Applied Mechanics and Materials Vols. 351-352

Abstract: Sufficient information about uncertain parameters is unavailable and very costly in the conventional reliability analysis of the retrofitted RC bridge. The non-probabilistic convex set only requires small samples to obtain the variation bounds of uncertain parameters. An interval set denotes the variation range of an uncertain parameter, and two convex sets reflect the relationships of uncertainty parameters. The non-probabilistic reliability analysis model is developed based on limit-state function and convex model. The non-probabilistic reliability index is solved by the gradient projection method. The engineering example shows that the non-probabilistic reliability is reasonable and economical, and perfects the method and theory of reliability analysis for the retrofitted BC bridge.

Abstract: Erosion-resisting characteristics of C25C35 and C50 concrete are tested in an environment of freezing and thawing cycle. The result shows that the corrosion becomes more and more serious under clear water, the liquor of sodium sulfate, the liquor of sodium sulfate and sodium chloride after 300 freeze-thaw cycles. This kind of phenomenon also happens when the water cement ratio becomes increasingly bigger. The concrete samples which are protected by SPUA (Spray Polyurea Elastomer) are in good condition. The main problem is spalling from surface to interior, which shows different tendency in different salting liquid.

Abstract: An inverse first order reliability method (FORM) is presented to solve the safety factors for the in-plane creep stability of concrete filled steel tubular (CFST) arches. In the inverse analysis, the safety factors with or without considering the time-dependent behavior of concrete are introduced into limit state equations for the in-plane stability design of CFST arches. For different target reliability indices and steel ratios, the time-independent and time-dependent safety factors are solved. The results show that the inverse FORM is of good efficiency and applicability. The target reliability indices have little effect on the safety factors for the creep stability of CFST arches. The effects of steel ratios are significant which should be considered in design. For the commonly used steel ratios of CFST arches, the in-plane safety factors for creep stability range from 1.17 to 1.43.

Abstract: Water content is one of key effect factors on the dynamic elastic modulus, which is an important damage assessment index of concrete structures induced by freeze-thaw cycles, fire and chemical attacks. Through the ultrasonic and bending vibration test, the regularity of dynamic elastic modulus changed with the water content of concrete specimens was analyzed in this paper. The results show that the ultrasonic velocity has a low sensitivity to water content when it is below 1.5%. The bending vibration method can better reflect the effect of water content change on dynamic elastic modulus. The regression equation of dynamic elastic modulus and water content was set up by introducing the index function. The research results offer technical reference for the predicting of actual concrete dynamic elastic modulus in different humidity environment.

Abstract: The durability of R.C. structure as a significant indication is widely considered in structure design where the environmental influence research is the basis of study on durability of R.C. structures. The main factors which cause the structure durability degradation are the abbreviation of concrete interface, the concrete quality deterioration and the corrosion of the reinforcing bar. On the basement of comprehensive studies of the current researches on structure durability, the article offers overall reviews and perspective comments on the current durability researches from the aspects of environmental influences, durability analysis methods and structural degradation factors to propose valuable measures for further studies.

Abstract: More and more attentions are paid on reliability and sensitivity of space structure in recently years. To investigate the mechanical characteristics of plane steel truss, OpenSees is utilized to evaluate component and system reliability plane steel truss. Accuracy and efficiency of several reliability approaches are comprehensively compared. Physical property, geometric size of members, and external loads and nodal coordinates are treated as random variable. DDM is utilized to compute sensitivity coefficients of random variables. Finally, bounds on the probability of failure of series systems are estimated according to the KHD bounds.

Abstract: Based on available achievements on carbonation life prediction model of recycled concrete structures at home and abroad, suggested values of recycled coarse aggregate influence coefficient in the practical mathematics model of recycled concrete carbonation depth was put forward through the comparative analysis. Tensile stress influence coefficient in the empirical model of recycled concrete carbonation depth was revised by mathematical regression analysis. The sensitivity analysis for empirical model was undertaken. Results show that the influencing sequence of the carbonation life impact factors of recycled concrete structures is: cover thickness, recycled concrete strength, relative humidity, environment temperature, tensile stress ratio, CO₂ concentration.

Abstract: As for the study on the strain performance of tensile reinforcement under the fatigue loads with amplitude of certain values, two groups of reinforced concrete slab bridge specimen were made. The fatigue test was carried out on one group of specimen, and the corresponding static load test was carried out on another group of specimen, the experimental study on the strain performance of tensile reinforcement was carried on bottom of the mid span of slabs. The results of the study shown that, under the fatigue loads at a certain amplitude, the strain performance of the tensile reinforcement tend to be stable with the increase of number of fatigue cycle, the strain value showed certain linear relationship with static load applied. When the fatigue amplitude increased, the change rule of strain with static load value applied was approximately linear, but the strain value increased more than the fatigue amplitude less under the same static load. It could be seen through the comparison of load - strain curve of the static load specimen, after effect of compressive fatigue with certain amplitude, the strain change with load applied was close to linear change, which has great relationship with the effect on concrete and reinforcement plastic deformation by fatigue load. The test results had the vital significance of further research on reinforcement performance under the action of fatigue loads.

Abstract: The paper introduces life prediction models and existing questions of marine concrete structures exposed to chloride environment; Theory of Box-Jenkins time series prediction method is put forward to analyze the change law of chloride concentration of reinforcemnet surface of marine concrete structures along with time; Stationary test, model identification and parameter estimate are introduced; Modeling process and best model identification are discussed by means of analyzing laws of chloride concentration changing with time, and predicts using the best model. Analysis results show that the prediction model built by Box-Jenkins method has simple form and high prediction accuracy. Whats more, future chloride concentration can be well predicted by history values without determining specific values of durability parameters.This is a new method of life prediction of marine concrete structures.

Abstract: At Present, stress corrosion and corrosion fatigue causing durability degradation of concrete structure in the field of civil engineering become an important problem,and thus become a hot topic to study. But the research on it at home and abroad is still in stage of theoretical exploration. This paper using self-designed corrosion fatigue loading test device, studied in magnesium nitrate solution of concrete under the action of erosion strength increasing regularity, results show that the concrete strength by corrosion fatigue than fatigue specimen attenuation extent.