Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: There is an increasing demand for the development and use of innovative materials with
reduced cost of construction while offering improved structural properties. Steel fibre
reinforced concrete (SFRC) can be used as a structural material to substitute the conventional
reinforcing bars partially or fully. However, there is little or no codified approach on the
design procedures for SFRC members in the latest guidelines outlined in the draft 2010
Model code.
It is against this background that analytical methods are derived in this study for the
determination of the flexural capacity of strain-softening, deflection-hardening SFRC with
and without steel reinforcing bars. Models used for the determination of the flexural capacity
of SFRC rectangular sections are based on equivalent stress blocks for both compression and
tensile stresses. These are derived from an elastic-perfect plastic model for compression and
either an elastic-constant post-peak response or Rilem’s multi-linear model for tension, in
which strain compatibility and force equilibrium theories are used. By employing the
equivalent stress blocks for both tensile and compressive stress states, parameters are defined
by converting the actual stress-strain distribution to an equivalent stress block, depending on
the ratio of yield (or cracking) strain and post-yield (post-cracking) strains. Due to the
simplicity of a drop-down tensile model and a bilinear compression model, these material
models are used for the subsequent derivation of the flexural models for both SFRC with and
without steel reinforcing bars.
An experimental program is designed and executed for model verification. This includes
material characterisation experiments for the determination of material model input
parameters, and main beam flexural experiments for the determination of the beam bending
capacity. An indirect tensile test is used for the characterisation of the tensile behaviour while
a four-point bending test is used for beam bending behaviour.
Both flexural models for SFRC with and without reinforcing bars have been verified to fairly
predict the flexural capacity of the beams. However, the flexural model for SFRC with steel
bars offers some challenges as to whether the synergetic effect of using both steel bars and
steel fibres should be incorporated at the low fibre volumes as used in the verification
exercise. Furthermore, the use of indirect methods to characterise tensile behaviour added
some uncertainties in the material model parameters and hence may have affected the
predictability of the model. More research on the verification of the models is required to
enable the use of a wider concrete strength spectrum for the verification and possible
modification of the models. Studies on the model uncertainty may also help determine the
reliable safety factor for the use of the model in predicting design strength of beam sections at
a prescribed reliability index. / AFRIKAANSE OPSOMMING: Daar is ‘n groeiende aanvraag na die ontwikkeling en gebruik van innoverende materiale met
verminderde konstruksiekoste maar verbeterde strukturele eienskappe. Staalvesel-gewapende
beton (SVGB) kan gebruik word as strukturele materiaal om die konvensionele
wapeningstawe gedeeltelik of ten volle te vervang. Daar is egter min of geen gekodifiseerde
benaderings tot die ontwerpprosedures vir SVGB-dele in die nuutste riglyne uitgestippel in
die konsepweergawe van die 2010 Modelkode nie.
Dit is teen hierdie agtergrond dat in hierdie studie analitiese metodes afgelei is vir die
bepaling van die buigkapasiteit van spanning-versagtende, defleksie-verhardende SVGB met
en sonder staalbewapeningstawe. Modelle wat gebruik is vir die bepaling van die
buigkapasiteit van SVGB reghoekige snitte is gebaseer op ekwivalente spanningsblokke vir
beide druk- en trekspannings. Hierdie is afgelei van ‘n elasties-perfekte plastiese model vir
druk en óf ‘n elasties-konstante post-piek respons óf Rilem se multi-lineêre model vir
spanning, waarin teorieë vir drukkapasiteit en krag-ewewig gebruik is. Deur die ekwivalente
spanningsblokke vir beide trek- en drukspanningstoestande te implementeer, is parameters
bepaal deur die werklike verspreiding van spanningsdruk om te wissel na ‘n ekwivalente
spanningsblok, afhangend van die verhouding van swig- (of kraak-)spanning en post-swig
(post-kraak) spannings. Te wyte aan die eenvoud van ‘n aftrek trekmodel en ‘n bilineêre
kompressiemodel, is hierdie materiaalmodelle gebruik vir die daaropvolgende afleiding van
die buigingsmodelle vir beide SVGB met en sonder staalbewapeningstawe. ‘n Eksperimentele program vir modelkontrolering is ontwerp en uitgevoer. Dit sluit eksperimente in vir materiaalbeskrywing, om invoerparameters van materiaalmodelle te
bepaal, asook eksperimente vir hoofbalkbuigings, om balkbuigingskapasiteit te bepaal. ‘n
Indirekte trektoets is gebruik vir die beskrywing van die trekgedrag, terwyl ‘n vierpuntbuigingstoets
gebruik is vir balkbuiggedrag.
Dit is bewys dat beide buigingsmodelle vir SVGB met en sonder staalbewapeningstawe die
buigingskapasiteit van die balke redelik akkuraat kan voorspel. Nietemin, bied die
buigingsmodel vir SVGB met staalbewapeningstawe sekere uitdagings: die vraag ontstaan
rondom die insluiting van die sinergetiese effek van die gebruik van beide staalstawe en
staalvesels met die lae veselvolumes soos gebruik in die kontroleringsoefening. Verder het
die gebruik van indirekte metodes om die buigingsgedrag te bepaal, onsekerhede gevoeg by
die materiaalmodelparameters en dit mag dus as sulks die voorspelbaarheid van die model
beïnvloed. Meer navorsing moet uitgevoer word oor die kontrolering van die modelle sodat
‘n wyer spektrum van betonsterkte gebruik kan word vir die verifikasie en moontlike
aanpassing van die modelle. Navorsing oor die wisselvalligheid van die modelle mag ook
help om die betroubare veiligheidsfaktor te bepaal vir die model se gebruik in die berekening
van ontwerpkrag van balkdele teen ‘n voorgeskrewe betroubaarheidsindeks.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/18088 |
| Date | 12 1900 |
| Creators | Mbewe, Peter Binali Kamowa |
| Contributors | Van Zijl, G. P. A. G., 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 | 148 p. : ill. |
| Rights | Stellenbosch University |
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