The dominant reinforcement used widely for concrete structures is conventional steel bars (rebars). Nevertheless, the perpetual effort toward evolution and development could not exclude the engineering field, thus new innovative and sophisticated methods are introduced. It is true that, due to lack of extended regulations and standards, the fibre reinforced concrete (FRC) was limited to non-structural applications. However, the last years the situation is changing rapidly and already the applications of FRC include actual structural members. The subject of the current thesis was a tramway’s track slab from “Sparvag City” project in Stockholm. The aim was to evaluate the track slab, in terms of alternative reinforcing ways. In particular three models were examined; model I – conventional reinforcement, model II – steel fibre reinforced concrete (SFRC) and model III – SFRC with conventional reinforcement. The assessment was performed from structural, regulations – compliance, economic and ergonomic perspective. A static linear analysis of the track slab was performed using Abaqus; a finite element analysis (FEA) software. The track slab was subjected only to mechanical loads (selfweight and traffic actions) and thus, the design internal forces were extracted. Thereafter, Eurocode 2 (EN 1992-1-1, 2004) and Swedish standards for FRC structures (SS 812310:2014) were utilized for the reinforcement design of the models. The design was performed in ultimate limit state (ULS), for bending moment and shear resistance, and in serviceability limit state (SLS), for stress limitation and crack control. Model I and III were successfully designed abiding with the respective regulations and requirements, while “only fibres” model was considered valid only for bending moment resistance according to SS 812310:2014. Consequently only models I and III were compared with each other. From the economic comparison it was obtained that model I was less expensive than model III, but on the other hand its construction time was larger. Furthermore model III contained significantly less total rebars’ mass in comparison to model I. This particularity was crucial for the ergonomic assessment. The human factors, that were relevant to the ergonomic assessment, improved the quality of the comparison and the extracted inferences, but also introduced aspects impossible to be put against economic facts as an equal quantity. Thus, there was not a final proposal as the best solution for the thesis subject. / Armeringen av betongkonstruktioner domineras av konventionell armering (armeringsjärn). Med den ständiga strävan mot utveckling och förbättring har inom teknikområdet nya innovativa och avancerade metoder introducerats. Det är på grund av bristen på normer, standarder som fiberarmerad betong begränsats till icke- bärande ändamål. Däremot har situationen förändrats under de senaste åren, redan idag kan man se konstruktioner där fiberarmering används till bärande ändamål. Amnet for den aktuella masterexamen var betongplatta i projektet ”Sparvag City” i Stockholm. Syftet var att utvärdera betongplattan, i form av att undersöka alternativa armeringsmöjligheter. I synnerhet undersöktes tre modeller; modell I- konventionellt armerad platta, modell IIstålfiberarmerad platta och modell III stålfiberarmerad platta kombinerad med konventionell armering. Modellernas möjligheter att uppfylla regelverkens krav undersöktes, men de jämfördes även ur ekonomiskt samt ergonomiskt perspektiv. En statisk linjär analys av betongplattan genomfördes i ett finit element program, Abaqus. Betongplattan utsattes för mekanisk belastning (egenvikt samt trafiklast) för vilken dimensionerande krafter extraherats. Därefter användes Eurocode 2 (EN 1992-1-1, 2004) och den svenska standarden för fiberarmerade betong konstruktioner (SS 812310:2014) för vidare konstruktionsberäkningar. Konstruktionsberäkningarna för betongplattan genomfördes i brottgränstillstånd för böjmoment samt tvärkraft, i brukgränsmotståndet undersöktes betongplattan för spänningsbegränsningar samt sprickkontroll. Konstruktionsberäkningarna kunde genomföras för modell I och III med de existerande föreskrifterna och kraven, men modellen med ”endast fibrer” kunde endast dimensionerna för böjmoment enligt SS 812310:2014. Därför kunde endast modell I och III fortsättningsvis jämföras med varandra. Från den ekonomiska jämförelsen erhölls det att modellen I var billigare än modell III, men att konstruktionstiden var längre. Dessutom var behoven för konventionell armering (armeringsjärn) betydligt mindre för modell III till skillnad från modell I. Modellernas innehåll av konventionell armering var avgörande för den ergonomiska bedömningen. Den mänskliga faktorn, som var relevanta för den ergonomiska bedömningens, gav jämförelsen av modellerna en annan dimension, där de viktiga mänskliga faktorerna

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Research in concrete has advanced to such an extent that it is now possible to add steel fibres to concrete in order to improve its durability and ductility. This led to a research group in Europe, FIB, who has provided guidelines to designing Steel Fibre Reinforced Concrete (SFRC) structures. They have found that it is possible for SFRC beams in flexure to be in static equilibrium. However, the time-dependent behaviour of SFRC has not been researched fully and it requires further investigation. When looking at a concrete beam in flexure there are two main stress zones, the compression zone and the tension zone, of which the tensile zone will be of great interest. This study will report on the investigation of the tensile time-dependent behaviour of SFRC in order to determine how it differs from conventional concrete. The concrete has been designed specifically to exhibit strain-softening behaviour so that the material properties of SFRC could be investigated fully. Factors such as shrinkage and tensile creep of SFRC were of the greatest importance and an experimental test setup was designed in order to test the tensile creep of concrete in a simple and effective manner. Comparisons were be made between the tensile creep behaviour of conventional concrete and SFRC where emphasis was placed on the difference between SFRC specimens before and after cracking occurred in order to determine the influence of steel fibre pull-out. The addition of steel fibres significantly reduced the shrinkage and tensile creep of concrete when un-cracked. It was however found that the displacement of fibre pull-out completely overshadowed the tensile creep displacements of SFRC. It was necessary to investigate what effect this would have on the deflection of SFRC beams in flexure once cracked. Viscoelastic behaviour using Maxwell chains were used to model the behaviour of the tensile creep as found during the tests and the parameters of these models were used for further analyses. Finite Element Analyses were done on SFRC beams in flexure in order simulate creep behaviour of up to 30 years in order to determine the difference in deflections at mid-span between un-cracked and pre-cracked beams. The analyses done showed that the deflections of the pre-cracked SFRC beams surpassed the requirements of the Serviceability Limit States, which should be taken into account when designing SFRC beams. / AFRIKAANSE OPSOMMING: Die navorsing in beton het gevorder tot so ‘n mate dat dit nou al moontlik is om staal vesels by die beton te voeg sodat dit beton se duursaamheid en duktiliteit te verbeter. Dit het gelei tot ‘n groep in Europa, FIB, wat dit moontlik gemaak het om Staal Vesel Beton (SVB) strukture te ontwerp. Hulle het gevind dat dit moontlik is vir SVB balke om in statiese ewewig te wees tydens buiging. Die tyd afhanklike gedrag van SVB is egter nog nie deeglik ondersoek nie en benodig dus verdure ondersoek. Wanneer ‘n balk in buiging aanskou word kan twee hoof spanningzones identifiseer word, ‘n druk zone en ‘n trek zone, waarvan die trek zone van die grootste belang is. Hierdie studie gaan verslag lewer oor die ondersoek van tyd-afhanklike trekgedrag van SVB om te bepaal hoe dit verskil van konvensionele beton. Die beton was spesifiek ontwerp om vervormingsversagtende gedrag te wat maak dat die materiaal eienskappe van SVB ten volle ondersoek kan word. Faktore soos krimp en die trekkruip van SVB was van die grootste belang en ‘n eksperimentele toets opstelling was ontwerp om die trekkruip van beton op ‘n eenvoudige en effektiewe manier te toets. Daar was vergelykings getref tussen die trekkruip gedrag van konvensionele beton en SVP en groot klem was geplaas op die verskil tussen SVB monsters voor en na die monsters gekraak het om te bepaal wat die invloed was van staalvesels wat uittrek. Die byvoeging van staalvesels het beduidend die kruip en trekkruip van beton verminder. Daar was alhoewel gevind dat die verplasing van die uittrek van staalvesels heeltemal die trekkruip verplasings van SVB oorskadu het. Dit was nodig om te sien watse effek dit op die verplasing van SVB balke in buiging sal hê. Viskoelastiese gedrag deur Maxwell kettings was gebruik om die gedrag van trekkruip, soos gevind deur die toetse, te modelleer en die parameters van hierdie modelle was verder gebruik vir analises. Eindige Element Analises was gedoen op SVB balke in buiging om die trekkruip gedrag tot op 30 jaar te simuleer op die verskil tussen die defleksies by midspan tussen ongekraakte en vooraf gekraakte balke te vind. Die analises het gewys dat die defleksies van die vooraf gekraakte balke nie voldoen het aan die vereistes van die Diensbaarheid limiete nie, wat in ag geneem moet word wanneer SVB balke ontwerp word.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Steel fibre reinforced concrete (SFRC) is the most prominent fibre reinforced concrete composite that was engineered to enhance the material’s post-cracking behaviour. In certain situations it is utilised to replace conventional reinforcement and considered to be more cost-efficient. The purpose of this research is to characterise the moment redistribution behaviour of a statically indeterminate SFRC structure with varying volumes of fibres, with the focus on the development of the moment redistribution accompanied by the rotation of the plastic hinges at the critical sections in the structure. The material properties were characterised with a series of experimental tests. The compression behaviour was obtained with uniaxial compression tests while the uniaxial tensile behaviour was obtained with an inverse analysis performed according to flexural test results. These properties were utilised to derive a theoretical moment-curvature relation for each SFRC member which supplied the basis for the characterised moment-rotation behaviour and the finite element analyses (FEA) performed on the statically indeterminate structure. Experimental tests were conducted on the statically indeterminate structure in laboratory conditions to validate the theoretical findings. For the different SFRCs the material properties in compression were similar, while it resulted in an increased tensile resistance with an increase in the volume steel fibres. The theoretical momentcurvature and moment-rotation responses also indicated an increased structural capacity and member ductility with an increase in the volume fibres. From the finite element analyses the computational moment redistribution-plastic rotation relations were obtained. It was found that the final amount of moment redistribution decreased with an increase in the fibre volume, but that the rotational capacity increased. It was found that the experimental moment-curvature and moment-rotation results correlate well with the theoretical predictions. Also, unexpected structural behaviour was observed, but the issue was addressed with applicable computational analyses which confirmed the possible causes. It was concluded that the computational moment redistribution approximations were reasonably accurate. A parameter study indicated that the crack band width differed among the different SFRC members. / AFRIKAANSE OPSOMMING: Staal vesel versterkte beton (SVVB) is die mees vooraanstaande vesel versterkte beton mengsel wat ontwikkel is om die materiaalgedrag na kraakvorming te verbeter. In sekere situasies kan dit gebruik word om konvensionele staal te vervang en lei soms to koste vermindering . Die einddoel van die studie is om die moment herverdeling gedrag te karaktiseer vir ‘n statiese onpebaalbare SVVB struktuur deur die invloed van verskillende volumes vesels en die rotasie kapasiteit by die kritieke posisies in ag te neem. Die materiaal eienskappe was geidentifiseer met ‘n reeks eksperimentele toetse. Die druk gedrag was geïdentifiseer deur eenassige druktoetse, terwyl die eenassige trek gedrag bekom is met die implementasie van ‘n inverse analise van die uitgevoerde buig toetse. Hierdie eienskappe is gebruik om die teoretise moment-kromming verhouding vir elke mengsel te bekom. Hierdie verhoudings word as die basis bestempel vir die teoretiese moment-rotasie verhouding en die eindige element analises (EEA) wat op ‘n staties onbepaalbare struktuur toegepas is. Eksperimentele toetse is op hierdie voorgestelde struktuur toegepas om die teoretiese verwagtings te verifieer. Dit is gevind dat die druk gedrag ooreenstem tussen die verskillende mengsels, alhoewel ‘n toename in die trek kapasiteit ervaar is met ‘n toename in die volume vesels. Die teoretiese momentkromming en moment-rotasie verwantskappe stel ook voor dat die strukturele kapasiteit en duktiliteit toeneem met ‘n toename in die volume vesels. Die teoretiese moment herverdeling-plastiese rotasie verwantskapppe is verkry deur middel van die eindige element analises. Dit is gevind dat die aantal moment herverdeling by faling afgeneem het vir ‘n toename in die volume vesels, maar dat dit to ‘n groter rotasie kapasiteit gelei het. Van die eksperimentele resultate is dit afgelei dat die teoretiese moment-kromming en momentrotasie verwantskappe goeie benaderings voorstel. Sekere invloede van die opstelling het daartoe gelei dat onverwagte strukturele gedrag bekom is, maar die moontlike invloede is verifieer met eindige element analises. Dit is afgelei dat die teoretiese beramings van die moment herverdeling gedrag redelik akkuraat is. ‘n Parameter studie het getoon dat die kraak spasiëring verskil tussen mengsels met verskillende volumes vesels.

The doctoral thesis deals with a non-destructive testing method (NDT) designed to evaluate the uniformity of distribution and determination of the concentration of steel fibres in steel fiber reinforced concrete (SFRC). At present, no non-destructive method is available in the field of diagnostics of building structures to assess the concentration and the homogeneity of SFRC. The Institute of Building Testing (SZK FAST BUT Brno) has several diagnostic devices, but their utility for the evaluation of selected parameters of SFRC has not proven during the research activity. This knowledge led to the design of a new measuring instrument in cooperation with the Institute of Theoretical and Experimental Electrical Engineering of the Faculty of Electrical Engineering and Communication (UTEE FEKT BUT in Brno) and the methodology for evaluation of these parameters. The proposed NDT method has been experimentally tested and verified for its utility for the evaluation of SFRC in building practice.