Research On Mechanical Properties Under Cracks Control Of Concrete Perforated Brick Wall

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.