西安建筑科技大学学报(自然科学版)

混凝土抗压强度测试时压头与试块接触面之间存在摩阻力,该阻力约束了试块上下表面水平方向的位移,这种边界条件最终对真实强度产生了影响,针对这一现象,对强约束条件下立方体中的剪切带进行了分析,并基于单位化的莫尔-库仑准则,再结合试验数据反算了普通混凝土真实的破裂角范围与最危险破裂角,结果表明:(1)立方体中存在左右对称的崩解区和上下对称的刺入区,前者有脱离立方体向外侧脱落的趋势,刺入区实质上是端头约束影响区,竖直方向有刺入立方体的趋势;(2)单轴压缩时普通混凝土的真实破裂角在64～83°之间,最危险破裂角在73°附近,而立方体中45°以上的破裂面受到边界约束的影响,致使实际破裂面与真实破裂面不重合,导致测得的抗压强度比真实值偏大,引起了形状效应;(3)增加高宽比可以改变边界约束对破裂路径的影响,对于工程上的普通混凝土,三倍高宽比是消除形状效应的临界值.

There is friction between the machine head and the contact surface of the concrete test block in the test of the compressive strength. This force constrains the displacement of the upper and lower end face of the test block. Finally, the boundary conditions of the upper and lower surfaces have an influence on the real strength. In view of this phenomenon, the shear band in the concrete cube subjected to strong constraint was analyzed. Moreover, the actual crack angles range and the most dangerous rupture angles of ordinary concrete were calculated based on the Mohr-Coulomb criterion of unitization and the test datum.The results show that:(1)There are two kinds of zone in the cube, one is the disintegration zone which are left-right symmetric. These zones have a tendency that will detach from the cube. The other one is thrust zone which is top-bottom symmetric. These zones are within the influence of the end restraint, which has a trend of penetration into the cube in the vertical direction.(2)The true rupture angles of ordinary concrete are between 64 °～83° subjected to uniaxial compression, and the most dangerous rupture angles are at about 73°, but the fracture surface whose dip angle is 45 ° and above are affected by the boundary constraint. These cause the actual fracture surface not to coincide with the true rupture surface, so the measured compressive strength is larger than the true value. This phenomenon is shape effect;(3)The boundary constraint has an effect on the rupture path, which can be changed by adding depth-width ratio. To eliminate the shape effects, the critical ratio of height to width should be 3:1 for ordinary concrete used in engineering.

引言
1 单轴压缩时立方体的破坏特征与机理
2 普通混凝土的破裂角范围与最危险破裂角
3 立方体测抗压强度与破裂形态
4 分析与讨论
5 结论

图1 轴向压缩时的应力分量<br/>Fig.1 Stress component of axial compression

图1 轴向压缩时的应力分量
Fig.1 Stress component of axial compression

图2 摩尔-库仑准则的图解法<br/>Fig.2 Graphic method of the Mohr-Coulomb criterion

图2 摩尔-库仑准则的图解法
Fig.2 Graphic method of the Mohr-Coulomb criterion

表1 规范中不同强度等级混凝土的强度参数标准值[17]<br/>Tab.1 Standard values of strength parameters for concrete with different strength grades in the specification

表1 规范中不同强度等级混凝土的强度参数标准值[17]
Tab.1 Standard values of strength parameters for concrete with different strength grades in the specification

表2 不同强度等级混凝土抗剪强度标准值[18]<br/>Tab.2 Standard values of shear strength of concrete with different strength grades

表2 不同强度等级混凝土抗剪强度标准值[18]
Tab.2 Standard values of shear strength of concrete with different strength grades

$表3 取标准值时不同强度等级混凝土破裂面摩擦系数 Tab.3 The fracture surface friction coefficient of concrete with different strength grades$

表3 取标准值时不同强度等级混凝土破裂面摩擦系数
Tab.3 The fracture surface friction coefficient of concrete with different strength grades

$表4 不同强度等级混凝土的破坏角范围和最危险破裂角/(°) Tab.4 Failure angle range and most dangerous fracture angle of concrete with different strength grades/(°)$

表4 不同强度等级混凝土的破坏角范围和最危险破裂角/(°)
Tab.4 Failure angle range and most dangerous fracture angle of concrete with different strength grades/(°)

$图3 不同强度等级混凝土破裂角范围的图解法 Fig.3 Graphic method for fracture angle range of concrete with different strength grades$

图3 不同强度等级混凝土破裂角范围的图解法
Fig.3 Graphic method for fracture angle range of concrete with different strength grades

$图4 立方体测抗压强度时的破裂形态 Fig.4 The fracture morphology of cube in the measurement of compressive strength$

图4 立方体测抗压强度时的破裂形态
Fig.4 The fracture morphology of cube in the measurement of compressive strength

图5 上下端面强约束条件下的剪切滑动面<br/>Fig.5 Shear slip surface of cube subjected to strong constraint from upper and lower surfaces

图5 上下端面强约束条件下的剪切滑动面
Fig.5 Shear slip surface of cube subjected to strong constraint from upper and lower surfaces

图6 上下端面强约束条件下剪切带的叠加<br/>Fig.6 The superposition of shear bands of cube subjected to strong constraint for upper and lower surfaces

图6 上下端面强约束条件下剪切带的叠加
Fig.6 The superposition of shear bands of cube subjected to strong constraint for upper and lower surfaces

图7 上下端面强约束条件下的剪切带分布<br/>Fig.7 Shear band distribution of cube subjected to strong constraint from upper and lower surfaces

图7 上下端面强约束条件下的剪切带分布
Fig.7 Shear band distribution of cube subjected to strong constraint from upper and lower surfaces

$图8 不同高宽比时的最危险破裂角对比 Fig.8 Comparison of the most dangerous fracture angles at different aspect ratios$

图8 不同高宽比时的最危险破裂角对比
Fig.8 Comparison of the most dangerous fracture angles at different aspect ratios

图9 试件中的纯压区[2]<br/>Fig.9 Pure pressure region in prism test specimen

图9 试件中的纯压区[2]
Fig.9 Pure pressure region in prism test specimen

表5 强度折减系数α1的取值[17]<br/>Tab.5 Strength reduction factor α1

表5 强度折减系数α1的取值[17]
Tab.5 Strength reduction factor α1

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备注

引言

1 单轴压缩时立方体的破坏特征与机理

2 普通混凝土的破裂角范围与最危险破裂角

3 立方体测抗压强度与破裂形态

4 分析与讨论

5 结论

期刊信息