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- Ay, Lutfi, 1961-
(författare)
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Steel fibrous cement based composites: material and mechanical properties : behavior in the anchorage zones of prestressed bridges
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This PhD thesis is divided into two parts. Part one dealswith the development of the material and the mechanicalproperties of Steel Fibrous Cement Based Composites (SFCBC) forimproving bridge design and construction. It familiarizes thehydration mechanisms of the high performance concrete with thehelp of Powers´ and Jensen´s models. Concretes withdifferent water-cement ratio were compared with each other withrespect to degree of hydration and hydration products. Thisanalysis showed that high performance concrete has higherstrengths not because it has more gel solid, but due to ithaving less porosity and higher filler content compared toordinary concrete.A number of experiments were performed to achieve a mixdesign method for a SFCBC, which has good workability, highearly and long-term strength and good durabilitycharacteristics. A Self-compacting and self-leveling fibrouscomposite, which has ultra high strengths (Compressive strengthfc= 180 ~ 220MPa and flexural tensile strengthfföi= 14 ~ 32MPa depending on the volumefraction of fibers) was produced. This composite was alsotested under different curing conditions in order toinvestigate the effect of curing on hydration andself-desiccation shrinkage. These tests showed that SFCBCshould not be water-cured under a long period andself-desiccation influences the compressive strengthnegatively. Test of scaling at freezing showed that SFCBC hasvery good durability characteristics.Part two deals with the behavior of SFCBC in the anchoragezones of prestressed bridges. The prismatic composite specimenswere tested for different volume fractions of fibers underdifferent concentrations ratios of strip loading. The resultsof these tests showed that the ultimate strength of the SFCBCspecimens was approximately twice that of ordinary concretewith the same size (fc= 60MPa reinforced with stirrups). Therefore,SFCBC has good possibility to replace the traditional rebars inthe anchorage zones of prestressed bridges.This composite has different behavior than the traditionalconcrete e.g. crack formation, failure criteria, effectivestrength and angle of friction. A vertical crack on thecenterline was occurred while wedge developed under the loadingplate. In contrast to ordinary concrete, the cracks could notreach to the bottom of the blocks.The tests results gave the ideas of that this material actslike metals or plastics in the high fiber content. Thismaterial is neither very brittle as concrete nor very ductileas metals but it is somewhere between them.Upper-bound plasticity solutions were utilized for modelingthe bearing capacity of SFCBC. Predictions of this method aregood enough to estimate the bearing capacity of SFCBC in theanchorage zones of prestressed bridges.Keywords:Process improvement of bridges, Prestressedconcrete, High performance concrete, Ultra high performanceconcrete, Hydration, Cement based composites, Fibers,Self-compacting concrete, Bearing capacity, Anchorage zones,Tests
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- Edlund, Stefan
(författare)
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Buckling of T-section beam-columns in aluminium with or without transverse welds
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with buckling of T-section beam-columns inaluminium with or without transverse welds. Totally 26 unweldedand 39 transversely welded T-section beam-columns were tested.Five of the welded beams were clamped. All unwelded and therest of the welded beams were simply supported for bending. Thewelding affects the load-carrying capacity of the beam-columns,because it introduces a heat-affected zone with reducedstrength. All beam-columns had the same theoreticalcross-section dimensions. The thickness of the flange and theweb was 6 mm. The depth and the width were 60 mm. Thetheoretical beam lengths were 500, 1020 and 1540 mm,respectively. Tensile tests of both the parent and theheat-affected material were made in order to determine thematerial properties.Comparisons were made between the buckling tests and threecodes, the European aluminium code Eurocode 9, the Britishaluminium code BS 8118 and the Swedish steel code BSK. Someinterpretations of the codes had to be made, because the codesare not totally clear when applied on T-sections. Most problemsare related to the fact that the section modulus is not thesame for the two edges. In the interaction formulas, only theedge in compression was considered when the bending momentcapacity was calculated. The chosen interpretation of the codeswas often very conservative when compared with the bucklingtests.The general-purpose finite element program Abaqus was usedto develop numerical models of the tested beam-columns. Shellelements were used. The models were calibrated with the resultsfrom the buckling tests. The stress-strain curves used in thefinite element calculations were obtained from the tensiletests. The results of the finite element calculations weresatisfactory. The numerical models could predict the loadcarrying capacity accurate enough. A similar deformed shape ofthe tested and calculated beam-columns was also obtained.Different modifications of Eurocode 9 were analysed in orderto improve the results. One modification was that the ultimatestrength of the heat-affected zone was used instead of theyield strength of the parent material whenthe bucklingreduction factors of a welded section were calculated. Thecalculation of the bending moment capacity in the interactionformulas was also modified. The plastic section modulus wasused to calculate the bending moment capacity when the tip ofthe web was in tension. When the bending moment acted in theopposite direction, the calculation of the bending momentcapacity was based on a modified classification of the webelement. The investigation in this thesis indicates thatEurocode 9 is too severe in the classification of thecross-section. The way the bending moment capacity iscalculated for unsymmetric cross-sections in the interactionformulas needs to be further analysed. Tensile failure at thetip of the web was also discussed. This thesis shows that thecodes need to be improved when it concerns unsymmetriccross-sections. Some information how Eurocode 9 can be improvedis given.Keywords: Buckling, buckling tests, Eurocode 9, aluminiumbeam-columns, beam-columns, T-sections, finite elementanalysis, transverse welds, codes, unsymmetriccross-sections.
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- Getachew, Abraham, 1970-
(författare)
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Traffic Load Effects on Bridges, Statistical Analysis of Collected and Monte Carlo Simulated Vehicle Data
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Research in the area of bridge design has been and still isconcentrated on the study of the strength of materials andrelatively few studies have been performed on traffic loads andtheir effects. Traffic loads have usually been assumed to begiven in codes. This is mainly because it is very difficult tomodel traffic loads in an accurate manner because of theirrandomness.In this work, statistical evaluations of traffic loadeffects, obtained from real as well as Monte Carlo (MC)simulated vehicle data, are presented. As the dynamiccontribution of the vehicle load was filtered by the systemused for measuring vehicle weight, no attention was paid in thepresent study to the dynamic effects or the impact factor. Thedynamic contribution of the traffic load models from codes wasdeducted wherever they were compared with the result from theevaluation of the real data. First, the accuracy of thecollected data was investigated. This was done to examine theinfluence of what was most probably unreasonable data on thefinal evaluated results. Subsequently, the MC simulationtechnique, using a limited amount of the collected data, wasused to generate fictitious vehicle data that could representresults from field measurements which would otherwise have tobe recorded under a long period. Afterwards, the characteristictotal traffic loads for bridges with large spans weredetermined by probabilistic analysis. This was done using realas well as simulated data and the two were compared. Theseresults were also compared with the corresponding valuescalculated using the traffic load model from the Swedish bridgedesign code.Furthermore, using traffic data, different load effects onbridges (girder distribution factor of slab-on-girder bridgesand the mid-span deflection as well as the longitudinal stressat critical locations on box-girder bridges) were investigated.The main task was to obtain a more accurate knowledge oftraffic load distributions on bridges as well as their effectsfor infrastructure design. The results showed that the trafficload models from codes gave considerably higher load effectscompared to the current actual traffic load effects. Theseinvestigations were based on the available data for the actualposition of the vehicles on a single bridge and might not coverall possible traffic scenarios. The results showed only how thereal traffic loads, under”normal”conditions andtheir transverse positions relate to the load model accordingto the codes.KEYWORDS:bridge, traffic load, load effect, transversedistribution, characteristic value,weigh in motion, MonteCarlo simulation, Rice’s formula, level crossinghistogram, vehicle queue.
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- Getachew, Abraham
(författare)
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Trafiklaster på broar : Analys av insamlade och Monte Carlo genererade fordonsdata
- 2000
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis begins with the description of background ,aims and goals of the project. Afterwards, a brief explanation of the probability theory and some probabilistic distribution functions that are used in this work are given.Then the concept of structural reliability is explained. Subsequently the meaning of Monte-Carlo simulation technique in relation to this workis described. Traffic load models given indifferent codes cannot be used directly for the design of long-span bridges, i.e.bridges with span lengths larger than 200 meters. For the determination of the characteristic load values for such bridges, the Swedish National Road Administration (Vli.gverket) conducted traffic load measurements in five different locations in Sweden. All measurement data of course contain errors. Therefore, the collected data from one of the measurement series are investigated in this work. The investigation shows that among the collected data there are vehicles that are registered with unreasonable lengths or/and weights. Totally about 10% of the whole collected data are considered to be inaccurate and should be excluded before further analyses of the vehicle data. About 10%,of the whole collected data, are vehicle dataregistered with one axle. Because of the limited information, these vehicles could not be identified and therefore are not excluded. The characteristic and design traffic load values for different queue lengths are calculated using vehicle data both before and after filtration of inaccurate data. The results hows that the influence of inaccurate data is insignificant. The largest difference between characteristic load values calculated before and after filtration of inaccurate data is 3,5%. Comparing the characteristic as well as the design traffic load values with corresponding values according to BRO 94 shows that the code values are considerably higher than the actual values. In this work, the Monte-Carlo simulation technique is also used to generate vehicle data. The simulated vehicle data show good agreement with the collected data. Afterwards, the probability distribution functions from the simulated as well as the collected vehicle data are calculated and compared. The result shows that the probability distribution functions agree well specially for grater queue weight values.
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- James, Gerard, 1961-
(författare)
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Analysis of traffic load effects an railway bridges
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this thesis studies the load and loadeffects of traffic loads on railway bridges. The increasedknowledge of the traffic loads, simulated using fieldmeasurements of actual trains, are employed in a reliabilityanalysis in an attempt at upgrading existing railwaybridges.The study utilises data from a weigh-in-motion site whichrecords, for each train, the train speed, the loads from eachaxle and the axle spacings. This data of actual trainconfigurations and axle loads are portrayed as moving forcesand then used in computer simulations of trains crossing twodimensional simply supported bridges at constant speed. Onlysingle track short to medium span bridges are considered in thethesis. The studied load effect is the moment at mid-span. Fromthe computer simulations the moment history at mid-span isobtained.The load effects are analysed by two methods, the first isthe classical extreme value theory where the load effect ismodelled by the family of distributions called the generalisedextreme value distribution (GEV). The other method adopts thepeaks-over-threshold method (POT) where the limiting family ofdistributions for the heights to peaks-over-threshold is theGeneralised Pareto Distribution (GPD). The two models aregenerally found to be a good representation of the data.The load effects modelled by either the GEV or the GPD arethen incorporated into a reliability analysis in order to studythe possibility of raising allowable axle loads on existingSwedish railway bridges. The results of the reliabilityanalysis show that they are sensitive to the estimation of theshape parameter of the GEV or the GPD.While the study is limited to the case of the ultimate limitstate where the effects of fatigue are not accounted for, thefindings show that for the studied cases an increase inallowable axle load to 25 tonnes would be acceptable even forbridges built to the standards of 1940 and designed to LoadModel A of that standard. Even an increase to both 27.5 and 30tonnes appears to be possible for certain cases. It is alsoobserved that the short span bridges ofapproximately fourmetres are the most susceptible to a proposed increase inpermissible axle load.Keywords:bridge, rail, traffic load, load effect,dynamic amplification factor, extreme value theory,peaks-over-threshold, reliability theory, axle loads, fielddata.
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- Löfsjögård, Malin, 1972-
(författare)
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Functional Properties of Concrete Roads - Development of an Optimisation Model and Studies on Road Lighting Design and Joint Performance
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The roads constitute a major part of the nation’sinfrastructure. For the society and the individuals it isimportant with a well functioning road network. To sustain theimpact from traffic intensity and heavy loads durable pavementsare demanded. Concrete pavements for roads with high trafficintensity and heavy loads are common in the USA and in severalEuropean countries. In Sweden, less than 1 % of the roadnetwork consists of concrete roads.The research about concrete road pavements has been focusingon development of design methods and studies of surfaceproperties like friction, longitudinal evenness, wearresistance and noise. To increase the knowledge and use ofconcrete roads there is a need to optimise the differentfunctional properties with regard to each other and to socialfactors.The objective of this doctoral thesis is to survey, analyseand quantify relationships between functional properties ofconcrete roads and social factors such as environmental impact,traffic and user safety, riding comfort and economicconsiderations (costs). The goal is to develop a model that canbe used as an instrument for optimising the concrete roaddesign.This thesis describes a thorough literature investigation,special studies on road lighting design of concrete pavements,laboratory investigations about saw-cutting times for jointsand bonding properties of dowels and development of anoptimisation model. The literature investigation has resultedin compiled knowledge on functional properties of concreteroads and their relationships with social factors. A compiledanalysis has also been performed from follow-ups of the fourconcrete roads constructed in Sweden in the 1990s. From thespecial study on road lighting design, proposals are made forusing new values for brightness and specularity and changingthe classification of wet concrete pavements. Theinvestigations of joint performance have given recommendationsfor the earliest saw-cutting time for joints in concrete roads.An optimisation model is proposed, and presently parts of themodel can be used for economic comparisons between differentalternatives.The proposed model needs further research regardingvaluation of the relationships before the model can be used asa total model. Other areas interesting for further researchare: road lighting design and especially wet pavements, upperbound of sawcutting time for joints and further analysis ofdowel performance.
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- Wiberg, Anders, 1971-
(författare)
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Strengthening of concrete beams using cementitious carbon fibre composites
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The research described in this thesis deals with the use ofcement-based carbon fibre reinforced composites forstrengthening of existing structural concrete. There is a large world-wide need for simple and reliablemethods to repair and strengthen aging infrastructure andbuildings. The use of cementitious fi- bre composites offersseveral advantages over the existing methods. No other work onstrengthening of structural concrete with cementitiouscomposites reinforced with continuous high strength fibres wasidentified when the present work started in 1998. At presenttime, 2003, it still is a new technique and very littleresearch has been internationally reported. This work includesa literature survey describing the state of the art of thestrengthening of structural concrete with cement based fibrereinforced composites. Due to the novelty of this technique no specially adaptedmaterials are available and ready for use in cementitiouscomposites. In order to make many small scale tests to optimizethe composite, a new test beam has been developed. Severalparameter studies have been done in this work to determine howdifferent parameters, for example fineness of grading of thecement, additives, and fibre configuration affect thecomposite. Large scale tests of ordinary concrete beams strengthenedwith a cementitious fibre composite are reported. The compositeused was made of a polymer modified mortar and a unidirectionalsheet of continuous carbon fibres, applied by hand. Bothflexural strengthening and shear strengthening were tested. Arelatively new method for measuring strains with digitalcameras was used on the shear strengthenings with a goodresult. It is concluded that the large scale tests have proventhat this method works and has great potential for futureuse. Design methods for strengthenings were studied andevaluated. It is concluded that design methods formulated forstrengthening of structural concrete with carbon fibrereinforced polymers can be adapted also to cementitiouscomposites by introducing an efficiency factor.
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