Deterioration prediction of bridge by Markov chain model and Bayesian theory

This manuscript presents a bridge deterioration prediction method by using Markov chain model and Bayesian theory. Markov chain model works by defining discrete condition states and accumulating the probability of transition from one condition state to another over discrete time intervals. The probability of transition is generally expressed by the matrix. Though the previous studies have predicted the bridge deterioration by developing deterioration curves by using the Markov chain model, the predicted value will not be necessarily suitable for the measured value in the future. Therefore, this study demonstrates a method to predict deterioration progress as a prediction interval by taking account of the uncertainty by the Monte Carlo simulation. In addition, the method to update the prediction interval after the inspection is developed by Bayesian theory. This research was developed by using inspection results of existing bridges in Japan, and the proposed mechanism is convenient for bridge engineers to take rational decisions on the maintenance management plan of steel bridge infrastructures

A simple fracture criterion to predict failure of steel Structures in extremely-low cycle fatigue region

This paper presents a simple criterion to predict the failure of steel structures due to the interaction effect of fracture and fatigue which is termed as extremely-low cycle fatigue (ELCF) failure. The criterion has been obtained from further simplification of available cyclic void growth model (CVGM). Initially the simplified ELCF fracture criterion is clearly presented and associated ELCF fracture prediction methodology is also indicated. The simplified criterion is then employed to determine ELCF fracture of some structural models. Hence verification of the simplified criterion is confirmed by comparing the results with previous criterionbased estimations. Then the simplified criterion is applied to predict the ELCF fracture of a reduced beam section specimen. Finally, study tends to conclude that the simplified criterion produces reasonable accurate prediction to ELCF fracture of steel structures where magnitude of triaxiality remains relatively constant

Fatigue life prediction of bridges considering the effect of Multiaxial stresses

This paper presents a new low cycle fatigue model to predict life of steel bridges. It consists of Coffin-Manson strain-life curve with a new strain based damage index. The damage variable is based on a modified von Mises equivalent strain to account for effects of loading non-proportionality and strain path orientation in low cycle multiaxial stress state. The proposed model was verified by comparing with experimental test results of two materials. Then, it was applied an existing riveted wrought iron railway bridge to estimate fatigue life due to usual traffic and earthquake loadings. The obtained results verify the importance and effectiveness of the proposed model over commonly used Miner’s rule model in fatigue life estimation of steel bridges

Combined high and low cycle fatigue model for prediction of Steel bridge lives

A new fatigue model is presented to predict life of steel bridges for combined high and low cycle fatigue. It consists of a modified strain-life curve and a new strain based damage index. The damage variable is based on a modified von Mises equivalent strain to account for effects of loading non-proportionality and strain path orientation in multiaxial stress state. The proposed model was verified with experimental test results of two materials, available in the literature. Then, the proposed model was applied to a wrought iron railway bridge to estimate the fatigue life due to usual traffic and earthquake loadings. The obtained results confirm the importance and effectiveness of the proposed model over commonly used Miner’s rule based life prediction of steel bridges

Numerical study on remaining strength prediction of corroded Steel bridge plates

Corrosion causes strength deterioration of aged steel infrastructures and hence careful evaluation of their remaining load-carrying capacities are of high importance in maintenance engineering. To develop a more reliable strength estimation technique, only experimental approach is not enough as actual corroded surfaces are different from each other. However in modern practices, numerical simulation is being used to replace the time-consuming and expensive experimental work and to comprehend on the lack of knowledge of mechanical behavior, stress distribution, ultimate behavior and so on. Therefore, using of numerical analysis method will give important knowledge not only for strength estimation but also for subsequent repair and retrofitting plan. The results of non-linear FEM analysis of many actual corroded plates with different corrosion conditions and comparison of them with the respective tensile coupon tests results are presented in this paper. Further, the feasibility of establishing of an analytical methodology to predict the residual strength capacities of a corroded steel member with fewer number of measuring points are also discussed

Effects of corrosion on degradation of tensile strength of steel bridge members

Evaluation of existing steel bridges becomes vital due to natural aging, increasing load spectra, deterioration caused by corrosion, increasing seismic demand, and other problems. In the result, bridge structures exposed to aggressive environmental conditions are subjected to time-variant changes of resistance. Corrosion becomes one of the major causes of deterioration of steel bridges and there have been many damage examples of older steel bridge structures due to corrosion around the world during past few decades. Controlling corrosion on bridge structures can prevent premature failure and lengthen their useful service life, both of which save money and natural resources, and promote public safety. Therefore, understanding of the influence of damage due to corrosion on the remaining load-carrying capacities is a vital task for the maintenance management of steel highway infrastructures. But at the moment, number of steel railway and highway bridge infrastructures in the world is steadily increasing as a result of building new steel structures and extending the life of older structures. Therefore, it would be an exigent task to measure several thousands of points, to accurately reproduce the corroded surface by numerical methods and to predict the behaviour of that corroded member more precisely. So, there is a need of more brisk and accurate assessment method which can be used to make reliable decisions affecting the cost and safety. Therefore, this paper presents the analytical results of many actual corroded steel members and comparison of them with their respective experimental results. Further, a simple and reliable analytical method by measuring only the maximum corroded depth (tc,max) is proposed, in order to predict the residual strength capacities of corroded steel plates more accurately

Maintenance strategy for bridges using reliability concept and analytical hierarchy process

Civil infrastructure in most of countries is getting old and therefore, there is a tremendous need to assess their safety levels. Among civil infrastructure, bridges are one of the main components and there is a need to study more on their safety and durability to minimize the maintenance cost and to avoid sudden failures. This paper presents bridge maintenance strategy which consists of two parts: (1) reliability based condition assessment procedure and; (2) analytical hierarchy process (AHP) based resources prioritization. In reliability based assessment, safety margins are initially proposed depending on the types of bridges. It is assumed that load and strength are random variables. Elementary reliability indices and thereby elementary failure probabilities are estimated for each safety margins. Then, system failure probability of the bridge is calculated for the time of consideration. Finally, this system failure probability is used to get system reliability index of the bridge and it is used as an index to express the condition of the bridge for the considered time. Secondly, AHP is implemented to identify the order of resources prioritization among set of bridges. The selected criteria are safety, cost of maintenance actions and relative importance of the bridge. Relative importance varies depending on historical importance, age and route of bridge location. The proposed methodology is applied to a collection of five bridges in Sri Lanka to estimate their safety levels and resources prioritization in bridge maintenance

Pioglitazone Prevents Capillary Rarefaction in Streptozotocin-Diabetic Rats Independently of Glucose Control and Vascular Endothelial Growth Factor Expression

Background/Aims: Reduction of capillary network density occurs early in the development of metabolic syndrome and may be relevant for the precipitation of diabetes. Agonists of the peroxisome proliferator-activated receptor (PPAR)-gamma transcription factor are vasculoprotective, but their capacity for structural preservation of the microcirculation is unclear. Methods: Male Wistar rats were rendered diabetic by streptozotocin and treated with pioglitazone in chow for up to 12 weeks. Capillary density was determined in heart and skeletal muscle after platelet endothelial cell adhesion molecule-1 (PECAM-1) immunostaining. Hallmarks of apoptosis and angiogenesis were determined. Results: Capillary density deteriorated progressively in the presence of hyperglycemia (from 971/mm(2) to 475/mm(2) in quadriceps muscle during 13 weeks). Pioglitazone did not influence plasma glucose, left ventricular weight, or body weight but nearly doubled absolute and relative capillary densities compared to untreated controls (1.2 vs. 0.6 capillaries/myocyte in heart and 1.5 vs. 0.9 capillaries/myocyte in quadriceps muscle) after 13 weeks of diabetes. No antiapoptotic or angiogenic influence of pioglitazone was detected while a reduced expression of hypoxia-inducible factor-3 alpha and PPAR coactivator-1 alpha (PGC-1 alpha) mRNA as well as vascular endothelial growth factor (VEGF) protein possibly occurred as a consequence of improved vascularization. Conclusion: Pioglitazone preserves microvascular structure in diabetes independently of improvements in glycemic control and by a mechanism unrelated to VEGF-mediated angiogenesis. Copyright (C) 2012 S. Karger AG, Base