Advanced Materials Research Vols. 163-167

Abstract: Wind erosion is one of the most familiar and serious diseases to Ancient Earthen Architectures (AEA). As far as the durability of AEA is concerned, most previous researches focus on laboratory test with little on field simulative test. In order to find out actual effect of PS (high mole ratio potassium silicate) in enhancing the durability of AEA under wind erosion, this paper combines laboratory test and field test. In the former part, we treated samples with PS of 7% and 10%, then carried out laboratory tests on water stability and compressive strength, as well as wind tunnel tests on wind erosion durability. In the latter part, we infiltrated the test region with PS of 3%、5% and 7%, and carried out wind erosion test on field. The results indicate that the compressive strength and water stability of PS-treated samples are obviously advanced. In the wind tunnel test, the critical wind speed of untreated and treated samples respectively are 12m/s and 20 m/s. In the field test, the durable time of being eroded increases and the failure depth of test region decreases along with the increase of PS concentration. The surface layer of W starts exfoliating in short time, the eroding styles of W3 and W5 are delves-little piece-large piece and delves-little piece, however, there are only several delves in the W7. Laboratory and field results indicate that the PS can to a large extent change the characters of soil, and the durability of AEA under wind erosion is enhanced along with the increase of PS concentration.

Abstract: To reasonablely assess the residual fatigue life of aged existing reinforced concrete(RC) bridges, axial tensile fatigue tests were conducted on fifteen naturally carbonation-induced corrosion steel bars. The fatigue test results indicate that the existence of corrosion pits reduces the fatigue life of steel bars significantly under the same fagitue stress; with the development of corrosion, the fatigue life of steel bars decays according to negative power exponent law approximately and the attenuation rate increases with stress level augment. The fatigue deterioration law of natural corrosion steel bars is similar to that of accelerated corrosion steel bars, but the attenuation rate is different from that of accelerated corrosion steel bars, and also the influence of stress level on the attenuation rate is just cross to that of accelerated corrosion steel bars. For the complexity of fatigue and corrosion, further pertinent conclusions remain to be confirmed.

Abstract: As geosynthetics is made from polymer, its durability is one of the most important issues people have been concerning. Based on the analysis of data gotten from laboratory, field tests and engineering samplings, the reasons for geosynthetics durability damage are summarized, the injury rules and main factors in various applications are analyzed; after studied the existing durability prediction methods, Support Vector Machine (SVM) theory is applied to predict the durability, and an example is analyzed in which temperature, humidity, UV radiation intensity and the aging time were set as input parameters, residual tensile strength and elongation rate were set as output parameters.

Abstract: In order to solve the problem of concrete cracking in wellhead groove with large longitudinal length, shrinkage tests of concrete containing fly ash and slag in natural environment were conducted. According to the experimental study, the shrinkage model of concrete based on BP neural network is established and the results from model agree well with the measured results. Then the effect analysis of single factor on shrinkage using the neural network model is carried out. Simultaneously, the optimal mix proportion of concrete is successfully predicted by orthogonal experiment of numerical simulation method, so that it provides reference to the control of concrete shrinkage for the engineering structure.

Abstract: Scientific prediction the residual life of existing reinforced concrete elements is an important basis for assessment the structures. The resistance probabilistic density function of reinforced concrete elements was proposed by analyzing the random processes of resistance attenuation of concrete and steel bars. Since the factors of concrete durability damaged and materials deterioration , considered practical conditions of service structures and durability failure criteria of concrete members, a method of calculation the residual life was given, which is verified reasonable through the engineering case.

Abstract: The safety and serviceability of RC structures are time-dependent due to degradation phenomena, therefore assessing the fulfillment of required levels of safety and serviceability up to the end of the design working life of the structure is particular important. Among the most frequent environmental attacks affecting RC structures, reinforcement corrosion is considered the most dangerous source of degradation, which may occur only after depassivation due to carbonation of concrete cover, penetration of chloride ions, or a combination of both. In this paper, the effects of rebars corrosion on seismic response of RC structures were presented. A case study was analysed using time history analyses, in sound as well as damaged conditions, assuming a moderate corrosive attack. The outcomes were discussed in terms of displacement time history curves and acceleration time history curves. In addition, the interstory drift obtained form time history analyses was compared and discussed with the limit value provided by Code for seismic design of building.

Abstract: Many uncertain factors, e.g. surrounding rock physical and mechanical characteristics, are important influence effecting on lining structure safety. By comprehensively considering uncertainties of surrounding rock conditions (lining structure and initial stress), we put forward a new method used to quantitative analysis on the lining structure safety. Analyzing the uncertainties and their distribution characteristics of hydraulic tunnels, we adopted stochastic finite elements method to calculate failure probability of lining structures corresponding to various geological conditions, and then the reliability and sensitivity were achieved. Applying the presented method to a practical project, we got the failure probability of the tunnel lining structure under the construction condition, which provided great support for structure optimal design and tunnel construction safety protection.

Abstract: The reliability of existing double-curvature bridge strengthened with augment section method is put forward based on time-dependent reliability theory. The concerned statistical parameter is taken by using the finite element software. First-order second-moment method is used to evaluate the reliability indexes which estimate the working state of the structure. Combined with a practical example, the time-dependent reliability is illustrated.

Abstract: Tunnel and underground engineering projects have certain failure risks during construction and operation, including the risk of durability failure to which the study is not enough. In this paper, a whole set of research method for analysis, assessment and calculation on durability risk was proposed on the basis of identification to durability risk factors of large underground concrete structures. That is: this paper provided a method of reliability calculation by establishing failure mode and limit-state-equations according to reliability theory; then, classified and collated various risk factors by taking methods of analytic hierarchy process (AHP) and fault tree analysis (FTA); after that, the quantitative analysis of structural durability was done in accordance with Monte - Carlo (M-C) method. Finally, as an example, for the project of passage across the Yangtze River in Chongming, Shanghai, the above methods were applied to estimate the risk of durability failure of segment component. Effective measures and methods were presented and adopted to enhance the durability capacity of structure according to the results of analysis and assessment.

Abstract: The key issues in the theory of interval number fuzzy comprehensive evaluation are discussed in this paper, which includes weight interval calculation, quantitative index dimensionless method and etc. Due to the deficiency of “line method” for interval number formation, one improved method is given to increase the stability of interval number. Then the existing problems of several initial evaluation models are discussed, and the probability theory is introduced to improve evaluation model combined with coefficient of variable weight method. This improved interval number fuzzy evaluation method is adopted on one concrete cable-stayed bridge to general evaluate its safety and durability. The result shows that this improved fuzzy evaluation method can well reflect the general working status of the bridge and have good feasibility and practicality.