好。

英文摘要：

To enhance the crack-observed strain of Ultra High Performance Concrete （UHPC）, hybrid steel fibers including straight fibers and hooked-end fibers were blended into the matrix of UHPCs. Considering the influence of fiber content and fiber shape, axial tensile test of UHPC with hybrid fibers was investigated. With control variable method, axial tensile characteristic parameters of UHPCs with four different fiber contents were compared. Based on measured tensile stress-elongation curves, a two-stage tensile constitutive model of UHPC comprised of a stress-strain response and a stress-crack opening relationship was proposed. The results show that tensile stress-elongation curves of UHPC with different hybrid fiber contents apparently exhibit strain-hardening behavior with multiple cracking. As the fiber content increases from 2 to 3. 5%, the crack-observed strain considerably improves by 201% and the enhancement of hooked-end fibers is 3.52 times greater than that of the straight fibers. With addition of 3.5 hybrid fibers by volume, the strains, corresponding to the observed cracking and stress softening, are 1. 777× 10-3^ and 1. 941 X 10-3^ respectively, which approach the yielding strain of common reinforcing bar （2 × 10-3^）. coordinately deform with reinforcing stee proposed UHPC tensile constitutive mod Before an occurrence of a visible crack, UHPC can 1. Finally, test data are satisfactorily approximate to the