Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Fibre reinforced concrete (FRC) transforms concrete from a characteristically brittle material to one with a post-crack tensile residual capacity. Its application in industry has varied over the past of which the tensile properties have generally been used in the form of crack mitigation. More recently, the introduction of steel fibres has broadened this scope to structural applications in which the resisting tensile stresses that develop within a steel FRC (SFRC) element can be rather significant. This thesis reviews the existing practices and design models associated with SFRC and the suitability of its implementation as the sole form of reinforcement in in-situ cast flat slab systems. As a material SFRC is dependent on a number of factors which include the fibre type and volume, fibre distributions, element size, as well as the support and applied load conditions. Thus, its performance can be considered rather variable in comparison to conventional concrete should the incorrect practices be implemented. In order to adequately define the material characteristics, it is necessary to use test procedures that accurately reflect on the intended structural application. As a result a number of test procedures have been developed. In addition to this, the post-crack material performance is associated with a non-linear behaviour. This attribute makes the design of structural SFRC elements rather difficult. In an attempt to simplify this, existing design models define stress-strain or stress-crack width relations in which assumptions are made regarding the cross-sectional stress distribution at specified load states. This thesis takes on two parts in defining the suitability of SFRC as the sole form of reinforcement in flat slab systems. The first is a theoretical investigation regarding the micro and macro scale material performance of SFRC, the practices that exist in defining the material properties and its application in structural systems (particularly suspended slab systems), and a breakdown of the existing design models applicable to strain softening deflection hardening SFRC materials. The second part is an experimental program in which the fresh state and hardened state material properties of specified SFRC mix designs defined
through flow and beam testing respectively. These properties are then implemented in the
design and construction of full scale flexural and punching shear test slabs in an attempt to
verify the theory applied.
The investigation reveals that the use of SFRC significantly improves the ductility of
concrete systems in the post-crack state through fibre crack bridging. This ductility can result
in deflection hardening of flat slab systems in which the redistribution of stresses increases
the load carrying capacity once cracking has taken place. However, the performance of large
scale test specimens is significantly influenced by the construction practices implemented in
which the material variability increases as a result of non-uniform fibre distributions. The
results indicate that the load prediction models applied have potential to adequately predict
the ultimate failure loads of SFRC flat slab systems but however cannot account for possible
non-uniform fibre distributions which could result in premature failure of the system. / AFRIKAANSE OPSOMMING: Vesel versterkte beton (VVB) verander beton van die kenmerkende uiters bros material na ‘n material met ‘n residuele post-kraak trekkapasiteit. Die toepassing daarvan in die bedryf het
in die verlede gewissel en die trek eienskappe is oor die algemeen gebruik vir kraak
vermindering. Meer onlangs het die bekenstelling van staal vesel hierdie omvang verbreed
na die strukturele toepassings waar trekspannings wat ‘n VVB element kan weerstaan
noemenswaardig kan wees. Hierdie tesis ondersoek bestaande praktyke en ontwerpmodelle
met die oog op staalvesel versterkte beton (SVVB) en die geskiktheid van die
implementering daarvan as die enigste vorm van bekisting in in-situ gegiete plat blad stelsels.
As ‘n materiaal, is SVVB afhanklik van ‘n aantal faktore wat die tipe vesel en volume, vesel
verspreiding, element grootte, sowel as die randvoorwaardes tipe aangewende las insluit. As
gevolg hiervan, kan die gedrag van SVVB, wat korrek geïmplimenteer word, as redelik
varieerbaar beskou word wanneer dit met konvensionele beton vergelyk word. Ten einde die
materiaaleienskappe voldoende te definieer, is dit noodsaaklik dat prosedures wat die
strukturele toepassing akuraat voorstel, getoets word en daarom is ‘n aantal toets prosedures
ontwikkel. Verder het die post-kraak materiaalgedrag ‘n nie-lineêre verband wat
struktuurontwerp met SVVB redelik moeilik maak. Om dit te vereenvoudig, definieer
bestaande ontwerpmodelle spanning-vervorming of spanning-kraakwydte verhoudings
waarin aannames gemaak word ten opsigte van die spanningsverdeling oor ‘n snit, gegewe
sekere lastoestande.
Hierdie studie bestaan uit twee dele wat die geskiktheid van SVVB as die enigste vorm van
bikisting in plat blad stelsels definieer. Die eerste deel bestaan uit ‘n teoretiese ondersoek
wat handel oor die mikro- en makro-skaal materiaalgedrag van SVVB, die praktyke wat
bestaan om die materiaaleienskappe en toepassing in strukturele sisteme (spesifiek opgelegde
blad stelsels) te definieer, en ‘n uiteensetting van die bestaande ontwerpmodelle wat van toepassing is vir defleksie as gevolg van vervormingsversagting wat SVVB material verhard.
Die tweede deel bestaan uit ‘n eksperimentele program waarin die materiaaleienskappe van
gespesifiseerde SVVB meng-ontwerpe in die vars toestand en in die verharde toestand
gedefinieer word deur middel van vloei- en balktoetse onderskeidelik. Hierdie eienskappe
word dan toegepas vir die ontwerp en konstruksie van volskaalse buig- en ponsskuif
toetsblaaie ten einde die modelle en teorie wat toegepas is, te bevestig.
Die ondersoek toon dat die gebruik van SVVB die duktiliteit van beton sisteme
noemenswaardig verbeter in die post-kraak toestand deur kraak oorbrugging. Hierdie
duktiliteit kan defleksie verharding van plat blad stelsels veroorsaak waarin die herverdeling
van spannings, nadat kraking plaasgevind het, die lasdraende kapasiteit verhoog. Die gedrag
van die grootskaalse toetsmonsters word egter noemenswaardig beïnvloed deur die
konstruksiemetodes wat geïmplementeer word waarin die materialveranderlikheid toeneem as
‘n gevolg van nie-uniforme vesel verdelings. Die resultate dui daarop dat die modelle wat
toegepas is om die laste te voorspel, die potensiaal het om die grens falingslas van SVVB plat
blad stelsel voldoende te voorspel, maar neem nie moontlike nie-uniforme veselverdelings
wat kan lei tot vroeë faling van die stelsel in ag nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17861 |
| Date | 12 1900 |
| Creators | Jarrat, Robert |
| 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 | English |
| Type | Thesis |
| Format | 185 p. : ill. |
| Rights | Stellenbosch University |
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