Applied Mechanics and Materials Vols. 204-208

Abstract: With the development of wall innovation, the appearance of regeneration concrete hollow block has an important operation significance for building energy saving and high efficiency recycling of waste concrete. The paper introduces a new green wall material—regeneration concrete hollow block and analyzes the feasibility of its application from the point of macroscopic and technical economy. The paper forecasts the direct and indirect economic benefits after its application in order to promote the extension of regeneration concrete hollow block.

Abstract: Building fires can cause severe damages to not only human life but also building structures. Therefore, every nation requires a building regulation related to fire in aspect of safety of human and structural stability. The structural stability under fire condition can be evaluated by the fire test defined in each nation’s standard. However, the results from the test don’t satisfy the real situations of the building such as fire loads, opening size, loading and boundary condition of structural members, and etc. Meanwhile, performance based fire engineering design is regarded as an alternative evaluation method of fire. The fire engineering method has been regarded as a more rational method than the prescriptive method in terms of accuracy and cost efficiency. Recently, the limit temperature method is regarded as the easiest fire engineering method to evaluate the structural stability under fire. To make the backbone of a specification of limiting temperature method, limiting temperatures of various structural members are required. In this paper, in order to make a database of the limiting temperatures of H-section columns and beams, fire test programs with loading were conducted and the limiting temperatures and fire resistance were derived.

Abstract: Finite difference method (FDM) is used to numerical stimulation analysis for chloride diffusion in concrete. By numerical computing, comparison of chloride content profile in different concrete members with different sectional shapes is made. Calculation and comparison show the chloride content prolife in rectangular and circular section has obvious difference. If the side length of rectangular section is equal to the diameter of circular section, as well as the material property and environment, the chloride content in rectangular section is higher than that in that in circular section. In the calculation example, the chloride content at the depth of reinforcement of circular section is about 50-60% that of rectangular section. This tendency is more remarkable in less section dimension, as well as less cover thickness. With the increasing of section, the ratio of difference becomes to be less until to a constant value. In durability design and service life prediction of concrete structures, the section shape and dimension influence should be taken to consideration.

Abstract: BP neural network detecting concrete defect, convergence is slower and accuracy is not high. In order to overcome the defect of BP algorithm, using a combination of Ant Colony optimization algorithm and BP neural network method, a mathematical model of Ant Colony neural network was established, enables Ant Colony neural network training, and verify the validity of the method. And concluded: using ant Colony neural network identification of concrete defects, the identification of the location more effective than on size.

Abstract: In order to enhance the shear capacity of reinforced concrete (RC) beams more efficiently, a thought to strengthen concrete beams by using steel bar/wire mesh mortar was proposed. A comparison experiment study on shear behavior of two kinds of strengthening RC beams(namely steel bar mat(S)mortar strengthening, and steel bar / wire mesh(SW) mortar strengthening) was carried out. The experimental results show that SW strengthening can keep the advantages of a better dispersion of reinforcement due to the addition of wire mesh, leading to a much higher initial diagonal crack load, and a better control to the crack propagation of the strengthened beams. The initial diagonal cracking load and the shear capacity of SW strengthened beams are 83% and more than 30% higher than those of S strengthened beams respectively, while the reinforcement ratio of the formers is only 22% higher than that of the laters. The working mechanism of SM mortar strengthening was discussed.

Abstract: In order to supply basic principles for durability design of concrete structures, the corrosion mechanism of concrete structures under common atmospheric environment was analyzed. The climatic condition of temperature (T) and relative humidity (RH) which has important impacts on concrete carbonation, was chosen as main factors to grade. On the basis of partition for the influence degrees of temperature and relative humidity on the concrete carbonation, the environmental action in concrete structures was classified with a comprehensive evaluation method. The results show that both temperature and relative humidity can be partitioned into five grades. The concrete carbonation is classified into five grades according to influencing factors of temperature and relative humidity to concrete carbonation levels. The carbonation depth which is calculated with the average of positive temperature and relative humidity is taken as the control index of classification.

Abstract: Through accelerated method using external current and 5% Nacl solution, different corrosion results of rebars in columns were attained to study damage patterns of columns under large eccentric loading. Results indicated that columns with different corrosion degree due to different corrosion time developed defferent damage modes. Firstly, results show typically large eccentric damage for columns with different corrosion degree. Secondly, with the increase of corrosion degree, different damage patterns appear under lower loading including reduction of compressive damage scope, expansion of crack zone and earlier crack. These results can be considered as reference to guarantee safety of structures with eccentric loading under corrosion environment.

Abstract: Mechanical behavior and bearing capacity of self stress ceramsite concrete filled steel tubes (noted as SCCST) after exposure to fire are experimentally studied. Effect of the parameters, such as value of furnace temperatures, self stress on the post-fire bearing capacity and ductility of the specimens after exposure to fire were especially discussed. The experimental results show that all the specimens of SCCST have higher post-fire bearing capacity and better ductility, and there was no obvious descending segment in the load-strain curves of the most specimens after exposure to fire. It was concluded that the furnace temperature subjected to the specimens and the initial self stress produced in the specimens of the composite short columns has some effect on the axial bearing capacity of ceramsite concrete-filled steel tubular short columns after exposure to fire, and the volume of expansion agent of 10% has most great effect on post-fire bearing capacity of SCCST after exposure to fire.

Abstract: Based on Ježek method of computing the elastic-plastic buckling of the member under the axial compressive load and the bending moment, considering the initial imperfection, the analytical expressions of calculating the ultimate load of buckling about the neutral axis with the maximum moment of inertia for an H-shaped member are derived. Using the elastic-plastic finite element method and the theory of nonlinear buckling, the impact by initial geometric imperfections on the H-shaped steel member under the axial compressive load and the bending moment are analyzed and the numerical solutions of ultimate bearing capacity are obtained. By compared with the values of the finite element method (FEM), it shows that the analytical method in this paper is valid. The results of the example show that the presence of initial imperfections reduces the ultimate bearing capacity of the steel member to a great extent. It is also found that the influence of the initial geometric imperfection on the ultimate bearing capacity of member is smaller when the bending moment increases.

Abstract: A chemo-damage model for concrete affected by alkali-aggregate reaction (AAR) is presented. Redistributing weights, determined by the applied stresses in the concrete, are introduced to control the anisotropic expansion of the AAR-affected concrete. Accelerated tests are analyzed using the proposed model. The computed strains of the specimens are compared with the experimental measured strains. It demonstrated that the proposed model can consider the effects of applied stresses on AAR-induced expansion with reasonable accuracy.