DETERMINATION OF INTERFACIAL LOCAL FRACTURE ENERGY AT STEEL BAR-CONCRETE INTERFACE
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摘要: 钢筋与混凝土界面断裂能是一个重要的参数,其决定界面的粘结滑移大小及界面发生粘结破坏后裂缝的扩展程度。以往确定钢筋与混凝土界面粘结滑移本构关系的试验中,测得的滑移量过大,使得得到的界面断裂能值偏高,与实际情况不符。但通过现有的试验手段很难较为准确地得到界面局部粘结滑移本构关系。鉴于此,该文采用理论与试验相结合的方法确定钢筋与混凝土粘结界面局部断裂能的大小。针对直径为18 mm的光圆钢筋与混凝土粘结锚固试件,利用PVC管设置不同非粘结段长度作为界面的初始缝长。通过钢筋从混凝土中的拔出试验测得不同初始缝长对应的钢筋极限抗拔力。利用界面的变形协调条件和力的平衡条件,得到了不同加载阶段钢筋拉应力与界面粘结应力沿粘结长度方向的分布表达式,进而求得钢筋的极限抗拔力。结果表明,该极限抗拔力大小取决于界面的粘结强度、残余摩擦应力和初始裂缝尖端区域的局部断裂能大小。通过钢筋极限抗拔力的理论与试验结果的比较,得到了界面局部断裂能与界面初始缝长之间的关系。进而确定了局部断裂能沿钢筋粘结长度方向的分布模型,并得到了无尺寸效应的界面断裂能大小为25 N/m。
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关键词:
- 钢筋 /
- 混凝土 /
- 界面局部断裂能 /
- 无尺寸效应的界面断裂能 /
- 极限抗拔力
Abstract: Interfacial fracture energy at the steel bar-concrete interface is a very important parameter which affects the value of interfacial shear-slip and the interfacial crack propagation after debonding. In previous tests of interfacial shear stress-slip relationship between the steel bar and concrete, the measured value of shear-slip is overestimated, resulting in the overestimation of the interfacial fracture energy. However, the actual local shear stress-slip relationship can be hardly obtained based on the present test approaches. The intention of this paper is to determine the local interfacial fracture energy between steel bar and concrete by combing the analytical model with test results. For the round plain steel bars with diameters of 18 mm anchored in concrete anchorage specimens, PVC tube was used to determine different unbonded lengths denoted as the initial crack lengths. Then the maximum pull-out load of steel bar from concrete can be experimentally measured. The distributions of tensile stress in the bar and interfacial shear stress along the bonding length were expressed in closed form at different loading stages based on the deformation compatibility conditions at the interface and equilibrium conditions of forces. Thus, the maximum pull-out load can be given analytically. The results show that the analytically determined maximum pull-out load is related to the bonding strength, residual frictional stress and local fracture energy at the crack-tip region. The correlation between the crack-tip local fracture energy and initial crack length is established upon the comparison between the analytically determined maximum pull-out loads and the experimentally measured ones. The interfacial local fracture energy distribution along the bonding length is then given, and the size-independent interfacial fracture energy is 25 N/m. -
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