Browsing by Author "Dissanayake, PBR"

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Behaviour of cantilever slabs in blast environment and strengthening techniques
(2013-11-13) Bandara, AMACS; Dissanayake, PBR
Cantilever slabs are among the most vulnerable structural elements at blast loading. As they are indispensable to most structures, it is important to investigate the behaviour of cantilever slabs in a blast environment and possibilities of improving their blast resistant abilities. In this paper we are proposing simplified design envelopes drawn for steel to concrete ratio and effective depth of slabs against blast parameters for a common range of cantilever slabs. These design envelopes have been prepared using results of previous research. Using these envelopes, conclusions are made about the effect of slab thickness which is one of the major parameters for improving blast resistant ability. This paper also discusses the blast resistant ability of reinforced concrete cantilevers designed by using the code BS8110 and ways to improve such conventional designs to make them better resistant in a blast loading environment in an economical way.
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Combined high and low cycle fatigue model for prediction of Steel bridge lives
(2013-11-15) Ohga, M; Karunananda, K; Dissanayake, PBR; Siriwardane, SASC
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.
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Effects of corrosion on degradation of tensile strength of steel bridge members
(2013-11-30) Appuhamy, JMRS; Ohga, M; Chun, P; Furukawa, S; Dissanayake, PBR
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.
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Enhanced effective thickness for remaining strength estimation of corroded steel bridge members
(2013-11-07) Appuhamy, JMRS; Ohga, M; Chun, P; Dissanayake, PBR
Infrastructure plays a major role in the economy of a country. Bridges are a major component of any infrastructure and the failure of a bridge will affect the economy of any country. Over the past decades there have been many damage examples of older steel bridge structures due to corrosion around the world. Exposure of a steel structure to the natural environment and inadequate maintenance will cause corrosion and leads to impairment of its operation. Efficient maintenance, repair and rehabilitation of existing bridges require the development of a methodology that allows for an accurate evaluation of load carrying capacity and prediction of remaining life. Therefore, careful evaluation of remaining load-carrying capacities of corroded steel bridge structures is of high importance in transportation and maintenance engineering. Even though there are some published methods to assess the strength reduction due to corrosion of bridges, all of them were developed by using specimens with about 30mm width. However during the preliminary investigation, it was found that many corrosion pits with more than 30mm diameters exist in actual severe corroded members. So, the influence of such corroded conditions could have been neglected and hence their actual remaining strengths might be different than those were obtained from those experimental studies. Therefore, this paper investigates the effect of actual corroded conditions on their remaining strength capacities and proposes a simple, efficient and accurate residual strength estimation method by using an enhanced effective thickness parameter with the correlation of maximum corroded depth, which can be used for the maintenance management of aged steel bridge infrastructures.
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Evaluation of tensile strength deterioration of steel Bridge plates due to corrosion
(2013-11-15) Ohga, M; Appuhamy, JMRS; Kaita, T; Fujii, K; Dissanayake, PBR
Over the past decades there have been many damage examples of older steel bridge structures due to corrosion around the world. Even though there are some published methods to assess the strength reduction due to corrosion of bridges, it is hard to find any with lesser number of measuring variables which eventually accounts for the accuracy and the convenience of the investigation for adequate bridge management. So, in this study, a simple method of calculating the remaining yield and tensile strength by using a concept of representative effective thickness (teff) with correlation of initial thickness (t0) and standard deviation of thickness (σst) is proposed, based on the results of many tensile coupon tests of corroded plates obtained from a steel plate girder used for about 100 years with severe corrosion.
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Fatigue life prediction of bridges considering the effect of Multiaxial stresses
(2013-11-15) Ohga, M; Karunananda, K; Dissanayake, PBR; Adasooriya, AMND
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.
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Fatigue Life Prediction of Steel Bridges with High Amplitude Loadings
(2015-12-29) Karunananda, PAK; Pallewatta, TM; Dissanayake, PBR; Ohga, M; Siriwardane, SASC
Abstract: This paper presents a new fatigue model to predict life of steel bridges considering the effect of high amplitude loading. It consists of a modified strain-life curve and a new strain based damage index. Modified strainlife curve consists of Coffin-Manson relation in low cycle fatigue region and a new strain-life curve in high cycle fatigue region. The damage variable is based on a modified von Mises equivalent strain to account for the 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 on the literature. Then, it was illustrated with an old riveted wrought iron railway bridge. The obtained results verify the effectiveness of the proposed model over commonly used Miner’s rule based life prediction of steel bridges
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Future life evaluation of existing steel bridges
(2013-11-13) Bandara, AMACS; Rathnayaka, RMSUP; Attanayake, AMCTK; Dissanayake, PBR
Bridges play a major role in road networks. Continuous health monitoring and proper maintenance of bridges is required to obtain the maximum service from them. Life evaluation of bridges is part of the health monitoring work, which is usually done when bridges get to the end of their design lives under designed service loading or after accidental situations such as overloading or partial collapse of bridges due to floods, landslide, cyclones, earthquakes, bomb blasts, traffic accidents or after unexpected traffic overloading. Health monitoring and assessing structural soundness of existing bridges is important for making economical decisions on repairing, retrofitting or replacing them. Knowing the future life of existing bridges is important for planning new bridges before the old bridges collapse. This paper describes various methods used for fatigue life evaluation of existing steel bridges, the use of stress-life & strain-life curves and finite element models. It explains the four types of fatigue which occur in structural elements due to different magnitudes of cyclic stresses. It also describes the importance of selecting the appropriate life evaluation method. A case study is given as an example in which some of these techniques were used.
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High performance concrete incorporating fly ash, nano-silica (nano-SiO2) and micro-silica (micro-SiO2)
(2016-01-06) Priyadarshana, MST; Dissanayake, PBR
High performance concrete (HPC) exceeds the properties and constructability of normal concrete. Normal and special materials such as fly ash, micro silica and nano silica are used to make these specially designed concretes that must meet a combination of performance requirements. There are many good reasons to view fly ash, micro silica and nano silica as blended materials in concrete. In many cases, concrete made with fly ash, micro silica and nano silica performs better than concrete made without them. In this paper, an effort was made to evaluate the effect of nano-silica (nano-SiO2), micro-silica (micro-SiO2) and fly ash in improving the properties concrete. Firstly, compressive strength of concrete with different percentage of nano-silica (nano-SiO2), micro-silica (micro-SiO2) and fly ash was studied. Secondly, compressive strength of concrete with Ordinary Portland cement (OPC) and Portland fly ash cement (PPC) was studied. Thirdly, compressive strength of concrete with combination of fly ash and micro silica (micro-SiO2) was studied.
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Maintenance strategy for bridges using reliability concept and analytical hierarchy process
(2013-11-28) Karunananda, K; Ohga, M; Furukawa, S; Dissanayake, PBR; Siriwardane, S
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.
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Methodology for condition assessment and retrofitting of railway bridges
(2013-12-06) Rathnayaka, RMSUP; Dissanayake, PBR
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.
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A Multiaxial fatigue model for steel joints
(2013-12-06) Siriwardane, SASC; Dissanayake, PBR
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.
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A new approach for predicting the fatigue strength of steels and aluminum alloys in high & giga cycle regimes
(2013-11-13) Bandara, AMACS; Dissanayake, PBR; Dissanayake, UI; Siriwardane, SASC
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.
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Novel Method for Developing S-N Curves for Corrosion Fatigue Damage Assessment of Steel Structures
(2015-12-29) Bandara, CS; Dissanayake, UI; Dissanayake, PBR
Abstract: Corrosion is one of the main problems in steel structures. The combined effect of corrosion and fatigue caused by cyclic loading magnifies the damage severely reducing the fatigue life of the structure. Steel bridges in coastal and industrial zones are among the structures most vulnerable to corrosion fatigue. Up until now there have been no accurate methods introduced for assessing corrosion fatigue damage and predicting the future life of structures in a corrosive atmosphere. In the S-N approach based fatigue damage assessment method S-N curves should include corrosion effects. If usual S-N curves that do not include corrosion effects are used, they should be modified or safety factors should be applied to account for the effects of corrosion. The present paper describes a study carried out for improving one of the existing full range S-N curve models for corrosion effects. Using adjustments to the existing S-N model a new corrosion based S-N model was proposed. Experimental results showed that the proposed S-N model can be efficiently used for assessing fatigue damage of steel structures located in corrosive atmosphere. The S-N model proposed remains a simple single formula. The only parameters necessary for the new corrosion based S-N model are the ultimate tensile strength, Vickers hardness and the high cycle fatigue strength in corrosive environment.
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Numerical investigation of future tsunami hazard on Sri Lanka From the earthquakes of Sumatra-Andaman region
(2013-11-15) Ohga, M; Appuhamy, JMRS; Tinti, S; Lai, C; Dissanayake, PBR
The mega event of Indian Ocean Tsunami 26th December 2004, stressed the need for assessing tsunami hazards in vulnerable coastal areas in Sri Lanka. Two major areas of the management of disaster prevention are to evacuate people in the coastal area to safer areas as soon as possible and pre-modification of coastal structures to resist the tsunami waves effectively. Often the only way to determine the potential run-ups and inundation from a local or distant tsunami is to use numerical modeling, since data from past tsunamis is usually insufficient. It then might be possible to use such simulations to predict tsunami behavior immediately after an earthquake is detected. This paper consists of results of the numerical models of 26th December 2004 Tsunami and three other possible Tsunamis in this region which eventually can be used to create inundation and evacuation maps to minimize future damages.
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Numerical study on remaining strength prediction of corroded Steel bridge plates
(2013-11-15) Ohga, M; Appuhamy, JMRS; Kaita, T; Fujii, K; Dissanayake, PBR
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.
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Reconstruction vs retrofitting of a bridge for sustainability
(2013-11-13) Dissanayake, PBR; Bandara, AMACS; Rathnayaka, RMSUP
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.
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A simple fracture criterion to predict failure of steel Structures in extremely-low cycle fatigue region
(2013-11-15) Siriwardane, SASC; Dissanayake, PBR; Ohga, M; Wanniarachchi, KS
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.
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Tsunami damaged buildings assessment using high-resolution satellite imagery, GIS & GPS data
(2013-12-01) Bari, UA; Dinesh, PC; Tamura, M; Dissanayake, PBR
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.