Advanced Materials Research Vols. 163-167

Abstract: This paper attempts to reveal the aging behaviors of natural rubber (NR) used in isolation bearings. Using various degradation factors like thermal oxidation, ultraviolet, ozone, low temperature ozone, salt water and acid rain, a series of environmental accelerated aging tests were conducted to investigate the aging characteristics. From the test results, it was clarified that the thermal oxidation is the dominant degradation factor, which hardens the rubbers and results in a significant drop of performance. This study is fundamental to predicting the lifecycle of NR isolation bearings.

Abstract: Since the performance functions of large complex structures can not be expressed explicitly in the process of reliability analysis, support vector machines (SVM) with good ability of generalization are used as the response surface function based on the small training samples. The uniform design method was adopted in selecting the training data. The least support vector machines (LS-SVM) were used to find the support vectors. The limit state function was expressed by the LS-SVM regression. Reliability analysis was then performed by the usual reliability method (e.g., the first-order reliability method, the second-order reliability method or Monte Carlo) on the response surface. The results of calculations of numerical examples and a typical cable-stayed bridge show that LS-SVM using the uniform design method can well approximate the real response of complex structures which has a good efficiency and accuracy and can be applied in complex structures.

Abstract: Because of the facts of reinforced concrete structures materials and used environment, very severe durability problems occurred in reinforced concrete structures. Research on reinforced concrete structures durability has become one of the world-wide concern problems in structural engineering. Extension method based on matter-element theory and conjunction function is introduced to evaluate durability of reinforced concrete structures in this paper. The matter-element model for durability evaluation of reinforced concrete structures is established by chose seven evaluation indexes. Applying simple conjunction function to calculate the weight coefficient of evaluation indexes can reduce the error caused by subjective judgment, and makes the results more objective. The research indicates that extension method is reasonable and feasible in evaluating durability of reinforced concrete structures.

Abstract: Introduced after the Wenchuan earthquake, the situation of teaching buildings collapsed, buildings destroyed by the actual picture of the location and characteristics of some typical building damage, building damage arising described several major reasons put forward the views of housing and construction reinforcement, stress the seismic design and the importance of project quality management.

Abstract: Chloride attack has been identified as one of the most important factors initiating the corrosion of reinforcing bars. Chloride penetration into the concrete is generally recognized as a diffusion-controlled process. Material properties of the concrete structures are widely recognized that it is of intrinsic randomness, and it is an urgent task to develop a stochastic analysis method for chloride diffusion. Firstly, a deterministic boundary element method with new time marching scheme is developed and described. The diffusion coefficient is described as the random field and discretized based on the local average theory. In order to conduct a stochastic analysis, combining the Monte-Carlo simulation technique with the proposed BEM, the Monte Carlo stochastic BEM for stochastic analysis is proposed in this paper and used in numerical examples. Stochastic analysises presented in this paper provide basis for the reliability analysis of the durability of the concrete structures.

Abstract: Depending on the actual service condition of sub-health bridge, the following investigation is carried out: 1)The concept of damage limit state is proposed, from which the subject of the serviceability carrying capacity is revealed, then the evaluation path of serviceability carrying capacity of sub-health beam is given.2) The difference between the reliability of sub-health bridge and new bridge is analyzed, consequently, the problem about reasonable limit vehicle load is solved preliminarily in theory.

Abstract: At present, durability of concrete structures has become one of the problems widely concerned by the academic and engineer circles in civil engineering. Shanghai Yangtze River tunnel project is the engineering background of the paper. The sensitivity analysis has been studied on carbonization life's influencing factors of Shanghai Yangtze River Tunnel segment structure with the method of grey -correlation theory and uniform design. The results show that concrete cover depth has the most important effect. The other less important influencing factors in turn are as follows: concrete compressive strength, fly ash substitution amount, temperature, relative humidity and CO2 concentration. The research achievement has been using in the design and construction of Yangtze River Tunnel, and good results have been achieved.

Abstract: For decreasing sodium chloride consumption and pollution, the possibility of decreasing concentration of NaCl in the rapid chloride migration coefficient test (RCM) is studied when decreasing NaCl solution from 10% to 3%, 1% and 0.5% by mass, respectively. The chloride-penetration depth and the migration coefficient and electric charge are studied in this experiment. The results as followings: (1) When NaCl concentration is decreased from 10% to 3% in the RCM test, the error is within 5% between migration coefficient values of concrete. It is suggested that a 3% NaCl solution can be used to replace a 10% NaCl solution in Chinese standard GB/T 50082-2009. (2) The content of NaCl solution has a little effect on the electric charge passed. (3) It is not suitable to use the test results of mortar specimens to count conversely the results of concrete specimens, but can use mortar specimens to estimate the performance of different binders.

Abstract: In this paper, the corrosion of steel during the accelerated corrosion test was investigated through linear polarization method. The critical chloride ion concentration was determined according to the mentioned experimental results. Through the analysis of the experimental results of accelerated penetration test, the service life prediction equation of concrete structures was established. The 20V predicted results exhibited good compliance with the measured values, which indicated the reasonableness of the mentioned prediction method.

Abstract: During the service process of a P.C. bridge, the mechanical properties of materials (including concrete and steel) will deteriorate, and eventually result in the decrease of ultimate bearing capacity. Considering it’s structural behavior, degenerate solid elements were used to set up a three-dimensional model. By taking prestressed reinforcement as a part of structure, the equivalent nodal load was provided to calculate the effect of tensioning bars. The T.L. method was adopted to consider the geometric nonlinear effect. The Ohtani & Chen model was used to simulate the concrete material nonlinear behavior, and for prestressed steel strand and common reinforced, linear hardening and ideal elastoplastic model were adopted respectively. A P.C. continuous rigid frame bridge was employed for the case study, on the basis of material performance deterioration, the ultimate bearing capacity analysis of P.C. bridge structure was carried out. The results show that material deterioration has great impact on ultimate load capacity of structure: the load factor on limit state dropped rapidly from 13.9085 at t=0a to 7.8265 at t=100a, the corresponding safe index decreased from 2.265 to 1.581, and brittle characteristics was aggravated at the same time.