UHPC-NC键槽界面抗剪性能研究

为明晰超高性能混凝土（UHPC）加固RC结构的界面剪切力学行为，批量开展键槽定量化处理UHPC-NC界面抗剪承载性能试验研究。设计制作8组包含不同深度（t）、宽度（w）和间距（d）的UHPC-NC组合构件，分析了界面剪切荷载-滑移曲线特征，剪切应变分布规律、破坏形态以及极限抗剪承载力。试验结果表明，键槽处理方式能显著增强UHPC-NC界面初始剪切刚度（刚度值高于250 kN·mm^-1）并有效提高界面极限抗剪强度（1.46~3.98 MPa，其中大于3 MPa的试件占总数的57.1%）。不同键槽参数t，d和w对UHPC-NC界面抗剪强度的影响权值逐渐递减，且正角度开槽对界面抗剪强度的提升幅度为13%~32%，普遍优于负角度组；当深度t较小且w/t≤2时，后浇UHPC键槽部分承受较大剪切荷载，此时UHPC-NC界面出现“混合剪”破坏模式，能够有效发挥UHPC的抗弯拉性能；相同条件下，当w/t≥4时，后浇UHPC键槽面积在界面处占比增大，致使裂缝移至NC侧发展，即由NC主要承担界面剪力。此外，增大键槽间距d可改善界面域的剪力分配，“密集开槽”方式虽能有效提高界面抗剪能力，但考虑到此方式对原结构的损伤较大且施工成本较高，应对开槽深度和间距进行合理优化。提出基于断裂面法的UHPC-NC界面抗剪承载力计算公式，计算误差均在17%以内，计算结果表明，提出的公式可较好地评价定量化键槽处理的UHPC-NC界面抗剪性能。

Shear Performance of Keyway Interface Between UHPC and Normal Concrete

An experimental study on the shear bearing performance of ultrahigh performance concrete (UHPC)-normal concrete (NC) (UHPC-NC) interfaces with quantitative treatment of keyways was conducted to examine the interfacial shear mechanical behaviors of reinforced concrete (RC) structures strengthened with UHPC. Eight groups of UHPC-NC composite members with different depths (t), widths (w), and spacings (d) were designed, and the shear load-slip curve, shear strain distribution, failure mode, and ultimate shear bearing capacity of the interfaces were analyzed. The results show that keyway treatment significantly improves the initial shear stiffness (> 250 kN·mm^-1) and ultimate shear strength (1.46-3.98 MPa, 57.1% exceeding 3 MPa) of UHPC-NC interfaces. The effects of t, d, and w, on the shear strength of UHPC-NC interfaces decrease gradually. The enhancement of the interfacial shear strength, owing to the keyway with a positive angle, ranges from 13% to 32% and are generally superior to those with a negative angle. When t is small and w/t ≤ 2, a large amount of shear load is resisted by the postcast UHPC keyways, and a mixed shear failure mode of UHPC-NC specimens is observed, effectively exerting bending and tensile resistance of the UHPC. Under similar conditions, when w/t ≥ 4, the area proportion of postcast UHPC keyways at the interface increases, resulting in the development of most interface cracks on the NC side, and the shear forces are mainly resisted by the NC structure. The interface shear distribution can be improved by increasing the keyway spacing d. Although the intensive slotting method can enhance the shear resistance of UHPC-NC interfaces, the combination of the depth and spacing of the keyway should be optimized, considering the damage to the original structure and construction costs. The calculation errors obtained using the fracture surface method are within 17%, and the results indicate that the proposed method is suitable for evaluating the shear capacity of UHPC-NC interfaces with quantitative treatment of the keyways.