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摘要: 为促进超高性能混凝土(UHPC)深梁的应用, 进行了4根以混凝土强度为主要参数的UHPC深梁受剪性能试验, 并开展了C40和C80混凝土深梁的对比试验; 分析了UHPC深梁的荷载-挠度曲线、破坏模式、钢筋应变、裂缝形态与极限荷载; 为探讨现有普通混凝土深梁受剪承载力计算方法是否可用于UHPC深梁, 应用《混凝土结构设计规范》(GB 50010—2010)对6根深梁试件进行了抗剪强度计算。研究结果表明: 混凝土强度越大, 在相同荷载下深梁的刚度越大, 在深梁开裂前的弹性阶段, UHPC试件刚度随钢纤维掺量的增大略有增大; 与C40和C80混凝土深梁一样, UHPC深梁裂缝包括弯剪裂缝和腹剪裂缝, 当荷载分别为13%~22%和18%~34%极限荷载时, 两类裂缝先后出现; UHPC深梁在加载全过程中梁、拱受力机制共存, 加载前期梁受力机制起主导作用, 后期则拱受力机制起主导作用; UHPC深梁裂缝多而密, 发生剪压破坏, 在支座上端反拱区不产生裂缝, 而C40和C80混凝土深梁出现斜压破坏, 且在支座上端反拱区产生裂缝; 试验梁受剪承载力随混凝土强度的增大约呈指数式增大, 混凝土强度从C40增大到C80、C190时, 其受剪承载力分别增大了30.76%和201.92%;采用《混凝土结构设计规范》(GB 50010—2010)中方法计算的UHPC深梁受剪承载力与试验值比值的均值为0.89, 均方差为0.15, 在没有更精确的计算方法之前, 该计算方法暂时可用。Abstract: To promote the application of ultra-high performance concrete(UHPC) deep beams, shear performance tests were conducted on four UHPC deep beams by taking the concrete strength as the main parameter, and the C40 and C80 concrete deep beams were tested for comparison. The load-deflection curves, failure modes, reinforcement strains, crack patterns and ultimate loads of UHPC deep beams were analyzed. The method specified in the Code for Design of Concrete Structures(GB 50010—2010) was used to determine the shear strengths of six deep beam specimens, to discuss whether the current method for calculating the shear capacity of ordinary concrete deep beams is applicable to UHPC deep beams. Research result shows that the greater the concrete strength is, the greater the stiffness of the deep beam under the same load is. The stiffness of UHPC specimen in its elastic stage before the cracking increases slightly with the increase of steel fiber content. Similar to the C40 and C80 concrete deep beams, the UHPC deep beams exhibit bending-shear and web-shear cracks. When the load reaches 13%-22% and 18%-34% of the ultimate load, the two types of cracks appear successively. Beam and arch stress mechanisms are both present during the loading of UHPC deep beams. The beam stress mechanism dominates the early phases of loading process, whereas the arch stress mechanism dominates the latter stages of this process. The UHPC deep beams exhibit a large number of densely and concentrated cracks and undergo shear-compression failure, without showing any cracks in the inverted arch area above their supports. In contrast, the C40 and C80 concrete deep beams undergo diagonal compression failure, and cracks appear in the inverted arch area above their supports. The shear bearing capacity of test beam increases in an approximately exponential manner with the increase of concrete strength. When the concrete strength increases from C40 to C80 and C190, the shear bearing capacity increase by 30.76% and 201.92%, respectively. When using the method specified in the Code for Design of Concrete Structures(GB 50010—2010) to calculate the shear bearing capacities of UHPC deep beams, the calculated and experimental shear bearing capacities show an average ratio of 0.89 and a mean squared error of 0.15. Therefore, this method can be temporally used to calculate the shear bearing capacity of UHPC deep beams, until a more accurate calculation method is available.
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表 1 UHPC的配合比
Table 1. Mix proportion of UHPC
材料 水泥 硅灰 石英砂 石英粉400目 减水剂 水 钢纤维/% 40~70目 20~40目 10~20目 配合比 1.00 0.30 0.14 0.41 0.53 0.09 0.03 0.21 0.5~3 表 2 UHPC力学性能
Table 2. Mechanical properties of UHPC
试件编号 v/% fc/MPa fu/MPa ft/MPa E/GPa fs/MPa L1-1 0.5 113.4 132.3 6.18 44.9 14.1 L1-2 1.0 125.6 145.5 7.19 45.6 15.1 L1-3 2.0 151.4 175.2 9.54 46.2 19.5 L1-4 3.0 173.6 198.6 13.56 47.9 26.6 L2-1 0.0 46.9 53.3 3.24 38.5 7.4 L2-2 0.0 86.5 98.3 4.23 41.7 9.8 表 3 深梁受剪承载力试验结果
Table 3. Results of shear bearing capacity tests on deep beams
试验梁 fu/kN 受剪承载力Ve/kN 增量/% 破坏形态 L2-1 53.3 466.07 斜压破坏 L2-2 98.3 609.42 30.76 斜压破坏 L1-1 132.3 873.31 87.38 剪压破坏 L1-2 145.5 1 089.40 133.74 剪压破坏 L1-3 175.2 1 356.96 191.15 剪压破坏 L1-4 198.6 1 407.18 201.92 剪压破坏 -
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