Methodology for condition assessment and retrofitting of railway bridges

Railway lines consist of steel truss bridges which are very old and have many problems due to inadequate maintenance system or need to increase its capacity to carry higher loads. To undertake above challenges there should be proper procedure to evaluate these bridges. This paper represents methodology for condition assessment and retrofit existing railway bridges. It start from basic condition assessment and runs up to developing detailed numerical model and at the end suitable methods is proposed to retrofit the bridge to full fill the requirements. All major steps were briefly described and all other important facts are mentioned

A Multiaxial fatigue model for steel joints

This paper presents a new model to estimate multiaxial high cycle fatigue life of steel joints, when it is subjected to variable amplitude proportional loadings. The considered failure mechanism of proposed model is in mesoscopic scale (grain scale). The model mainly consists of a new damage indicator, which gives a better prediction to fatigue life than existing fatigue models. The verification of the proposed fatigue model is performed by comparing the experimental fatigue lives with theoretical predictions. It is shown that the proposed multiaxial fatigue model gives much more realistic fatigue life than previous models in both variable amplitude and random loading conditions. Finally, proposed model is applied to estimate fatigue life of a steel joint and associated procedure is clearly indicated

A new approach for predicting the fatigue strength of steels and aluminum alloys in high & giga cycle regimes

Since 1990s various methods have been proposed by researchers to estimate the fatigue strengths of metals at gigacycle fatigue regime (number of cycles > 108). As testing of metals in the gigacycle regime requires much time and sophisticated equipment, obtaining experimental fatigue strengths at gigacycle regime is difficult. Therefore, fatigue strength prediction methods are very important. However, the available prediction methods are complicated and require parameters which are not easily tested. Therefore, it is necessary to discover simple but reliable prediction methods that require few and easily obtainable material parameters. In this study, a new model for predicting the fatigue strength of steels at high and gigacycle fatigue regimes is first proposed. A good global relationship between the ultimate tensile strength, the fatigue strength and the number of cycles to failure is obtained after analyzing more than 80 heats of experimental results of 45 steels and 9 aluminium alloys. Using this global relationship, secondly, a model is proposed for predicting the fatigue strength of steels and alloys

Reconstruction vs retrofitting of a bridge for sustainability

Bridges face the risk of being damaged by natural and manmade disasters. Old bridges are more vulnerable in such situations. The common practice is removing these damaged bridges and constructing new ones. However, repairing, retrofitting and reusing damaged bridges could be economical and less time consuming and hence more sustainable than building new bridges. There are various methods to assess the possibility of improving old and / or damaged bridges using modern day techniques. This paper is a case study for using one of such assessment procedures on a damaged railway bridge in Puttalam, Sri Lanka. The bridge concerned is 34m long, single spanned, double lattice girded, wrought iron Railway Bridge, which was built about 40 years ago and damaged and displaced from its abutments by floods. The paper discusses the method used to determine the possibility of reusing the bridge by conducting a series of tests on the temporarily erected bridge and using a finite element model. It also presents results of tests carried out after the bridge was repaired and retrofitted. The results show that retrofitting has made substantial improvements to the bridge

Evaluation of Community Resilience Aspects of Sri Lankan Coastal Districts

This research is carried out to evaluate important community resilience aspects of coastal districts in Sri Lanka and to provide suitable recommendations to strengthen them. After carrying out an indepth literature survey and interviewing key personnel who are involved in the field of Disaster Management and Disaster Risk Reduction, existing status of the coastal hazards, multi-hazard assessments, early warning mechanisms, national policies, guidelines and efforts and regional cooperation were identified. During the literature survey, it was observed that Sri Lanka has developed a Hazard profile for the country and has an Early Warning Dissemination System which seems to function quite well by the book. What is more, the country is in the process of orienting the existing national policies and guidelines with the post 2015 global standards such as the Sendai framework and Sustainable Development Goals. Sri Lanka being a member of Indian Ocean Tsunami Warning and Mitigation System (IOTWMS) and Regional Integrated Multi-Hazard Early Warning System for Africa and Asia (RIMES) depicts that the country has a good regional cooperation in terms of Early Warning. Even though Sri Lanka lacks efficient and sustainable resilience mechanisms focused on the coastal communities, national efforts are underway to build up the coastal resilience. Training and public awareness campaigns, efficient funds, properly maintained hierarchy and concern to the coastal ecosystems are some of the enablers identified in this study which are associated in building coastal resilience. Developing and updating a multi-hazard map, improving the interagency cooperation and driving towards a people-centred Multi-Hazard Early Warning System (MHEWS) are some of the recommendations given after the analysi

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

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

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

Tsunami damaged buildings assessment using high-resolution satellite imagery, GIS & GPS data

This paper presents a methodology and results of evaluating damaged building extraction using an object recognition task based on Differential Morphological Profile (DMP) for Very High Resolution (VHR) remotely sensed images. The proposed approach involves several advanced morphological operators among which an adaptive transforms with varying size, shape and gray level of the structuring elements. IKONOS-2 Satellite images consisting of pre and post 2004 Indian Ocean Tsunami site of Kalmunai area in east cost of Sri Lanka were used. Morphological operation of opening and closing by constructions using structural element are applied for segmented images, then derivative of the opening profile is defined as the vector. ISODATA algorithm is used for the feature extraction and the results comparison with ground truth data. This result appeared to have high accuracy, the confidence measures produced of completely destroyed structure gives 60% and 86% by object base and pixel base respectively after the tsunami in one segment of Maruthamunai GN Division

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