单轴和三轴应力下棱柱体混凝土力学特性

发布时间：2018-03-22 06:14

本文选题：棱柱体混凝土　切入点：单轴压缩　出处：《北京交通大学》2017年硕士论文　论文类型：学位论文

【摘要】：不同材料、不同形状尺寸的混凝土在不同的受力状态下会表现出不同的变形破坏特征,破坏强度也会有不同的变化,而目前关于受力更符合实际情况的棱柱体的三轴试验极少。本文研究了使用棱柱体试块(方形截面)在液压三轴室内开展常规三轴压缩试验的方式和技术,利用常规三轴设备开展棱柱体混凝土在不同侧压下的三轴压缩试验以及不同长宽比试块的单轴压缩试验。根据得到的单轴压与三轴压试验结果,分析了棱柱体混凝土强度特征、变形特性及试件的破坏形态,拟合了棱柱体混凝土三轴压下应力-应变全曲线,最后将同一试验机上开展的不同长宽比棱柱体混凝土单轴试验进行总结和分析,形成系统的力学性能的研究,具体研究内容如下:(1)研究了使用常规三轴设备对(正方形截面的)棱柱体试块进行三轴试验的关键技术和方法,经过试验检验,该方法方便可行。1)自制了与试块形状配套的横向位移传感器,在有限的压力室空间便于使用,且经验证量测设备满足精度要求。2)设计加工了与棱柱体试块和三轴设备匹配的上下压头和适用于不同尺寸试块的底座压头。3)对三轴设备的测量系统进行改造,通过加装一套更为先进的采集系统,使外置系统与三轴设备的内置测控系统能够联合使用,解决了三轴系统中的通道数量不足、采样速率偏低、电位器数值波动等问题。(2)开展了棱柱体混凝土常规三轴试验,分析混凝土在三轴应力下的强度及变形性能。1)分析了棱柱体混凝土单压和三轴压试验试件的破坏形态,结果表明围压和减摩对其有显著影响。2)对三轴定侧压试验数据进行处理,分析棱柱体混凝土三轴抗压强度及相应变形、围压之间的关系。3)三轴试验选用减摩与不减摩两种情况进行应力-应变曲线和特征值等的对比,发现随着围压的增大,端部效应对棱柱体混凝土的三轴强度影响逐渐减小,在围压为30MPa时,减摩与不减摩试块的应力-应变曲线最为接近。4)对轴向应力-应变曲线拟合,并分别用D-P准则、Rechart破坏准则和Ansari常用的三种破坏准则来描述棱柱体混凝土的强度,结果显示Ansari破坏准则及D-P修正准则与实际破坏强度拟合程度较好。(3)采用4种尺寸的棱柱体试块(分别为70.7mm×70.7mm×175mm、70.7mm×70.7mm×105mm、70.7mm×70.7mm×70.7mm 和 70.7mm×70.7mm×40mm)研究棱柱体混凝土的单轴力学性能。1)通过单轴试验分析棱柱体混凝土的尺寸效应,结果显示立方体随着几何尺寸的增加,混凝土试件的单轴受压峰值应力和峰值点应变均降低,当几何尺寸减小时,试件的峰值应力降低而峰值点应变增大,显示出尺寸效应现象。
[Abstract]:Concrete with different materials and shapes and sizes will exhibit different deformation and failure characteristics under different loading conditions, and the failure strength will also vary. However, there are very few triaxial tests on prisms which are more in line with the actual conditions. In this paper, the methods and techniques of using prism test blocks (square sections) to carry out conventional triaxial compression tests in hydraulic triaxial chamber are studied. The uniaxial compression test of prismatic concrete under different lateral compression and the uniaxial compression test of different ratio of length to width are carried out by using conventional triaxial equipment. Based on the results of uniaxial and triaxial compression tests, the strength characteristics of prismatic concrete are analyzed. The deformation characteristics and the failure pattern of the specimen are fitted to the stress-strain curve of prismatic concrete under triaxial compression. Finally, the uniaxial tests of prismatic concrete with different aspect ratios are summarized and analyzed on the same testing machine. The study on the mechanical properties of the forming system is as follows: 1) the key techniques and methods of using conventional triaxial equipment to conduct triaxial tests on prisms (with square sections) have been studied and tested. This method is convenient and feasible. 1) A transversal displacement sensor matched with the shape of the specimen is made, which is easy to use in the limited pressure chamber space. The measuring equipment has been verified to meet the precision requirement. (2) the measuring system of the triaxial equipment has been modified by the design and machining of the upper and lower pressure head matching with the prism test block and the triaxial equipment and the pedestal head. 3) suitable for different size test blocks. By installing a more advanced collection system, the external system and the built-in measurement and control system of the three-axis equipment can be jointly used, which solves the shortage of channels in the three-axis system and the low sampling rate. The conventional triaxial test of prism concrete is carried out, and the strength and deformation performance of concrete under triaxial stress are analyzed. 1) the failure modes of concrete specimen under uniaxial and triaxial compression are analyzed. The results show that confining pressure and reducing friction have significant influence on the triaxial constant lateral compression test data, and the triaxial compressive strength and corresponding deformation of prism concrete are analyzed. The relationship between confining pressure. 3) triaxial test is used to compare the stress-strain curves and eigenvalues between friction-reducing and non-friction-reducing conditions. It is found that with the increase of confining pressure, the effect of end effect on triaxial strength of prismatic concrete decreases gradually. When the confining pressure is 30MPa, the stress-strain curve of friction-reducing and non-friction-reducing specimen is the closest. 4) fitting the axial stress-strain curve. The strength of prismatic concrete is described by D-P criterion and three failure criteria commonly used by Ansari. The results show that Ansari failure criterion and D-P correction criterion fit well with the actual failure strength.) the uniaxial mechanical properties of prismatic concrete are studied by uniaxial test with four kinds of prisms (70.7mm 脳 70.7mm 脳 175mm, 70.7mm 脳 70.7mm 脳 105mm, 70.7mm 脳 70.7mm 脳 70.7mm and 70.7mm 脳 70.7mm 脳 40mm). The size effect of prismatic concrete is analyzed. The results show that the peak stress and peak strain of concrete specimen under uniaxial compression decrease with the increase of geometric size. When the geometric dimension decreases, the peak stress decreases and the peak strain increases. The size effect is shown.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

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