Advanced Materials Research Vols. 243-249

Abstract: This paper investigates the influences of dosage of ground granulated blast furnace slag (GGBS) (0%, 20%, 40%, 60% and 80%) to chloride diffusion coefficient. And the time dependency of apparent diffusion coefficient as the submerging time from 60 days to 360days has also been studied. The result shows that the addition of GGBS into concrete has great influence on the chloride diffusion. The diffusion coefficients of the mixes containing GGBS decrease rapidly with time than that of the mix PC Control. But there were little differences of the values of apparent diffusion coefficients among the mixes SL20, SL40 and SL60. The addition of GGBS in concrete has great influence on the time dependency of concrete. And the concrete which has 40%-60% replacement of GGBS has greater ability to resist the diffusion of chloride than other replacement.

Abstract: In the analysis on whole structural life-cycle, there are two important factors to need to be considered. One is the determination of design service life of structure, and another is design of structure based on service life. After analyzing deeply the influence factors of life-time index, it can be found that the design service life of structure not only depends on technology level, functional requirement and economic cost factors of structures, but also relate with the specific environmental conditions, using conditions and maintenance conditions of structures. So that, an analysis method of determined design service life of structure is given in this paper. For design of structure on service life, from the view of whole structural life-cycle, a probability reliability-based analysis method of structural service life design and re-design is proposed in this paper. By updating constantly design parameters, the correctness of predicted service life is improved gradually.

Abstract: In a reliability-based design optimization (RBDO) problem, most of the computations are used for probabilistic constraints assessment, i.e., reliability analysis. Therefore, the effectiveness, especially the correctness of the reliability analysis is very important. If the probabilistic constraint is misjudged, the optimization iteration would have convergence problems or arrive at erratic solutions. The probabilistic constraint assessment can be carried out using either the conventional reliability index approach (RIA) or the performance measure approach (PMA). In this paper, the mathematical models to calculate the reliability index in RIA and to calculate the probabilistic performance measure (PPM) in PMA are discussed. In RIA, through estimating whether the mean-value point in safe domain or not, we should use a positive or negative reliability index respectively. In PMA, one should always minimize the performance measure to compute PPM whether the performance measure at the mean-value point is positive or negative, which puts right the wrong mathematical model in some literatures and makes it possible to produce effective and efficient approach for RBDO.

Abstract: In this paper wetting-drying cycle in the natural situation and increasing the concentration of sulfate solution is used in the laboratory , in order to accelerate the sulfate corrosion of concrete. The ultrasonic speed of sound on the opposite face is tested by ultrasonic technique regularly in order to reflect the change of concretes strength with the relative dynamic modulus.And at the same time the cube compressive strength test is used to detemine the corrosioned concretes intensity.Though the trend of relative dynamic modulus development which are in four different conditions to explain that the presence of chlorine ions affected the sulfate corrosion on concretes.Although in the compound solution, the corrosion degree should be depended on the concentration of sulfate ions and chloride ions in compound solution.

Abstract: Based on cyclic loading experiment of nine beams in the two groups, the relationship among the average web stress, initial diagonal crack width and shear capacity of RC beams was studied. Experimental result shows that the decline of the shear strength of the RC beams due to cyclic loading can be characterized by the width of diagonal crack. Under the same load amplitude, the larger crack width is, the greater the decline of the bearing capacity is. Besides, under the same number of cycles, the greater the load amplitude is, the larger the crack width is, the greater the decline in the bearing capacity of beams is. In addition, according to the experimental phenomena and the shear compression failure mechanism of beam, a formula for shear capacity after cyclic loading is derived for engineering use.

Abstract: Randomicity of basic variable results in the problem of structural reliability. A series of statistical parameters is applied in reliability calculation. Statistical parameters are attained by the statistics and analysis of source data of basic variable. However the basic variable source data is imperfect for a lot of structure. On the other hand, the relation of reliability index and basic variable is an important issue in reliability calculation. The two matters are solved in this paper by fuzzy mathematics. First, the matter of statistic data scarcity of load and resistibility and offered scientific evidence for estimation of distributing type of load and resistibility it solved by grey forecast; Second , the correlate degree of reliability index and load is calculated by correlate degree theory which can provide scientific evidence for security inspect of project.

Abstract: Based on the sample range theory in Mathematical Statistics, the general standard variance of vertical capacity of single piles is evaluated according to the data from static load tests, and a method is presented to evaluate the reliability of vertical bearing capacity of pile, of which distribution obeys normal distribution. Finally, results from the case study indicate that it is effective to evaluate the reliability using the method presented in this paper, and the number of tested piles specified in Technical Code for Testing of Building Foundation piles and determining sample range can be interpreted reasonably in theory. Meanwhile, it can give good references to designers to determine the design parameters according to testing piles.

Abstract: By introducing generalized random space conception to deal with the relativity of shear strength variables of rock or soil, the calculation formulas of foundation bearing capacity reliability analysis in generalized random space were deduced and the program was worked out. The reliability of one project’s foundation bearing capacity was analyzed. The results proved that the relativity of random variables affects the reliability analysis result and must be considered.

Abstract: The effects of water-cement ratio on the tensile creep of early-age concrete under constant load were investigated. Creep and shrinkage of concrete under sealed curing condition was researched to determine the tensile basic creep of concrete. The results indicate that, as in compression, creep of concrete in tensile is very sensitive to water to cement ratio. The results also indicate that the tensile creep increases with the water to cement ratio. And that the tensile creep develops rapidly within the first day after loading.

Abstract: As the deterioration of environment, the effect of acid rain on concrete structures is even more serious. The durability problems caused by acid rain are increasingly concerned by the worldwide. In this paper, the method to simulating acid rain solution in laboratory is proposed and the cyclic soaking-drying to accelerate the acid rain attack is introduced on the basis of the survey and analysis on the components of acid rain around China. Considering that the majority of concrete structures are actually under loads, the load devices for durability test are analyzed, and the devices suitable for the multi-factor durability tests are adopted. The above works will be helpful to carry out the neutralization tests and establish the predicting model of neutralization depth for fly ash concrete.