【作者】 李妍；

【导师】 孟广伟；

【作者基本信息】 吉林大学 ， 固体力学， 2011， 博士

【摘要】 随着我国墙体材料改革和节能措施的贯彻执行,各种新型墙体材料的出现极大地促进了现代建筑结构的发展,其中的混凝土(砼)多孔砖材料已成为我国大力发展替代粘土制品的主导产品之一。但是,阻碍混凝土多孔砖发展的最突出问题就是墙体的裂缝。裂缝是固体材料中的某种不连续现象。大量的工程事故告诉我们,土木工程建筑结构的破坏和倒塌往往都是从裂缝的扩展开始的,而且建筑高能耗的原因也常常是由于某些裂缝的存在。可见,研究墙体裂缝控制相关的材料力学性能在土木工程领域具有重要的现实意义。几乎所有的墙体在加载以前都存在微裂缝。裂缝的存在不仅仅降低了墙体的质量,如整体性,耐久性和抗震性能,还给居住者在感观上和心理上造成不良影响。而且,通过对比新颁布的砌体结构设计规范(GB50003—2001)与原规范,我们发现,新规范不仅在裂缝控制措施上增加了许多具体内容,而且对裂缝的控制更加严格,这充分说明墙体裂缝问题已引起国家相关主管部门的高度重视。因此,正确分析墙体裂缝的产生机理,明确裂缝开裂的临界状态,不同裂缝成因下墙体的受力状态,加强混凝土制品墙体的抗裂措施,已成为国家行政主管部门、本领域专家学者、以及房屋开发商、建筑商共同关注的课题。本论文正是在此背景下,在建立混凝土多孔砖墙体的本构关系、确定混凝土多孔砖墙体的弹性模量基础上,将复合材料力学和线弹性断裂力学的基本理论应用于墙体的裂缝控制研究中,运用复合材料力学的修正剪滞理论,结合能量法则推导出了混凝土多孔砖墙体的等效断裂参数的计算模型,建立了墙体开裂的断裂判据。并对墙体的变形裂缝—干燥收缩裂缝进行了可靠度计算,同时进行了相关的力学性能试验。本文的主要成果有:1、系统的介绍了砌体结构的本构关系,建立了混凝土多孔砖墙体的本构关系。对混凝土多孔砖墙体进行了应力—应变全曲线的测定试验,通过实验数据的线性回归,利用最小二乘拟合法,得到了两种不同形式的混凝土多孔砖墙体本构关系数学表达式。2、确定了混凝土多孔砖墙体的弹性模量。自行设计了更加符合混凝土多孔砖真实受力性能的墙体及墙体材料(混凝土多孔砖、砂浆)的弹性模量的试验测定方法。并从试验统计资料、混凝土多孔砖墙体受压本构关系及由多孔砖、砂浆的弹性模量等三个方面得到了墙体的弹性模量。可以看出,从试验统计资料得到的计算结果与试验结果、现行规范的取值更加吻合;而由多孔砖、砂浆的弹性模量得到的结果有利于利用混凝土多孔砖墙体材料的力学性质深入研究墙体的受力性能及开裂、破坏机理。3、从断裂力学的角度出发,提出了混凝土多孔砖墙体的等效断裂参数的实用解析模型。根据线弹性断裂力学和复合材料力学的基本原理,运用修正的剪滞理论,分区引入变异层,建立了分层剪滞模型;由能量法则推导出了求解无筋墙体等效断裂参数的解析计算模式;通过相关试验获得的数据,利用有限元分析方法,得到了对应数值解的解析解,且与相关试验对应的数值解相比,解析解的均方差和变异系数更小,由此可以看出,本文的解析方法具有很好的鲁棒性。结果还证明了无筋墙体等效断裂参数是与试件尺寸无关的断裂参数。4、建立了混凝土多孔砖墙体干燥收缩性能的计算模型。对特定条件下混凝土多孔砖墙体进行了连续60天(d)的干燥收缩变形试验,分析了砌筑砂浆、龄期、混凝土多孔砖初始含水率、相对湿度和温度对混凝土多孔砖墙收缩的影响,并提出了标准养护条件下及非标准养护条件下混凝土多孔砖墙收缩率的估算公式,同时进行了足尺寸墙片的干缩试验,并在此基础上提出了墙体的防裂措施,研究结果可为混凝土多孔砖在我国北方工程中的应用提供参考依据。5、在试验的基础上,提出了一种基于干燥收缩变形抗裂性能的可靠度计算方法。结合相关试验结果,给出了较为合理的收缩应力与变形的取值方法,得到了位移和应力的变化规律,从定量角度考虑了其抗裂效果,明确了干燥收缩值及其影响因素的概率特性,建立了砼多孔砖墙体在干燥收缩作用下的正常使用极限状态方程,从强度条件和线弹性断裂力学的断裂判据两个角度对墙体的变形裂缝进行了可靠度评估,给相关结构设计规范提供了一个有益补充。更多还原

【Abstract】 With the reform of wall materials and energy-saving measures being carried out, the emergence of a variety of new wall materials, greatly promoted the development of modern architecture, one of the leading products of the concrete perforated brick materials have become a substitute of clay products. However, the cracks of wall is the most serious problem that hindered the development of concrete perforated brick wall. The crack is a certain discontinuous phenomenon in solid material. A lot of engineering accidents have told us, civil engineering structures are often damaged and collapsed from the beginning of crack extension, and the reason of its high energy consumption is due to the existence of some cracks. It can clearly be seen that researching on mechanical properties under cracks control of the wall in the field of civil engineering has important practical significance.Most of the wall has the micro-cracks there before loading. The existence of cracks not only reduce the quality of the wall, such as integrity, durability and seismic performance, but also gave residents adverse effects in the sensory and psychological. Moreover, by comparing the new promulgated design of masonry structures(GB50003-2001) with the original specification,, we found that the new specification is not only add a number of specific content in crack control measures, and more stringent on the crack controls, which fully shows that the problem of the wall cracks has caused the relevant state authorities attach great importance to. Therefore, to analyse the mechanism of wall cracks correctly, know the critical state of cracking clearly, the wall’s stress state under different cracks, strengthen the wall of the cracking of concrete measures for products, all this has become topic which the national administrative departments, experts and scholars in this field and housing developers, builders pay attention to.This paper is in this context, the first attempt to apply the basic theory of linear elastic fracture mechanics to the study of the wall cracks, and uses the modified shear lag theory of composite mechanics, considering the constitutive relationship wall, material parameters and other factors, using the finite element method, combined with the law of energy derived concrete perforated brick wall of the equivalent fracture parameter calculation model, founding the wall cracking fracture criterion. The first attempt to analyze the reliability of the deformation of the wall cracks - drying shrinkage cracks, and also carried out the experiments of the related mechanical properties. This paper’s main results are as follows:1. It has more detailed the constitutive relationship for masonry structures, noting that the various expressions and characteristics of the constitutive curve ; On the basis, concrete perforated brick wall has been test the stress - strain curve, linear regression through the experimental data using least squares fitting, obtaining two different constitutive form of mathematical expressions concrete perforated brick wall.2. Designed the elastic modulus of the test method which are a more consistent real mechanical properties of concrete perforated brick wall and wall materials (concrete perforated bricks, mortar). The elastic modulus of the wall was received from three aspects of statistics through the test, and the pressure constitutive relationship of concrete perforated brick, elastic modulus of concrete perforated bricks and mortar. It can be seen, the value that statistics obtained from the test results is more consistent with existing codes; the results obtained by the elastic modulus of brick and mortar conducive to the use of the mechanical properties of concrete brick wall depth study of the materials mechanical properties and cracking, failure mechanism of the wall.3. According to the basic principles in the composite material mechanics and the linear elastic fracture mechanics, based on the modified shear lag theory and by introducing the variable layer in different zones, the layered shear lag model is built. Then based on the energy law, an analytical form which is to solve the equivalent fracture parameter of wall is derived. Finally, against the solutions of the related experiments, the analytical solutions of the equivalent fracture parameter of wall are obtained. The results show that in the case of varying sub-layers, the equivalent fracture parameter of wall is a size-independent fracture parameter.4. Based on the results for the dry shrinkage deformation of concrete perforated brick wall cured in the given several kinds of conditions within 60 days, the main factors affecting the dry shrinkage deformation such as bricklaying motor, the curing ages, the initialization moisture content, the relative humidity and the ambient temperature. The formulas in the standard environment and the natural environment which estimated the dry shrinkage deformation of concrete perforated brick masonries are suggested, and this may be as a reference for the application of concrete perforated bricks in north engineering.5. Based on the experiment, the reliability of shrinkage deformation method has been proposed.Combined with the experiment results, the method with dry shrinkage stress and deformation was put forward, the variety disciplinarian with displacement and stress was known, quantitative research has done to see the effects of cracking, the propability characteristic of dry shrinkage value and effects were analyzed. So a serviceability limit states equation of concrete perforated brick wall in the drying shrinkage was established, from two different point of view to evaluate the deformation of the wall cracks including strength conditions and linear elastic fracture mechanics of fracture criterion, the first attempt to use the basic theory of fracture mechanics to analyze the reliability of the wall cracking, which related to structural design for is a useful addition. It provides a useful complement to the relevant structural design codes.更多还原