FRACTURING TRUSS MODEL: SIZE EFFECT IN SHEAR FAILURE OF REINFORCED CONCRETE
FRACTURING TRUSS MODEL: SIZE EFFECT IN SHEAR FAILURE OF REINFORCED CONCRETE
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DOI：
10.1061/(asce)0733-9399(1997)123:12(1276
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发表时间：
1997-12
期刊：
影响因子：
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通讯作者：
Z. Bažant
中科院分区：
文献类型：
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作者：
Z. Bažant
对钢筋混凝土豆荚剪切破坏的经典桁架模型（或拉杆模型）进行了修正，以描述破坏过程中的断裂现象。这种破坏被认为是由于在达到最大荷载的加载历史期间，混凝土支柱上的压缩断裂的传播引起的。压缩断裂可以由一组劈裂裂缝组成，这些裂缝后来相互连接形成剪切裂缝或向支撑倾斜的剪切断裂带。假定断裂带的宽度仅占支撑长度的一部分，并代表与梁深无关的固定材料特性。桁架释放能量的计算采用两种近似方法：(1)利用从应力释放区概念推导出的势能变化；(2)利用断裂带在受压混凝土支撑上传播引起的应力重分布引起的互补能量变化。这两种方法都表明，尺寸效应对名义剪切破坏强度的影响一定存在，并且应该大致遵循1984年Bazant提出的尺寸效应定律。并对尺寸效应的物理机理进行了清晰直观的解释。最后，表明所施加的名义剪应力，导致大的初始对角裂纹的形成也表现出尺寸效应。
The classical truss model (or strut-and-tie model) for shear failure of reinforced concrete beans is modified to describe fracture phenomena during failure. The failure is assumed to be caused by propagation of a compression fracture across the concrete strut during the portion of the loading history in which the maximum load is reached. The compression fracture may consist of a band of splitting cracks that later interconnect to form a shear crack or a shear fracture band inclined to the strut. The width of the fracture band is assumed to occupy only a portion of the strut length and to represent a fixed material property independent of the beam depth. The energy release from the truss is calculated using two alternative approximate methods: (1) using the potential energy change deduced from the concept of stress relief zones; and (2) using the complementary energy change due to stress redistribution caused by propagation of the fracture band across the compressed concrete strut. Both approaches show that a size effect on the nominal strength of shear failure must exist and that it should approximately follow the size effect law proposed by Bazant in 1984. The physical mechanism of the size effect is also explained in a clear and simple intuitive manner. Finally, it is shown that the applied nominal shear stress that causes large initial diagonal cracks to form also exhibits a size effect.