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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20355 |
| Date | 03 1900 |
| Creators | Mouton, Christiaan Johannes |
| Contributors | Boshoff, W. P., Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 170 p. : ill. |
| Rights | Stellenbosch University |
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