Yes / This paper presents test results of six full scale reinforced concrete continuous T beams. One beam was reinforced with glass fibre reinforced polymer (GFRP) bars while the other five beams were reinforced with a different combination of GFRP and steel bars. The ratio of GFRP to steel reinforcement at both mid-span and middle-support sections was the main parameter investigated. The results showed that adding steel reinforcement to GFRP reinforced concrete T-beams improves the flexural stiffness, ductility and serviceability in terms of crack width and deflection control. However, the moment redistribution at failure was limited because of the early yielding of steel reinforcement at a beam section that does not reach its moment capacity and could still carry more loads due to the presence of FRP reinforcement. The experimental results were compared with the ultimate moment prediction of ACI 440.2R-17, and with the existing theoretical equations for deflection prediction. It was found that the ACI 440.2R-17 reasonably estimated the moment capacity of both mid-span and middle support sections. Conversely, the available theoretical deflection models underestimated the deflection of hybrid reinforced concrete T-beams at all load stages.

Yes / This paper reports the testing of five reinforced concrete continuous beams strengthened in flexure with externally bonded carbon-fibre-reinforced polymer (CFRP) laminates. All beams had the same geometrical dimensions and internal steel reinforcement. The main parameters studied were the position and form of the CFRP laminates. Three of the beams were strengthened using different arrangements of CFRP plate reinforcement, and one was strengthened using CFRP sheets. The performance of the CFRP-strengthened beams was compared with that of an unstrengthened control beam. Peeling failure was the dominant mode of failure for all the strengthened beams tested. The beam strengthened with both top and bottom CFRP plates produced the highest load capacity. It was found that the longitudinal elastic shear stresses at the adhesive/concrete interface calculated at beam failure were close to the limiting value recommended in Concrete Society Technical Report 55.

No / Although several research studies have been conducted on simply supported concrete elements reinforced with fibre reinforced polymer (FRP) bars, there is little reported work on the behaviour of continuous elements. This paper reports the testing of four continuously supported concrete slabs reinforced with carbon fibre reinforced polymer (CFRP) bars. Different arrangements of CFRP reinforcement at mid-span and over the middle support were considered. Two simply supported concrete slabs reinforced with under and over CFRP reinforcement and a continuous concrete slab reinforced with steel bars were also tested for comparison purposes. All continuous CFRP reinforced concrete slabs exhibited a combined shear–flexure failure mode. It was also shown that increasing the bottom mid-span CFRP reinforcement of continuous slabs is more effective than the top over middle support CFRP reinforcement in improving the load capacity and reducing mid-span deflections. The ACI 440.1R–06 formulas overestimated the experimental moment at failure but better predicted the load capacity of continuous CFRP reinforced concrete slabs tested. The ACI 440.1R–06, ISIS–M03–07 and CSA S806-06 design code equations reasonably predicted the deflections of the CFRP continuously supported slabs having under reinforcement at the bottom layer but underestimated deflections of continuous slabs with over-reinforcement at the bottom layer.

There was developed a novel technological and constructive approach for the low-cost production of curved freeform formworks, which allow the production of single and double-curved fibre reinforced concrete. The scheduled approach was based on a flexible, asymmetrical multi-layered formwork system, which consists of glass-fibre reinforced plastic (GFRP). By using of the unusual anisotropic structural behavior, these GFRP formwork elements permitted a specific adjustment of defined curvature. The system design of the developed GFRP formwork was examined exhaustively. There were designed, numerically computed and produced prototypical curved freeform surfaces with different curvature radii. The fibre reinforced concrete had a compressive strength of 101.4 MPa and a 3-point bending tensile strength of 17.41 MPa. Beyond that, it was ensured that the TRC had a high durability, which has been shown by the capillary suction of de-icing solution and freeze thaw test with a total amount of scaled material of 874 g/m² and a relative dynamic E-Modulus of 100% after 28 freeze-thaw cycles.

There was developed a novel technological and constructive approach for the low-cost production of curved freeform formworks, which allow the production of single and double-curved fibre reinforced concrete. The scheduled approach was based on a flexible, asymmetrical multi-layered formwork system, which consists of glass-fibre reinforced plastic (GFRP). By using of the unusual anisotropic structural behavior, these GFRP formwork elements permitted a specific adjustment of defined curvature. The system design of the developed GFRP formwork was examined exhaustively. There were designed, numerically computed and produced prototypical curved freeform surfaces with different curvature radii. The fibre reinforced concrete had a compressive strength of 101.4 MPa and a 3-point bending tensile strength of 17.41 MPa. Beyond that, it was ensured that the TRC had a high durability, which has been shown by the capillary suction of de-icing solution and freeze thaw test with a total amount of scaled material of 874 g/m² and a relative dynamic E-Modulus of 100% after 28 freeze-thaw cycles.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Thermoplastic composites (TPCs) have shown significant advantages over thermosetting composites. They have only been put into use recently and global knowledge in TPCs is often proprietary, therefore a study into the application, processing and properties is of importance. The aim of the study is to contribute knowledge in TPCs for South African industry and academic institutions. This thesis studies continuous fibre reinforced thermoplastics (CFRTPs), focussing on the autoclave processing of commingled CFRTPs. A literature study provided background knowledge to CFRTPs regarding processing techniques and mechanics. Flexural testing and impact testing were performed on a variety of CFRTPs and thermosetting composites (TSCs). These tests were performed to further understand CFRTPs as well as to compare CFRTPs and TSCs. The flexural testing revealed that CFRTPs have comparable strength and stiffness to the TSCs that were tested. They also revealed that pre-consolidated sheets showed better and more consistent properties than sheets made from commingled fabric. The impact testing revealed that the tested CFRTPs and TSCs had similar impact resistance even though thermoplastic composites are supposed to be more impact resistant. The tests also showed that thick unreinforced thermoplastics had much higher impact resistance than the reinforced materials. Manufacturing experiments were performed to establish sound processing methods of CFRTPs. It was realised here that the high temperatures required to process the materials require specific processing consumables and tooling. The experiments began by processing flat panels in a convection oven with vacuum bagging techniques. They then progressed to autoclave processing of parts with complex geometry. An airline seat backrest was chosen as the case study in the application of CFRTPs. This application requires structural strength and stiffness and also has strict fire, smoke, toxicity and heat release (FSTH) requirements. Its geometry was sufficiently complex to demonstrate the use of commingled CFRTP material. Backrests were made from both CFRTPs and TSCs so that a comparison could be made between the two types. The backrest was modelled using finite element methods (FEM) to determine an adequate lay-up. This lay-up was then used for both the CFRTP and TSC backrests to ensure similarity between the backrests of both materials. LPET (modified polyethylene terephthalate) was the chosen thermoplastic matrix as it was more attainable than PPS (polyphenylene sulphide) CFRTPs. The backrests of both materials were manufactured in an autoclave with a vacuum bag method and then assembled using adhesives and bonding jigs. Testing revealed that the stiffness and mass of the CFRTP backrests were very similar to the epoxy backrests. This implies that commingled CFRTPs can replace the use of TSCs in similar applications. A basic cost comparison was also performed to compare the manufacture of CFRTP backrests to TSC backrests. Further work is needed to optimise processing time of these materials to make them more competitive with TSCs. The processing time of commingled materials will probably never be as quick as that of press formed pre-consolidated sheets. Their ability to be formed into more complex parts does however make their use advantageous. / AFRIKAANSE OPSOMMING: Termoplastiese saamgestelde materiale (Engels: thermoplastic composites (TPCs)) toon beduidende voordele bo termoverhardbare saamgestelde materiale. Hulle word eers sedert onlangs benut en algemene kennis in TPCs is dikwels patentregtelik, dus is ’n studie van die aanwending, prosessering en eienskappe daarvan van belang. Die doel van hierdie studie is om ’n bydrae te lewer tot die kennis van TPCs vir die Suid-Afrikaanse industrie en akademiese instellings. Hierdie tesis ondersoek kontinue veselversterkte termoplastieke (Engels: continuous fibre reinforced thermoplastics (CFRTPs)) en fokus op die outoklaafprosessering van vermengde (Engels: commingled) CFRTPs. ’n Literatuurstudie het die agtergrondkennis rakende die prosesseringstegnieke en meganika van CFRTPs verskaf. Buigtoetsing en impaktoetsing is op ’n verskeidenheid CFRTPs en termoverhardbare saamgestelde materiale (Engels: thermosetting composites (TSCs)) uitgevoer. Hierdie toetse is uitgevoer om CFRTPs beter te verstaan asook om CFRTPs en TSCs te vergelyk. Die buigtoetsing het onthul dat CFRTPs ooreenstemmende sterkte en styfheid het as die TSCs wat getoets is. Dit het ook getoon dat vooraf-gekonsolideerde plate beter en meer konsekwente eienskappe getoon het as plate wat van vermengde materiaal gemaak is. Die impaktoetsing het onthul dat die CFRTPs en TSCs wat getoets is soortgelyke impakweerstand gehad het, selfs al is termoplastiese saamgestelde materiale veronderstel om meer impakweerstand te toon. Die toetse het ook getoon dat dik onversterkte termoplastieke veel hoër impakweerstand gehad het as die versterkte materiale. Vervaardigingseksperimente is uitgevoer om betroubare prosesseringsmetodes vir CFRTPs vas te stel. Daar is besef dat die hoër temperature wat vereis word om die materiale te prosesseer ook spesifieke prosesseringsverbruiksware en -gereedskap benodig. Die eksperimente het begin met die prosessering van reguit panele in ’n konveksie-oond met vakuumsaktegnieke. Daar is toe aanbeweeg na die outoklaafprosessering van onderdele met komplekse geometrie. Die rugleuning van ’n vliegtuigsitplek is gekies as die gevallestudie in die gebruik van CFRTPs. Hierdie toepassing vereis strukturele sterkte en styfheid en is ook onderhewig aan streng vereistes t.o.v. brand, rook, toksisiteit en hittevrystellimg (Engels FSTH). Die geometrie daarvan was kompleks genoeg om die gebruik van vermengde CFRTP-materiaal te demonstreer. Rugleunings is gemaak van beide CFRTPs en TSCs sodat ’n vergelyking tussen die twee tipes gemaak kon word. Die rugleuning is gemodelleer deur eindige element metodes (EEM) te gebruik om ’n aanvaarbare oplegging te bepaal. Hierdie oplegging is toe gebruik vir beide die CFRTP en TSC rugleunings om die gelykvormigheid tussen die rugleunings van beide materiale te verseker. LPET (Engels: modified polyethylene terephthalate) was die gekose termoplastiese matriks aangesien dit meer verkrygbaar was as PPS (Engels: polyphenylene sulphide) CFRTPs. Die rugleunings van beide materiale is vervaardig in ’n outoklaaf met ’n vakuumsakmetode en toe geintegreer deur die gebruik van kleefstowwe en setmate. Toetsing het getoon dat die styfheid en massa van die CFRTP rugleunings baie soortgelyk was aan die epoksie rugleunings. Dit impliseer dat vermengde CFRTP die plek van TSCs in soortgelyke gebruike kan inneem. ’n Basiese kostevergelyking is ook gedoen om die vervaardiging van CFRTP-rugleunings teenoor TSC-rugleunings te vergelyk.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) in concrete is a well-known problem and usually occurs within the first few hours after the concrete has been cast. It is caused by a rapid loss of water from the concrete, either from the surface through evaporation or through absorption by dry subgrade or formwork in contact with the concrete and results in an overall reduction in concrete volume. If this volume reduction or shrinkage is restrained, plastic shrinkage cracks can occur. Plastic shrinkage cracks create an unsightly appearance on the concrete surface which reduces the quality of the concrete structure. These cracks also develop weak points in the concrete which can be widened and deepened later on by drying shrinkage and thermal movement. As a result harmful substances may enter the cracks causing accelerated concrete deterioration. These cracks may also expose the steel reinforcement causing it to corrode more aggressively. Consequently, the aesthetic value, serviceability, durability and overall performance of the concrete will be reduced. Therefore it is important to consider methods of limiting PSC. One of these methods is the addition of low volumes of polymeric fibres to concrete to reduce PSC. However, the application of this low volume fibre reinforced concrete (LV-FRC) is not clearly understood since there is a lack of knowledge and guidance available for the use of LV-FRC. The objective of this study is to gain a full understanding of PSC behaviour in conventional concrete and LV-FRC by investigating the effects of evaporation and bleeding as well as the effect of various fibre properties on PSC. The following significant findings were attained: A basis for a crack prediction model in conventional concrete was developed using the average differences in cumulative evaporation and cumulative bleeding to create a crack prediction value (CPV). This preliminary model showed that there exists a certain CPV range (-0.2 to 0.4 kg/m2 for this study) where a slight decrease in the CPV results in a significant PSC reduction. It also showed that if the CPV falls outside this range, varying the bleeding or evaporation conditions will have very little effect on the PSC. A study on the fibre properties in LV-FRC showed that there exist certain limits to the fibre volume, length and diameter where a further increase or decrease in value will have no or little effect on reducing PSC. It also showed that the effect of the fibres depend on the level of severity of PSC. The knowledge gained from this investigation can serve as a basis for the design of a model that can predict the risk of PSC in conventional concrete and specify preventative measures needed to reduce this risk. It also provides information that can be used to develop guidelines for the effective use of LV-FRC. / AFRIKAANSE OPSOMMING: Plastiese krimp krake (PKK) in beton is `n bekende probleem en vorm gewoonlik binne die eerste paar uur nadat die beton gegiet is. Dit word veroorsaak deur die vinnige waterverlies vanuit die beton, óf deur verdamping vanaf die beton oppervalk óf deur absorpsie van `n droeë grondlaag of bekisting wat in kontak is met die beton. Dit veroorsaak `n algehele vermindering in beton volume. As hierdie krimping van die beton beperk word, kan plastiese krimp krake ontstaan. PKK skep 'n onooglike voorkoms van die beton oppervlakte en verlaag die kwaliteit van die beton struktuur. Hierdie krake tree ook op as swak plekke in die beton wat later kan verbreed of verdiep deur droogkrimping en termiese beweging. Gevolglik kan skadelike stowwe vanuit die omgewing die krake binnedring wat lei tot versnelde agteruitgang van die beton. Hierdie krake kan ook die staalbewapening ontbloot wat veroorsaak dat dit vinniger roes. Gevolglik verminder die estetiese waarde, diensbaarheid, duursaamheid en algehele prestasie van die beton. Daarom is dit belangrik om metodes te ondersoek vir die beperking van PKK. Een van hierdie metodes is die byvoeging van lae volumes polimeer vesels tot beton om PKK te verminder. Die toepassing van hierdie lae volume - vesel versterkte beton (LV-VVB) word egter nog nie volledig verstaan nie as gevolg van 'n algemene gebrek aan kennis en riglyne vir die gebruik van die LV-VVB. Die doel van hierdie studie is om 'n volledige begrip van PKK gedrag in normale beton asook LV-VVB te kry. Dit word behaal deur die effek van verdamping en bloei op PKK sowel as die effek van verskillende vesel eienskappe op PKK te ondersoek. Die volgende noemenswaardige bevindinge is bekry. • Die basis van 'n kraak voorspellingsmodel vir gewone beton is ontwikkel deur gebruik te maak van die gemiddelde verskil tussen die kumulatiewe verdamping en die kumulatiewe bloei om 'n kraak voorspellingswaarde (KVW) te vorm. Hierdie voorlopige model toon dat daar `n sekere KVW interval ontstaan (-0,2 tot 0,4 kg/m2 vir hierdie studie) waar slegs 'n effense vermindering in die KVW 'n geweldige vermindering in die PKK tot gevolg het. Dit dui ook aan dat, indien die KVW buite hierdie interval val, ʼn verandering in die bloei of verdamping toestande `n baie klein invloed op die PKK het. 'n Studie oor die vesel eienskappe in LV-VVB het gewys dat daar sekere grense is aan die vesel volume, lengte en deursnee waardes, waar 'n verdere toename of afname in waarde min of geen effek het op die vermindering van PKK nie. Dit wys ook dat die effek van die vesels grotendeels afhanklik is van die risiko vlak vir PKK. Die kennis wat uit hierdie ondersoek opgedoen is, kan dien as 'n basis vir die ontwerp van 'n model wat die risiko van PKK in gewone beton kan voorspel en daarvolgens besluit op 'n voorkomingsmaatsreël om hierdie risiko te verminder. Dit bied ook inligting wat gebruik kan word om riglyne te ontwikkel vir die effektiewe gebruik van LV-VVB.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This study set out to determine the debonding of externally applied Carbon Fibre Reinforced Polymer (CFRP) plates from RC structures under cyclic loading. Triplet shear tests and finite element (FE) analyses were done on the epoxy to determine the bond stress between the CFRP plate and a reinforced concrete specimen. From these tests and analyses the average shear strength of the bond between the epoxy and concrete substrate was determined and the shear strength of the epoxy specified by the supplier could be confirmed. A case study of a statically loaded beam was performed to verify the bond strength. Finally a reinforced concrete (RC) T-section was designed and pre-cracked to simulate a damaged beam in practice. These sections were then externally reinforced by bonding CFRP plates onto the face of the web. The sections were subjected to static and cyclic loading at different force amplitudes. Along with the experimental tests, FE models were developed and analysed which had the same geometrical and material properties as the experimental specimens. Due to time constraint a FE mesh objectivity study was not done, but the chosen element size is believed to be sufficiently small to replicate the experimental tests objectively. The FE analyses and the experimental tests yielded results that were close to each other on both the global scale and in terms of localised behaviour, thus it was decided that the computational approach could be used for the final design of a model of the debonding of CFRP plates bonded onto RC beams under cyclic loading because the data can be analysed more easily and a large variation of tests can be done. For the T-section 3 tests were conducted; a pull-off (static) test where the bonded CFRP plate was pulled from a specimen to get the ultimate failure envelope of the test specimens. The static test was followed by cyclic tests with force amplitude of 85% and 65% of the ultimate pull-off strength. Different measurements were taken to get the global and local displacement behaviour of the section. The global displacement was measured by means of a linear variable displacement transducer (LVDT, displacement meter) clamped onto the CFRP plate that pushed on the top of the concrete and the local displacement was measured with the help of the Aramis system. The displacement was then compared to the same displacements of nodes and elements in the FE models. The result was a confirmation that the results from the FE models were sufficient to design a model for cyclic debonding of CFRP plates from RC structures. From the FE models the relative displacement between the CFRP plate and concrete was obtained in the vicinity of a crack. This relative displacement was then normalised by the respective stress range of the different tests, from which the normalised relative displacement was plotted against the number of cycles to get an equation limiting the number of cycles for a specific stress range. From the results, it appears that for cyclic load levels up to 65% of the peak static resistance, a threshold number of load cycles are required for delamination initiation. Subsequently, a near constant delamination rate is reached. The delamination rate is significantly lower for lower cyclic load levels. Finally, an unstable delamination stage is reached at a level of about 65 μm for all the analyses, after which CFRP pull-off is imminent. Service life design of CFRP reinforcement of RC beams should take into consideration the delamination initiation threshold, the subsequent delamination rate and finally the initiation of unstable delamination. / AFRIKAANSE OPSOMMING: Die projek is uitgevoer om die delaminasie van ekstern aangewende Koolstof Vesel Versterkte Polimeer (KVVP) stroke op gewapende beton strukture te bepaal onder sikliese belasting. Triplet skuif toetse is gedoen op die gebruikte epoksie om die verband-sterkte te bepaaltussen die KVVP stroke en die beton proefstuk. Die skuif toetse is ook met behulp van die eindige element (EE) metode geanaliseer. Die resultaat van die toetse en analises het gewys dat die verband sterkte tussen die KVVP stroke en beton gelyk is aan die skuif sterkte van die epoksie wat verskaf is. `n Gevalle studie van `n monotonies belaste balk is gedoen om die verband-sterkte te verifieër. `n Gewapende beton T-snit is ontwerp en voor-af gekraak om `n beskadigde balk in die praktyk voor te stel. Die beskadigde proefstukke is vervolgens ekstern versterk met KVVP stroke wat aan die web van die T-snit vas geplak is. Die versterkte T-snitte is getoets onder statiese en sikliese belasting. Die sikliese toetse is ook onder verskillende spanningsamplitudes getoets. Om die eksperimentele toetse te verifieër is EE modelle gebou en geanaliseer wat dieselfde geometriese en materiaal eienskappe as die eksperimentele proefstukke gehad het, maar as gevolg van `n tydsbeperking is `n sensitiwiteit studie oor die element grootte nie gedoen nie. Die element grootte is klein genoeg gekies en word beskou as voldoende om die gedrag objektief te simuleer. Die EE analises en eksperimentele resultate was na genoeg aan mekaar op beide globale en lokale vlak. Dus is `n analitiese benadering tot die toetse vervolgens gebruik vir die ontwerp van `n model vir delaminasie van KVVP stroke van gewapende beton strukture onder sikliese belasting. Die EE metode stel die analis in staat om `n verskeidenheid van toetse relatief vinnig uit te voer en om die data van die toetse vinniger te interpreteer as deur fisiese eksperimentele toetse. Drie eksperimente is uitgevoer op die T-snitte, `n aftrek-toets (staties) waar die KVVP strook van `n proefstuk afgetrek is om die falingsomhullende diagram te kry en dan ook twee sikliese toetse teen 85% en 65% van die krag amplitude van die falingskrag. Verplasingsmeters is gebruik om die globale verplasing te kry, deur dit vas te klamp op die KVVP strook en dan die verplasing te meet relatief tot die bokant van die beton. Die lokale veplasing is met behulp van die Aramis sisteem verkry. Die eksperimentele verplasings is dan vergelyk met verplasings van die ooreenstemmende nodes en elemente in die EE modelle. Deur die vergelyking van die resultate is dit bevestig dat die eindige element modelle voldoende is om die model vir sikliese delaminasie van KVVP stroke van gewapende beton strukture te gebruik vir die ontwerp. Uit die EE modelle is die relatiewe verplasing tussen die KVVP strook en die beton gekry in die omgewing van `n kraak. Die relatiewe verplasing is genormaliseer deur elkeen se spanningsamplitude. Die genormaliseerde relatiewe verplasing is dan teenoor die aantal siklusse geteken waarvan `n vergelyking vir die maksimum verplasing afgelei is om die aantal siklusse vir `n gegewe spanning amplitude te beperk. Uit die resultate blyk dit dat vir sikliese laste tot en met 65% van die piek statiese weerstand `n aantal siklusse moontlik is voordat delaminasie begin waarna `n konstante delaminasie tempo bereik word. Die delaminasie tempo is stadiger vir sikliese laste teen `n laer belastings amplitude. Laastens word `n onstabiele delaminasie fase bereik by `n vlak van ongeveer 65 μm, na die oorgang delamineer die KVVP strook binne enkele siklusse. Die beginpunt van delaminasie, die delaminasie tempo en laastens die begin van onstabiele delaminasie moet in gedagte gehou word by die ontwerp diens leeftyd van KVVP versterkte gewapende beton balke.

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, 2013. / ENGLISH ABSTRACT: Macro synthetic fibre reinforced concrete (SynFRC) is a relatively new concrete for the purpose of being used in structural elements which only require minimum reinforcement and are supported continuously by sub-layers. One structural element that is of particular interest is slabs-on-grade which is supported by a subgrade/sub-base and requires minimum reinforcement to control the shrinkage strains which may result in cracking. The aim of this project is to investigate the potential use of macro SynFRC in the application of controlling drying shrinkage cracking (DSC) in concrete slabs-on-grade. The focus is on the use of concrete slabs-on-grade that is intended for industrial floors. The SynFRC material parameters of interest were characterised first with the aid of various experimental tests. These are: flexural tests, compression tests, friction tests between the SynFRC and wooden surfaces used for full scale testing, and the shrinkage of the concrete. Next the post-cracking tensile behaviour of the SynFRC was determined by way of an inverse analysis. These tensile responses were subsequently used to perform a series of different finite element analyses. These analyses were performed on specific slabs-on-grade to determine the effects of the added tensile behaviour of the SynFRC on the DSC. The results obtained concerned: the spacing of cracks, the maximum and average crack width, and the difference in crack width between the normal concrete (NC) and the SynFRC. These changes take place in accordance to the concrete age. From the analyses it was determined that the addition of fibres gives the concrete a ductility that allows the concrete to crack more than NC, yet does not allow the cracks to propagate. This applies to low fibre contents of less than 0.4% by volume and a slab thickness of 200mm, as well as to fibre contents that have Re,3 values of 0.51 and higher. Moreover, it results in improvements seen when adding fibres if the friction is sticky, meaning when the maximum friction between the slab and the subgrade is reached with a very small amount of movement. With a stickier friction though smaller crack widths occur within both the NC and the SynFRC. / AFRIKAANSE OPSOMMING: Makro sintetiese vesel versterkte beton (SynFRC) is 'n relatiewe nuwe beton. Dit het ten doel om gebruik te word in strukturele elemente wat minimale versterking benodig en wat deurlopend deur sublae ondersteun word. Een spesifieke strukturele element van belang is grondvloere wat deur 'n sublaag ondersteun word en wat minimale ondersteuning benodig om die krimping vervorming te beheer wat moontlike krake kan veroorsaak. Die doel van die projek was om die potensiële gebruik van makro sintetiese vesels te ondersoek tydens die beheer van die uitdroog krimp kraking van 'n beton grondvloer. Die fokus was op die gebruik van betonvloere vir fabrieksdoeleindes. Die eienskappe van SynFRC materiale is vooraf vasgestel vir die doel van verskeie eksperimentele toetse. Hierdie toetse sluit in buigbaarheidstoetse, druktoetse, krimping van beton en toets van wrywing tussen die SynFRC en hout oppervlaktes wat gebruik is vir volskaalse toets. Die trek gedrag van SynFRC na kraking is vasgestel deur inverse analise. Hierdie trek gedrag is dan gebruik om 'n reeks eindige element analises uit te voer. Hierdie analises is uitgevoer op spesifieke grondvloere om die effek te bepaal van verhoogde trek gedrag van SynFRC op die uitdroog krimp kraking. Volgens die uitslae sodoende verkry was die kraakspasiëring, die maksimum en gemiddelde kraakwydte en die verskil in die kraakwydte tussen normale beton en die SynFRC as ‘n funksie van beton oudedom. Vanuit die analises het dit duidelik geblyk dat die byvoeging van vesels die beton se smeebaarheid verhoog het en dit het tot gevolg gehad dat die beton meer krake vorm, maar dat die krake nie vergroot nie. Dit is waargeneem by 'n lae vesel inhoud van minder as 0.4% per volume en 'n betonblad met 'n dikte van 200mm. Dit is ook waargeneem by 'n hoër vesel volume wat Re,3 waardes van 0.51 en hoër het. Kleiner kraakwydte is waargeneem waar vesel volume verhoog is indien die wrywing hoër is, bedoelende dat die maksimum wrywing tussen die betonblad en die sublaag bereik is met baie min beweging. Daar het wel kleiner kraakwydtes in beide die normale beton en die SynFRC voorgekom waar daar hoër wrywing was.