Applied Mechanics and Materials Vols. 578-579

Abstract: On the basis of concrete durability experimental results under the actions of multiple salts and dry-wet cycles, the internal microstructures of concrete subjected to the corrosion damage are studied in this article. The EDX energy spectrum analysis and chemical composition determination are discussed, and the concrete corrosion mechanisms under the actions of multiple salts and dry-wet cycles are studied further. The results indicate that the internal microstructures of ordinary concrete and fly ash concrete in the multi-salt solution are loose and porous after dry-wet cycles. There are a lot of crystals gathering in the concrete cracks. Through the EDX energy spectrum and chemical composition analysis, the main composition in them is CaCO₃, doping with a small amount of Na₂SO₄, Na₂CO₃, or NaHCO₃, etc. While the internal structure of air-entraining concrete is not only relatively dense, but also corroded by multiple salts. Under the condition of dry-wet cycles, the concrete damage by salt corrosion is a complicated process which including both chemical attack and physical function, and the damage speed and degree to crystallization corrosion by salts is quicker and even more serious than that of the chemical erosion.

Abstract: Based on the results of integral structure analysis, a practical program for the reliability analysis of the members is introduced for engineering application. The .NET framework and SAP2000 API were combined to develop this program. The probability distribution parameters of the load and the material are the input parameters and then based on the integral structure analysis results, by combining the Monte Carlo simulation methods and the JC methods, the probability distribution of the load effects and the resistance of the members can be calculated, thus the reliability indices of each member could be obtained. Furthermore, an example was introduced and the comparative study between this proposed method and the conventional method for evaluation of a structure was carried out. The results show that it is a feasible method to evaluate the bearing capacity of a structure by exploiting reliability indices directly and this method can offer more quantitative reliability indicators of the structures.

Abstract: Based on Monte Carlo method, the concrete durability reliability indexes for typical concrete members in 50-year-period of service were calculated under normally moist environment conditions. By taking the typical concrete members under normally moist environment conditions as example, the fuzzy reliability indexes based on durability for crack control criteria provided in GB 50010-2010 were calculated. The calculation results show that the durability reliability indexes are mainly lower than crack control reliability indexes for normally moist environment conditions. To realize the goal that the durability design safety level can be generally closest to crack control safety level, one revision advice was presented for present concrete design code GB 50010-2010 to properly lower the crack control safety level in normally moist environment conditions: the present short period crack width enlargement coefficient should be multiplied with 0.85 so that the calculation guarantee rate will be lowered to 85% for flexural members.

Abstract: According to Lagrange equation in dynamics the motion equation of the mega frame with rubber bearing isolation was established. Its solution was approched with MTALAB language programming. The calculation results show that the seismic isolation system can significantly reduce the seismic dynamic response of inter-story drift. When the first layer support and the second support stiffness coefficient of rubber bearing being 190000 kN/m, and the equivalent damping coefficient being about 20000kN.s/m, the isolation efficiency can reach as high as 50%~88%, which is the best combination.

Abstract: Different from ordinary Portland cement concrete, the Polypropylene Fiber (PPF) concrete is a new type of concrete and is made through mixing PPF into common concrete. To popularize and apply PPF concrete, this paper carried out a series of experimental study on the durability of PPF concrete under chloride environments. In the present study, three chloride environment tests were conducted on PPF concrete with various volume fraction of PPF (0,0.1%,0.3%,0.5%). The scaling of concrete, the chloride penetration in concrete and the microstructure in concrete were determined. The results indicated that the scaled mass and relative dynamic modulus of elasticity loss decrease with the volume of fiber increasing, Cl^- concentration has a much higher content near the sample surface, adding 0.1% PPF into concrete has the perfect resistance of Cl^- penetration. More fibers can delay the development of cracks, but that will reduce the inner density of concrete.

Abstract: Orthogonal experiment is used to study the influence of splitting load and mixing of polypropylene fiber of different volume fraction, different length and different mass ratio of long and short fiber on permeability of chloride ion in concrete. The results show that the chloride ion diffusion coefficient increases as the stress ratio increasing, and the relationship between them approximately agrees with exponential function. The influences of fiber volume fraction and fiber length on permeability of chloride ion in concrete are significant, and using shorter polypropylene fiber in the range of low volume fraction can lower permeability of chloride ion in concrete, whereas long fiber and large volume fraction will increase the permeability. The effect of lowering permeability of chloride ion in concrete is most obvious, when the fiber volume fraction is 0.1%, the fiber length is the combination of 6mm and 9mm, and the mass ratio of long and short fiber is 1:2.

Abstract: China’s current load-carrying capacity evaluation code for highway bridges is a semi reliability-based code. The reliability level of the code is analyzed through a comparative study, and methods used to update the reliability level of this code are specified in this paper. A formula to calculate the implied reliability index is proposed and verified by comparison with calibrated reliability indexes in design codes. Then the formula is used to calculate the implied reliability index with statistical parameters derived from the load and resistance coefficients in the current code. It is proposed that the implied reliability index should be adjusted by considering historical failure rates. Different criteria used to define historical failure rates of highway bridges are discussed. In addition, the paper compares the reliability level, applicability, evaluation frequency, target reliability indexes, and resistance and load coefficients between AASHTO and China’s current code. The paper would serve as a reference for the upcoming research on the updating of current highway bridge Load-carrying capacity evaluation code.

Abstract: Stud shear connector corrosion is an important factor for the durability degradation of steel-concrete composite structures. Stud shear connector corrosion in the natural environment is a slow process, so the shear capacity of deteriorated stud shear connector was studied by accelerate d deterioration using a galvanstatic method in this paper. Then, bending tests were conducted to study the structural behavior of steel-concrete composite beam after stud shear connector corrosion. Experimental results show that with the increase of conduction time, the corrosion rate of stud increases, the shear capacity of stud as well as the flexural capacity of steel-concrete composite beam decreases and the relative bond-slip between steel beam and concrete increases when loading. By the regression analysis of experimental results, formula was proposed to predict the shear capacity of studs after corrosion and the flexural capacity of deteriorated steel-concrete composite beam.

Abstract: In this study, a modified pore structure of cement based material with respect to a path for ingressive ions was established. Of pores in a concrete, gel pores and other entrapped air voids were excluded from modelling the pore structure as no interests are given due to the ions immobilization of cement paste media. To setup the pore structure, the linear traverse method (LTM) was used to distribute air voids along the traverse line in a hexahedron cement paste structure, followed by including entrained air voids to fill up the least space of the cement matrix and making a network of the air voids through capillary pores at the variation in the diameters. Then the mercury intrusion porosimetry (MIP) was used to iteratively approach an accordance rate with calculated one from the above way to get into appropriate convergence value. As a result, for the OPC specimen the developed model shows a somewhat relevant value of 42.4 % of the accordance rate compared to empirical one and 64.24 of the ratio of ionic path to original distance within a concrete.

Abstract: In the present paper, a non-probabilistic reliability method is proposed for slope stability analysis. Soil properties involved in non-probabilistic reliability analysis are viewed as random variables and represented by interval variables. The performance function for slope stability analysis is expressed as the difference between anti-sliding moment and driving moment. The non-probabilistic reliability index is defined as the ratio of the mean value of performance function to deviate. Three examples have illustrated the simplicity and applicability of the method. This method provides a new means for slope stability analysis.