Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Tunneling in busy urban areas is becoming a common practice, caused by the everincreasing number of commuters. This causes a decline in the service level that the surface transportation systems provide in cities. Tunneling induces movement of the soil directly surrounding the tunnel. These movements are translated into surface movements, which are translated into structural displacements of the surrounding surface infrastructure. These displacements, for which the infrastructure may not have been designed, put a question mark on the infrastructure aesthetics, serviceability, as well as structural stability. Burland and Wroth (1974) proposed a simple analytical damage assessment approach (Limiting tensile strain method (LTS)) to aid in the design of tunnels with respect to the structural integrity of the affected surface infrastructure. This study is concerned with the accuracy of this approach applied to the damage assessment of laterally unconfined, solid masonry walls, subject to a sagging mode of settlement deformation with no soil to wall friction. It is also concerned with the proposal of modifications to the approach, where deemed necessary. Finite element models of solid masonry walls are built and analysed in order to determine the accuracy of the simple analytical damage assessment approach with regard to the prediction of strains in solid masonry walls subject to tunneling-induced displacements. The predictions are found to be accurate for walls ofL/H ratio equal to 2 and larger. For walls of L/H ratio smaller than 2, the predictions are found to be underestimates. The simple analytical damage assessment approach is unable to account for the stiffness of the soil directly under the foundation of the wall. The stiffness of the soil plays a major role in the stress and strain distributions in the wall. It is therefore deemed necessary to modify the simple analytical damage assessment approach by accounting for the soil to wall interaction and the effect it has on the settlement damage to solid masonry walls. The soil to wall interaction is found to reduce the number of mitigating measures originally recommended for the walls, by the simple analytical damage assessment approach, as it accounts for the bedding of the wall into the soil previously unaccounted for. This study has reached the point where it is able to accurately predict whether a laterally unconfined, solid masonry wall, subject to a sagging mode of settlement deformation with no soil to wall friction will experience magnitudes of strain surpassing the yielding strain of the material. This was fundamentally achieved by developing a better representation of the strains in solid masonry walls as well as accounting for the inherent soil to wall interaction This study is intended to pioneer the proliferation of similar studies for various other structures. A methodology, applicable for similar investigations envisaged for other structures, is hereby developed. / AFRIKAANSE OPSOMMING: Tonnels in besige stedelike gebiede is besig om 'n allerdaagse verskynsel te raak a.g.v. die skerp toename in pendelaars. Die rede hiervoor is die afname in die kwaliteit van bogrondse vervoerdienste. Tonnels veroorsaak beweging van grond direk in aanraking met die tonnel. Hierdie bewegings versprei na die oppervlak wat strukturele verplasings veroorsaak. Vir n' struktuur wat nie vir hierdie verplasings ontwerp is nie, ontstaan vrae oor die estetika, diensbaarheid asook die stabiliteit van die struktuur. Burland en Wroth (1974) het 'n eenvoudige analitiese skade-assesseringsmetode voorgestel (Limiting tensile strain method (LTS)) vir die ontwerp van tonnels m.b.t. die strukturele integriteit van die geaffekteerde oppervlak se infrastruktuur. Hierdie studie handeloor die akkuraatheid van dié benadering, toegepas op die assessering van skade op lateraalonbeperkte, soliede messelwerkmure, onderhewig aan die deurbuigings mode van versakkingsdeformasie, met geen grond tot muur wrywing. Eindige element modelle van messelwerkmure is gebou en geanaliseer om die akkuraatheid van die eenvoudige analitiese skade-assesseringsmetode te bepaal, m.b.t. die voorspelling van die vervormings in messelwerkmure onderhewig aan grondverplasings veroorsaak deur tonnels. Die voorspellings is akkuraat in mure met lengte tot hoogte (L/H) verhoudings van 2 en hoër. Vir mure met LIH verhoudings van minder as 2, word daar gevind dat die voorspellings onkonserwatief is. By die eenvoudige analitiese skade-assesseringsmetode word die styfheid van grond direk onder die fondasies van die muur nie in ag geneem nie. Die grondstyfheid speel 'n kardinale rol by die spannings- en vervormingsverdelings in die muur. Dit is daarvoor nodig om die eenvoudige analitiese skade-assesseringsmetode aan te pas om die grond tot muur interaksie in ag te neem. Die interaksie tussen die grond en die muur veroorsaak 'dat a minder of geen skade voorkomende maatreëls getref hoef te word as wat oorspronklik deur die envoudige analitiese skade-assesseringsmetode voorgestel sou word. Dit neem die inbedding van die muur in die grond in ag, wat voorheen geïgnoreer is. Die studie het 'n punt bereik waar dit akkuraat kan voorspelof 'n lateraalonbeperkte, soliede messelwerkmuur, onderhewig aan die deurbuiging mode van versakkingsdeformasie en met geen grond tot muur wrywing, vervormings hoër as die swigvervorming van die material salondervind. Dit is bereik deur 'n beter voorstelling van die vervormings in soliede messelwerkmure asook die in agneming van inhirente grond tot muur interaksie. Die studie is veronderstel om die voorganger te wees vir soortgelyke studies toegepas op verskeie ander struktuurklasse. Die sistematiese metode wat hier ontwikkel is kan toegepas word op die ander struktuurklasse.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) is the cracking caused by the early age shrinkage of concrete within the first few hours after the concrete has been cast. It results in unsightly surface cracks that serve as pathways whereby corroding agents can penetrate the concrete which shortens the expected service life of a structure. PSC is primarily a problem at large exposed concrete surfaces for example bridge decks and slabs placed in environmental conditions with high evaporation rates. Most precautionary measures for PSC are externally applied and aimed to reduce the water loss through evaporation. The addition of a low dosage of polymeric fibres to conventional concrete is an internal preventative measure which has been shown to reduce PSC. The mechanisms involved with PSC in conventional and low volume fibre reinforced concrete (LV-FRC) are however not clearly understood. This lack of knowledge and guidance leads to neglect and ineffective use of preventative measures. The objective of this study is to provide the fundamental understanding of the phenomena of PSC. To achieve the objective, an in depth background study and experiments were conducted on fresh conventional concrete and LV-FRC. The three essential mechanisms required for PSC are: 1→ Capillary pressure build-up between the particles of the concrete is the source of shrinkage. 2→ Air entry into a concrete initiates cracking. 3→ Restraint of the concrete is required for crack forming. The experiments showed the following significant findings for conventional and LV-FRC: PSC is only possible once all the bleeding water at the surface has evaporated and once air entry has occurred. The critical period where the majority of the PSC occurs is between the initial and final set of concrete. Any preventative measure for PSC is most effective during this period. The bleeding characteristics of a mix have a significant influence on PSC. Adding a low volume of polymeric fibres to concrete reduces PSC due to the added resistance that fibres give to crack widening, which increases significantly from the start of the critical period. The fundamental knowledge gained from this study can be utilized to develop a practical model for the design and prevention of PSC in conventional concrete and LV-FRC. / AFRIKAANSE OPSOMMING: Plastiese krimp krake (PSK) is die krake wat gevorm word a.g.v. die vroeë krimping van beton binne die eerste paar ure nadat die beton gegiet is. Dit veroorsaak onooglike oppervlak krake wat dien as kanale waardeur korrosie agente die beton kan binnedring om so die dienstydperk van die struktuur te verkort. Dit is hoofsaaklik ʼn probleem by groot blootgestelde beton oppervlaktes soos brug dekke en blaaie wat gegiet is in klimaat kondisies met hoë verdamping tempo’s. Meeste voorsorgmaatreëls vir PSK word ekstern aangewend en beperk die water verlies as gevolg van verdamping. Die byvoeging van ʼn lae volume polimeriese vesels is ʼn interne voorsorgmaatreël wat bekend is om PSK te verminder. Die meganismes betrokke ten opsigte van PSK in gewone beton en lae volume vesel versterkte beton (LV-VVB) is vaag. Die vaagheid en tekort aan riglyne lei tot nalatigheid en oneffektiewe aanwending van voorsorgmaatreëls. Die doel van die studie is om die fundamentele kennis oor die fenomeen van PSK te gee. Om die doel te bereik is ʼn indiepte agtergrond studie en eksperimente uitgevoer op gewone beton en LV-VVB. Die drie meganismes benodig vir PSK is: 1→ Kapillêre druk tussen die deeltjies van die beton is die hoof bron van krimping. 2→ Lugindringing in die beton wat krake inisieer. 3→ Inklemming van die beton is noodsaaklik vir kraakvorming. Die eksperimente het die volgende noemenswaardige bevindinge opgelewer: PSK is slegs moontlik indien al die bloeiwater van die beton oppervlakte verdamp het en indien lug die beton ingedring het. Die kritiese periode waar die meerderheid van die PSK plaasvind is tussen die aanvanklike en finale set van die beton. Enige voorsorgmaatreël vir PSK is mees effektief gedurende die periode. Die bloei eienskappe van ʼn meng het ʼn noemenswaardige effek op die PSK. Die byvoeging van ʼn lae volume polimeriese vesels tot beton verminder die PSK deur die addisionele weerstand wat die vesels bied teen die toename in kraakwydte. Die weerstand vergroot noemenswaardig vanaf die begin van die kritiese periode. Die fundamentele kennis wat in die studie opgedoen is, kan gebruik word vir die ontwikkeling van ʼn praktiese model vir die ontwerp en verhoed van PSK in gewone beton en LV-VVB.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Constructability issues cause dire repercussions in the industry and often pose as overwhelming threats to the successful delivery of projects. Constructability issues mainly arise from a design, which does not sufficiently embody the knowledge and expertise of the construction phase. Subsequently this creates a variety of negative secondary effects during project execution, which eventually manifest as time-, budget- and quality-risks to the project. The research thesis explores the status quo of constructability issues in South Africa, with specific reference to the relationship between construction and design. It is well known that close collaboration between consultants and contractors has the potential to lead to more effective construction processes, improved construction safety and to cost effective structural solutions. Not all contract forms allow sufficient collaboration between these parties at the time of conceptual design, nor at the detailed design stage. For this reason it is imperative that a designer has sufficient experience and knowledge of construction processes to produce suitably constructible designs. In principle, constructability issues can be regarded as the result of poor coherence, and thus poor communication, between construction and design. The problem therefore lies in the transfer of knowledge between project participants, which can be described as poor knowledge management, in particular, of constructability knowledge. This research aims to address the topic of constructability and to demonstrate how structural knowledge management between contractors and designers can lead to improved construction processes. The concept of constructability is defined, through the identification of technical traits to explicitly describe constructability, concurrently with input from industry expertise and professional experience in the field. Knowledge management principles are also studied in detail and the status quo of current knowledge management initiatives in the industry is investigated. The investigations are done through a series of questionnaire surveys, personal interviews and correspondences. The principle conclusions from the study are that designers do not always understand what constitutes a constructible design. Furthermore, although constructability knowledge is found to exist in complex tacit forms, some explicit guiding principles can indeed be formulated to aid designers. In addition, considering the unique characteristics of each project, these guiding principles should be supported by proposed knowledge management initiatives to facilitate structured forums of knowledge sharing between different parties to develop and transfer constructability knowledge. This will assist to accelerate the learning process towards becoming an accomplished designer, and empower the capacity of both designers and contractors to manage constructability problems. / AFRIKAANSE OPSOMMING: Boubaarheidsprobleme veroorsaak ernstige gevolge in die bedryf en hou dikwels oorweldigende bedreigings in vir die suksesvolle lewering van projekte. Boubaarheidsprobleme ontstaan hoofsaaklik as gevolg van „n ontwerp wat nie genoeg kennis van die konstruksiefase behels nie. Gevolglik, word „n verskeidenheid van negatiewe sekondêre effekte geskep tydens die projek uitvoering, wat risikos uiteindelik veroorsaak in aspekte van tyd, geld en kwaliteit. Heirdie navorsing ondersoek die status quo van boubaarhiedsprobleme in Suid Afrika, met spesifieke verwysing na die verhouding tussen konstruksie en ontwerp. Dit is bekend dat geskikte samewerking tussen konsultante en kontrakteurs kan lei tot meer effektiewe bouprosesse, verbeterde bouveiligheid en goedkoper strukturele oplossings. Kontraktuele ooreenkomste laat nie altyd toe vir behoorlike samewerking tussen die partye gedurende ontwerp stadiums nie. Om hierdie rede, is dit noodsaaklik dat „n ontwerper voldoende ervaring en kennis van die konstruksie prosesse bevat, om behoorlike boubare ontwerpe te kan poduseer. In beginsel, kan boubaarheidsprobleme beskou word as „n gevolg van swak kommunikasie tussen konstruksie en ontwerp. Die problem lê dus in die oordrag van kennis tussen projek deelnemers, wat ook beskryf kan word as swak kennis-bestuur, in die geval, van boubaarheidskennis. Hierdie navorsing beoog om die onderwerp van boubaarheid aan te spreek en te demonstreer hoe strukturele kennis-bestuur tussen die kontrakteurs en ontwerpers tot verbeterde konstruksie prosesse kan lei. Die konsep van boubaarheid word gedefinieer, deur die idenfisering van tegniese eienskappe wat boubaarheid eksplisiet kan beskryf, gelyktydig met die insette van industrie kundigheid en professionele ondervinding. Kennis-bestuur beginsels word ook in diepte bestudeer en die status quo van die huidige kennis-bestuur inisiatiewe in die bedryf word ondersoek. Die ondersoeke word gedoen deur middel van vraelys opnames, persoonlike onderhoude en korrespondensies. Die algemene gevolgtrekkings uit die studie is dat ontwerpers nie altyd die implikasies van „n boubare ontwerp verstaan nie. Verder, alhoewel boubaarheidskennis bestaan in komplekse vorms in die gedagtes van konstruksie personeel, eksplsiete riglyne kan wel geformuleer word om die ontwerp prosses to steun. Aangesien projekte uniek is, moet hierdie riglyne ondersteun word deur die voorestelde kennis-bestuur inisiatiewe, om oop platforms van kennis oordrag te fasiliteer tussen verskillende partye. Dit sal help om die leer prosess te versnel en sal die kapasiteit van beide ontwerpers en kontrakteurs bemagtig, sodat hulle boubaarheidsprobleme beter te kan hanteer.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: See item for abstract / AFRIKAANSE OPSOMMING: Sien item vir opsomming

ENGLISH ABSTRACT: Current understanding of the hydraulic stability of a stacked geotextile tube structure under wave attack is limited. Failure mechanisms that lead to instability are complicated and there is, as yet, no generic approved design method. 2D physical modelling in the large wave/current flume of the Stellenbosch University was done to test various set-up and hydraulic conditions to determine the hydraulic stability of a stacked geotextile tube structure against wave attack. Sixty-five test runs of approximately 1,000 waves each were run. Modelling was done on two different scales that had good similitude, despite the fact that the same geotextile and fill material were used in both. The results provided by the physical modelling gave wave conditions larger than anticipated for hydraulic stability. It was found that the term ―failure‖ was too loosely defined in most cases and that, depending on the definition of structure failure the severity of the wave conditions at failure increased substantially. Sliding was found to be the key failure mechanism for a structure constructed from stacked, 80% sand filled, geotextile tubes. The crest tube receives the most severe loading and is the critical tube in the structure. Structures with double tube crests were found to be negligibly more stable than structures with single tube crests, but reduce energy transmission to the leeside of the structure. Impact loading of the structure combined with wave transmission over the structure explained the wave force on the crest tube of the structure. A modified Goda (1974) method incorporating a wave reduction factor for wave transmission and an angle descriptive of the crest tube position were used. The descriptive angle was derived from results obtained from the physical modelling. The use of this method provides results that correlate well with those found in the physical modelling and with results obtained in previous research. The method has the additional advantage that it is less constrained by limitations for application than those of previous studies / AFRIKAANSE OPSOMMING: Die begrip van die hidroliese stabiliteit van ‘n struktuur gebou uit gepakte geotekstielsandbuise teen golf aanval, is tans beperk. Faal meganismes wat lei tot die onstabiliteit van ‘n struktuur is ingewikkeld en daar is geen generiese aanvaarde ontwerp metode tans in gebruik nie. 2D fisiesemodellering is in die groot golfkanaal van die Universiteit Stellenbosch uitgevoer. ‘n Verskeidenheid van struktuur-uitlegte en hidroliese toestande is getoets om die hidroliese stabiliteit van die struktuur teen golf aanval te bepaal. ‘n Totaal van 65 toetse van ongeveer 1,000 golwe elk is voltooi. Modellering is op twee verskillende skale gedoen, wat goed vergelyk het ten spyte van die feit dat dieselfde geotekstiel en vul materiaal in albei gebruik is. Resultate verkry vanaf die fisiese modellering het groter as verwagte golftoestande vir hidroliese stabiliteit gegee. Dit is gevind dat die definisie van faal (mislukking) in die meeste gevalle swak beskryf is en dat, afhangende van wat as faal van die struktuur beskou word, die golftoestande aansienlik beïnvloed word. Die skuif van die buise is die hoof faal meganisme vir ‘n gepakte geotekstielbuis-struktuur met ‘n vulpersentasie van 80%. Die buis op die kruin van die struktuur word die swaarste belas en is die kritiese buis in die struktuur. Strukture met dubbel buis kruine is onbeduidend meer stabiel as dié met slegs ‘n enkele buis as kruin. Die energie wat na die lysy van die struktuur oorgedra word, is egter beduidend minder. Impak belasting van die struktuur gekombineer met golf-transmissie oor die struktuur, verduidelik die stabiliteit van die buis op die kruin van die struktuur. ‘n Gemodifiseerde Goda (1974) metode met ‘n golfverminderigs faktor word gebruik om golf-transmissie oor die struktuur te akkommodeer, saam met ‘n hoek wat beskrywend is van die posisie van die kruin buis. Die beskrywende hoek is afgelei uit resultate verkry uit die fisiesemodellering. Hierdie metode gee resultate wat goed korreleer met dié verskaf deur die fisiese modellering en die resultate van vorige navorsing oor geotekstielbuis stabiliteit. Die metode het ‗n bykomende voordeel deurdat dit minder begrens is deur beperkings m.b.t. toepassing as die van vorige studies.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The design of steel structures needs to incorporate some optimisation procedure that evolves the initial design into a more economic nal design, where this nal design must still satisfy all the initial design criteria. A candidate optimisation technique suggested by this research is the genetic algorithm. The genetic algorithm (GA) is an optimisation technique that was inspired by evolutionary principles, such as the survival of the ttest (also known as natural selection). The GA operates by generating a population of individuals which 'compete' with one another in order to survive, or di erently stated, in order to make it into the next generation. Each individual presents a solution to the problem. Surviving solutions which propagate through to the next generation are typically 'better' or ' tter' than the ones that had died o , hence suggesting a process of optimisation. This process continues until a de ned convergence criteria is met (e.g. speci ed maximum number of generations is reached), where after the best individual in the population serves as the ultimate solution to the problem. This study thoroughly investigates the inner workings that drive the algorithm, after which an algorithm is presented to face the challenges of structural optimisation. This algorithm will be concerned only with sizing optimisation; geometry, topology and shape optimisation is outside the scope of this research. The objective of this optimising problem will be to minimise the weight of the structure, it is assumed that the weight is inversely propotional to the cost of the structure. The motive behind using a genetic algorithm in this study is largely due to its ability to handle discrete search spaces; classical search methods are typically limited to some form of gradient search technique for which the search space must be continuous. The algorithm is also preferred due to its ability to e ciently search through vast search spaces, which is typically the case for a structural optimisation problem. The genetic algorithm's performance will be examined through the use of bench-marking problems. Benchmarking is done for both planar and space trusses; the 10 - and 25 bar truss problems. Such problems are typically analysed with stress and displacement constraints. After the performance of the algorithm is validated, the study commences towards solving real life practical problems. The rst step towards solving such problems would be to investigate the 160 bar truss benchmarking problem. This problem will be slightly adapted by applying South African design standards to the design, SANS (2005). This approach is more realistic, when compared to simply specifying stress and displacement constraints due to the fact that an element cannot simply be assigned the same stress constraint for tension and compression; slenderness and buckling e ects need to be taken into account. For this case, the search space will no longer simply be some sample search space, but will consist of real sections taken from the Southern African Steel Construction Handbook, SAISC (2008). Finally, the research will investigate what is needed to optimise a proper real life structure, the Eskom Self-Supporting Suspension 518H Tower. It will address a wide variety of topics, such as modelling the structure as realistically as possible, to investigating key aspects that might make the problem di erent from standard benchmarking problems and what kind of steps can be taken to over-come possible issues and errors. The algorithm runs in parallel with a nite element method program, provided by Dr G.C. van Rooyen, which analyses the solutions obtained from the algorithm and ensures structural feasibility. / AFRIKAANSE OPSOMMING: Die ontwerp van staal strukture moet 'n sekere optimalisasie proses in sluit wat die aanvanklike ontwerp ontwikkel na 'n meer ekonomiese nale ontwerp, terwyl die nuwe ontwerp nog steeds aan al die aanvanklike ontwerp kriteria voldoen. 'n Kandidaat optimeringstegniek wat voorgestel word deur hierdie navorsing is die genetiese algoritme. Die genetiese algoritme (GA) is 'n optimaliserings tegniek wat ge- ïnspireer was deur evolusionêre beginsels soos die oorlewing van die sterkste (ook bekend as natuurlike seleksie). Dit werk deur die skep van 'n bevolking van individue wat 'kompeteer' met mekaar om dit te maak na die volgende generasie. Elke individu bied 'n oplossing vir die probleem. Oorlewende oplossings wat voortplant deur middel van die volgende generasie is tipies 'beter' of ' kser' as die individue wat uitgesterf het, dus word 'n proses van optimalisering word saamgestel. Hierdie proses gaan voort totdat 'n bepaalde konvergensie kriteria voldoen is (bv. 'n gespesi seerde aantal generasies), waar na die beste individu in die bevolking dien as die uiteindelike oplossing vir die probleem. Hierdie studie ondersoek die genetiese algoritme, waarna 'n algoritme aangebied word om die uitdagings van strukturele optimalisering aan te spreek. Hierdie algoritme het alleenlik te doen met snit optimalisering; meetkunde, topologie en vorm optimalisering is buite die bestek van hierdie navorsing. Die motief agter die gebruik van 'n genetiese algoritme in hierdie studie is grootliks te danke aan sy vermoë om diskrete soek ruimtes te hanteer; klassieke soek metodes word gewoonlik beperk tot 'n vorm van 'n helling tegniek waarvoor die soektog ruimte deurlopende moet wees. Die algoritme is ook gekies as gevolg van sy vermoë om doeltre end deur groot soektog ruimtes te soek, wat gewoonlik die geval vir 'n strukturele probleem met optimering is. Die genetiese algoritme se prestasie sal ondersoek word deur die gebruik van standaarde toetse. Standarde toetse word gedoen vir beide vlak en ruimte kappe, die 10 - en 25 element vakwerk. Sulke probleme word tipies met spanning en verplasing beperkings ontleed. Na a oop van die bekragtiging van die algoritme, word praktiese probleme hanteer. Die eerste stap in die rigting sou wees om die 160 element vakwerk toets probleem te ondersoek. Hierdie probleem sal e ens aangepas word deur die toepassing van die Suid-Afrikaanse ontwerp standaarde, SANS (2005) aan die ontwerp. Dit is 'n meer realistiese benadering in vergelyking met net gespesi seerde spanning en verplasing beperkings as gevolg van die feit dat 'n element nie net eenvoudig dieselfde spanning beperking vir spanning en druk toegeken kan word nie; slankheid en knik e ekte moet ook in ag geneem word. In hierdie geval sal die soek ruimte nie meer net meer eenvoudig 'n sekere teoretiese soek ruimte wees nie, maar sal bestaan uit ware snitte wat uit die Suid Afrikaanse Konstruksie Handboek kom, SAISC (2008). Ten slotte sal die navorsing ondersoek instel na 'n standaard Eskom Transmissie toring en dit sal 'n wye verskeidenheid van onderwerpe aanspreek, soos om die modellering van die struktuur so realisties as moontlik te maak, tot die ondersoek van sleutelaspekte wat die probleem verskillend van standaard toets probleme maak en ook watter soort stappe geneem kan word om moontlike probleme te oor-kom. Die algoritme werk in parallel met 'n eindige element metode program, wat deur Dr GC van Rooyen verskaf is, wat die oplossings ontleed van die algoritme en verseker dat die struktuur lewensvatbaar is.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Natural fibre reinforced concrete (NFRC) is a type of concrete that has become of particular interest in recent years, due to its potential for being used as a sustainable and economically viable building material. Natural fibres are often cheap and widely available in developing nations. Sisal is one such fibre predominantly grown in Brazil and has been identified as having the potential to be commercially cultivated in Southern Africa. The durability of sisal fibres in a cementitious environment tends to be adversely affected due to the high alkalinity of pore water and the presence of calcium hydroxide. This research dealt with the use of sisal fibre reinforced concrete (SFRC) blocks. It focused on the mechanical and volumetric properties of blocks with varying fibre and condensed silica fume content (CSF). Two different SFRC blocks were produced (solid and hollow) using an average fibre length of 10 mm. Two matrix types were used: one using a 70:30 cement:fly-ash ratio and another using a 60:30:10 cement:fly-ash:CSF ratio by weight. Samples of each matrix type were prepared with 0, 0.5 and 1% fibre content by volume. Hollow blocks were tested for compressive strength and capillary water absorption, while solid blocks were tested for compressive strength, flexural strength, capillary water absorption, dimensional stability, drying shrinkage, density, total water absorption and void content. All tests were performed on samples with an age of 28 days. Solid block compressive tests were also performed on samples with an age of 7 days. The hollow blocks had significantly lower average compression strength than the solids, but an increase in fibre content caused a slight increase in strength. For solid blocks, it was found that the addition of natural fibres decreases the strength, although a partial substitution of cement with CSF, in conjunction with fibres, did increase the strength relative to blocks without CSF. The flexure strength was also lowered somewhat by the addition of fibres, but an increase in ductility was noted, although not quantified. The addition of CSF to fibre-containing blocks led to an increase in capillary water absorption, but a decrease in absorption through immersion. This shows that the addition of CSF does significantly alter the pore system of a cementitious matrix reinforced with natural fibres. Also, the dimensional stability increased with the addition of CSF and fibres. The same can be said for drying shrinkage. Even though an increase in fibre and CSF caused samples to shrink more under drying, they were more stable under cycles of wetting and drying. It was concluded that the addition of fibres to a matrix had a detrimental effect on strength, although ductility did increase. The volumetric properties of concrete were also adversely affected by the addition of fibres, although dimensional stability was improved. The partial substitution of cement with CSF did improve many of the mechanical and volumetric properties of samples containing sisal fibre. / AFRIKAANSE OPSOMMING: Natuurlike vesel bewapende beton (NVBB) is ’n tipe beton wat onlangs heelwat belangstelling ontlok het weens die potensiaal om gebruik te word as ‘n volhoubare en ekonomiese haalbare boumateriaal. Natuurlike vesels is dikwels baie goedkoop en wyd beskikbaar in ontwikkelende lande. Sisal is een so ‘n vesel wat verkry word vanaf die blare van ’n garingboom. Die plant word hoofsaaklik in Brasilië verbou en is al uitgewys weens sy potensiaal om op kommersiële skaal in Suidelike Afrika verbou te word. Die duursaamheid van sisal vesels is geneig om nadelig geaffekteer te word in die teenwoordigheid van kalsium hidroksied en ’n hoë-alkali omgewing, soos gevind in die porie-water van beton. Hierdie navorsing handel oor die gebruik van sisal vesel bewapende beton (SVBB) boublokke. Dit fokus op die meganiese- en duursaamheids eienskappe van blokke met verkillende inhoude van vesel en gekondenseerde silika dampe (GSD). Twee verskillende SVBB blokke is geproduseer (solied en hol) deur gebruik te maak van 10 mm vesels. Twee matriks tipes is gebruik: een met ’n 70:30 sement:vliegas verhouding en een met ’n 60:30:10 sement:vliegas:GSD verhouding, volgens gewig. Blokke van elke matriks tipe is geproduseer met 0, 0.5 en 1% vesel inhoud, volgens volume. Hol blokke is getoets vir druksterkte en kapillêre water absorpsie, terwyl soliede blokke getoets is vir druksterkte, buigsterkte, kapillêre water absorpsie, dimensionele stabiliteit, krimp onder uitdroging, digtheid, totale water absorpsie en luginhoud. Alle toetse is gedoen op blokke met ’n ouderdom van 28 dae. Druktoetse is ook gedoen op soliede blokke met ’n ouderdom van 7 dae. Die hol blokke het ’n aansienlike laer gemiddelde druksterkte as die soliede blokke gehad, maar ’n toename in veselinhoud het gelei tot ’n effense verhoging in druksterkte. ’n Toename in veselinhoud van soliede blokke het gelei tot ’n afname in druksterkte, alhoewel ’n gedeeltelike vervanging van sement met GSD gelei het tot ’n hoër druksterkte vir blokke met vesels. Die buigsterkte van soliede blokke het ook afgeneem met ’n verhoging in veselinhoud. ’n Verhoging in duktiliteit is waargeneem met ’n toename in veselinhoud, alhoewel dit nie gekwantifiseer is nie. Die toevoeging van GSD tot blokke bevattende vesels het gelei tot ’n verhoging in kapillêre water absorpsie, maar ’n verlaging in totale water absorpsie. Dit kan daarop wys dat die toevoeging van GSD die poriestelsel van NVBB noemenswaardig verander. Beide die dimensionele stabiliteit en krimp onder uitdroging het toegeneem met die toevoeging van GSD en vesels tot die blokke. Dus, die toevoeging het gelei tot ’n hoër krimpvervorming tydens uitdroging en ’n hoër stabiliteit tydens nat/droog siklusse. Daar is tot die gevolgtrekking gekom dat die toevoeging van sisal vesels tot ’n beton blok oor die algemeen ’n negatiewe effek het op sterkte, alhoewel duktiliteit toeneem. Die volumetriese eienskappe van beton word ook negatief geaffekteer met die toevoeging van sisal vesels, alhoewel dimensionele stabiliteit verbeter. Die gedeeltelike vervanging van sement met GSD lei tot die verbetering van beide meganiese en volumetriese eienskappe van beton blokke wat sisal vesels bevat.

Thesis (MscEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Low-rise buildings with crest fastenedmetal cladding are susceptible to failures in the vicinity of the fasteners during strongwind uplift conditions. These localised failures often lead to the progressive removal of cladding, which can cause disastrous building damage. In South Africa, the current metal cladding design approach is inadequate, since it solely relies upon manufacturer design specifications. These specifications are typically designated as broad design guidelines for the maximum allowable cladding support spacings which are independent from any specified design loads. This research focuses on the investigation of 0.50 mm ISQ550 IBR cladding systems to understand basic cladding behaviour during static wind uplift conditions and to quantify the uplift performance of IBR systems. The research investigation also included the improvement and performance evaluation of a full-scale cladding test method which applies an air-bag loading method to simulate static wind uplift conditions according to the revised SANS 10237:201X code of practice. This thesis may serve as a basis for further cladding research, and the development of suitable standardised metal cladding test methods in South Africa. Several experimental investigation methods and limited finite element analyses (FEA) were used to investigate IBR and the performance of the test methods. Tensile testing was used to determine the material properties of the cladding metal. The full-scale cladding assembly testing was used to investigate the behaviour of IBR and to evaluate the performance of the air-bag test rig. The localised behaviour of the cladding around the fasteners was also investigated with a small cladding subassembly test method. The FEA served as a supplementary investigation for IBR performance evaluation. The experimental investigation confirmed that the static wind uplift resistances of IBR systems are mainly governed by localised deformations of their fastened crests and fastener pull-through failures. The behaviour and performance of IBR systems are heavily dependent on the crest fastening arrangement. IBR systems with every crest fastening demonstrated a considerably higher wind uplift resistance than IBR systems with the standard alternate crest fastening arrangement. The measured fastener loads were independent from span length, whereas the overall uplift resistance of IBR reduced with increased span lengths. Load-span resistance data for 0.50 mm ISQ550 IBR was derived from testing to provide a rational framework for design. The FEA provided a reasonable simulation of IBR subjected to static wind uplift and confirmed the presence of high stress and strain concentrations around the fastener holes which cause fastener pull-through failures. Therefore, FEA can be used as an effective tool to investigate the behaviour of IBR. In conclusion, the air-bag test method used in this research investigation provided an effective method for evaluating the uplift performance of crest fastened metal cladding. However, the air-bag load method is not capable of accurately simulating a true uniformly distributed uplift load. It is recommended that direct air pressure testing be adopted for any further research or commercial testing ofmetal cladding because direct air pressure testing is an effective and proven test method for accurate simulation of static and cyclic wind uplift conditions. / AFRIKAANSE OPSOMMING: Metaalbekleding met kruinvashegting op lae geboue is geneig om te faal by die vashegters tydens toestande van sterkwind-opheffing. As vashegters faal kan bekleding progressief verwyderwordomrampspoedige skade aan die gebou te veroorsaak. Die huidige ontwerpmetode vir metaalbekleding in Suid-Afrika is onvoldoende, aangesien dit slegs gegrond is op vervaardigers se ontwerpspesifikasies. Spesifikasies word gewoonlik verklaar as breë ontwerpriglyne vir die maksimum toelaatbare spasiërings van ondersteunings sonder enige oorwegings vir ontwerpbelastings. Hierdie navorsing fokus dus op 0.50mm ISQ550 IBR metaalbekleding omdie basiese gedrag van bekleding tydens wind-opheffing beter te verstaan en die ophefweerstand van IBR te kwantifiseer vir ontwerpdoeleindes. Verder ondersoek hierdie navorsing ook die verbetering en evaluasie van ’n volskaalse bekledingstoetsmetode wat statiese wind-opheffing naboots met verspreide lugsakbelasting volgens die hersiende SANS 10237:201X gebruikskode. Hierdie proefskrif kan dien as ’n grondslag vir verdere navorsing en die ontwikkeling van geskikte standaard-toetsmetodes vir metaalbekleding in Suid-Afrika. Verskeie eksperimentele toetsmetodes en beperkte eindige-element-analises (EEA) is gebruik om die gedrag van IBR en die toets-opstellings te ondersoek. Trektoetse is gebruik om die meganiese eienskappe van die bekledingsmetaal te bepaal. Volskaalse toets-opstellings is gebruik om die weerstand van IBR te ondersoek en die lugsaktoetsmetode te evalueer. Die gelokaliseerde gedrag van die bekleding rondom die vashegters was ook ondersoek met klein toets-opstellings. EEA het gedien as ’n aanvullende ondersoek om die gedrag van IBR te evalueer. Die eksperimentele ondersoek het bevestig dat die wind-ophefweerstande van IBR-stelsels hoofsaaklik bepaal word deur gelokaliseerde deformasies van die vasgehegde kruine en die vashegters se deurtrekweerstand. Die gedrag en weerstand van IBR-stelsels is ook grootliks afhanklik van die toegepaste vashegtingsmetode. IBR stelsels met vashegting deur elke kruin het ’n hoër ophefweerstand verskaf as IBR-stelsels met die standaard vashegtingsmetode deur elke tweede kruin. Die gemete vashegterbelastings was onafhanklik van die spanlengtes, terwyl die algehele ophefweerstand van IBR verminder het vir langer spanlengtes. Toetsdata is gebruik om ophefweerstande vir 0.50mm ISQ550 IBR oor verskeie spanlengtes af te lei sodat ’n rasionele raamwerk vir ontwerp bewerkstellig kan word. Die EEA het die gedrag van IBR tydens toestande van statiese wind-opheffing redelik goed nageboots en het ook die teenwoordigheid van hoë spannings- en vervormingskonsentrasies rondom die vashegtergate, wat vashegters laat deurtrek, bevestig. Daarom kan EEA as ’n effektiewe instrument gebruik word om die gedrag van IBR te ondersoek. Ten slotte word dit afgelei dat die lugsaktoetsmetode van hierdie navorsingsondersoek ’n effektiewe metode verskaf het vir die gedrag-evaluering van kruinvasgehegte bekleding tydens wind-opheffing. Die lugsaktoetsmetode kan egter nie ’n ware gelykverspreide ophefbelasting naboots nie. Daarom word dit voorgestel dat toetsmetodes wat direkte lugdruk aanwend gebruik moet word vir enige verdere navorsing of kommersiële toetse van metaalbekleding, aangesien dit ’n effektiewe en bevestigde toetsmetode is wat statiese en sikliese opheftoestande akkuraat kan naboots.

Thesis (MScEng)--Stellenbosch University, 2013. / Cellular concrete is a type of lightweight concrete that consists only of cement, water and sand with 20 per cent air by volume or more air entrained into the concrete. The two methods used for air entrainment in cellular concrete are (1) the use of an air entraining agent (AEA), and (2) the use of pre-formed foam. If pre-formed foam is used to entrain air into the concrete the concrete is named foamed concrete and if an AEA is used the concrete is termed aerated concrete. Depending on the type of application, structural or nonstructural, cellular concrete can be designed to have a density in the range of range of 400 to 1800 kg/m3. Non-structural applications of cellular concrete include void and trench filling, thermal and acoustic insulation. Structural applications of cellular concrete include pre-cast units such as concrete bricks, partitions, roof slabs etc. Due to the high levels of air in cellular concrete it is challenging to produce compressive strengths that are sufficient to classify the concrete as structurally useful when non-autoclaving curing conditions are used. The autoclaving process combines high temperature and pressure in the forming process, which causes higher strength and reduced shrinkage. This process is also limited to prefabricated units. Non-autoclave curing conditions include moist curing, dry curing, wrapping the concrete in plastic, etc. However, now that the world is moving in an energy efficient direction, ways to exclude energy-intensive autoclaving are sought. It has for instance been found that the utilisation of high volumes of fly-ash in cellular concrete leads to higher strengths which make it possible to classify the concrete as structurally useful. Now, that there is renewed interest in the structural applications of the concrete a design methodology using an arbitrary air entraining agent needs to be found. The research reported in this thesis therefore attempts to find such a methodology and to produce aerated concrete with a given density and strength that can be classified as structurally useful. For the mix design methodology, the following factors are investigated: water demand of the mix, water demand of the mix constituents, and the amount of AEA needed to produce aerated concrete with a certain density. The water demand of the mix depends on the mix constituents and therefore a method is proposed to calculate the water demand of the mix constituents based on the ASTM flow turn table. Due to the complex nature of air entrainment in concrete, the amount of air entrained into the concrete mix is not known beforehand, and a trial and error method therefore had to be developed. The trial mixes were conducted in a small bakery mixer. From the trial mixes estimated dosages of AEA were found and concrete mixes were designed based on these mixes. The factors that influence the mix design and strength of aerated concrete include filler/cement ratio (f/c), fly-ash/cement ratio (a/c) and design target density. Additional factors that influence the strength of aerated concrete are specimen size and shape, curing, and concrete age. It was found that the sand type and f/c ratio influence the water demand of the concrete mix. Sand type and f/c ratio also influence compressive strength, with higher strength for a finer sand type and lower f/c ratios. However, the concrete density is the factor that influences the strength the most.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Compaction is one of the key processes in the construction of road pavement layers. Not only is it significant in ensuring the structural integrity of the material in the road layers, but it also has an influence on the engineering properties and performance of the soil material. A poorly compacted material is characterised by low density, high porosity and below standard shear strength. This, as a result causes rutting, moisture susceptibility, potholing, corrugations and passability problems on the road. Therefore, it is vitally important that field compaction is done correctly. For this reason, laboratory compaction methods have been developed to simulate the field compaction process in the laboratory. The Mod AASHTO test has long been used as the laboratory compaction method of choice by virtue of its simplicity and the lack of bulky equipment required. However, previous studies have established that the Modified AASHTO method does not adequately simulate field compaction criteria especially for cohesionless materials. Two reasons have been advanced; The Mod AASHTO compaction method does not adequately simulate the compaction done in the field when the granular mix is laid; The compaction method may cause disintegration of the material. Alternative tests have been considered and much research has focused upon the use of a modified demolition hammer (vibratory hammer) for laboratory compaction of granular materials. This study undertook to evaluate the influence of test factors pertinent to the vibratory hammer compaction method. The influence of these test factors on compaction time and obtainable material density was assessed with the objective of developing a compaction method for granular materials. Vibratory hammer compaction tests were conducted on G3 hornfels, G4 hornfels and G7 sandstone material types and to a lesser extent, reclaimed asphalt (RA). Densities obtained were referenced to Mod AASHTO compaction density. Findings of the study showed that, the mass of the tamping foot has a significant influence on the obtainable compaction density. Other factors such as, moisture content, frequency and frame rigidity were also found to affect compaction with the vibratory hammer. In addition, it is shown that the surcharge load does not significantly influence the obtainable compaction density but does contribute to the confinement of the material and restricts the upward bounce of the hammer. On the basis of the results and findings, a compaction method was proposed, incorporating test parameters and factors that would provide ideal results for a set compaction time. Repeatability tests showed that, the developed vibratory hammer compaction method was effective in compacting graded crushed stone material types (i.e. G3 and G4) and probably RA. The test was not as effective on the G7 material. Further studies on this material (G7) are required. In addition to the previous testing regime, a comparative assessment of the developed vibratory hammer compaction method in relation to the vibratory table method was done. The results show that the vibratory hammer is capable of producing specimens of densities comparable to those of the vibratory table. A sieve analysis undertaken before and after compaction showed that compaction with the developed vibratory hammer compaction method does not result in any significant material disintegration. Based on the results of this study, a specification for the determination of maximum dry density and optimum moisture content of granular material using the vibratory hammer is recommended. / AFRIKAANSE OPSOMMING: Kompaksie is een van die belangrikste prosesse in die konstruksie van die padplaveisel. Dit is nie net waardevol vir die versekering van strukturele integriteit van die materiaal, maar dit het ook 'n invloed op die ingenieurseienskappe en vermoë van die grond materiaal. 'n Swak gekompakteerde materiaal word gekenmerk deur 'n laë digtheid, hoë porositeit, on onvoldoende skuifweerstand. Die kenmerke maak die material vatbaar vir vogen. Lei tot spoorvorming, slaggate, golwe en deurgangs probleme op die pad. Dit is dus uiters noodsaaklik dat veld kompaksie korrek gedoen word. Om hierdie rede, is kompaksie metodes in die laboratorium ontwikkel om sodaend veldkompaksie te simuleer. Die “Mod AASHTO” laboratorium kompaksie toets is die gekose laboratorium kompaksie metode op grond van sy eenvoudigheid en gebruik van minimale toerusting. Vorige studies het egter bevestig dat die “Mod AASHTO”-metode nie veldkompaksie akkuraat kan simuleer nie, veral vir kohesielose materiaal. As gevolg van twee hoofredes; Die Mod AASHTO kompaksiemetode is nie ‘n realistiese en vergelykende simmulering van kompaksie soos dit in die veld gedoen word nie; Die kompaksie metode mag verbrokkeling van die materiaal veroorsaak. Alternatiewe toetse was oorweeg en baie navorsing het gefokus op die gebruik van 'n aangepaste vibrerende hamer. Hierdie studie het onderneem om verskeie relevante toetsfaktore van die vibrerende hamer en hul invloed op die kompaksie en verkrygbare digtheid te bestudeer. Die invloed van hierdie toetsfaktore op kompaksietyd en verkrygbare materiaal digtheid was geassesseer met die doel om 'n kompaksiemetode vir granulêre materiaal te ontwikkel. Vibrerende hammer kompaksietoetse was uitgevoer op G3 hornfels, G4 hornfels en G7 sandsteen materiaal en tot 'n mindere mate herwinde asfalt. Digthede verkry was verwys na die Mod AASHTO kompaksie digtheid. Resultate van die studie het getoon dat die gewig van die stamp voet ‘n merkwaardige invloed het op die verkrygbare kompaksie digtheid. Ander faktore soos voginhoud, frekwensie en raam styfheid het ook getoon om kompaksiedigtheid te beïnvloed met die vibrerende hammer. Benewens was ook getoon dat die toeslaglading geen beduidende invloed het op die verkrygbare kompaksie digtheid nie, maar wel bydrae tot die inperking van die materiaal en verhoed die vertikale terugslag van die hammer. Gebaseer op die resultate en bevindinge was ‘n kompaksiemetode voorgestel wat toets parameters integreer met toetsfaktore en tot volg ideale resultate vir ‘n gegewe kompaksietyd voorsien. Herhaalde kalibrasie toetse het getoon dat die ontwikkelde kompaksiemetode effektief is in die kompaktering van gegradeerde gebreekte klip materiaaltipes (G3 en G4) en moontlik herwanne asfalt. Die toets was nie so doeltreffend op die G7 materiaal nie. Verdere studies op hierdie materiaal (G7) is dus nodig. Addisioneel tot die vorige toets, is bevind dat ‘n vergelykende assesering van die ontwikkelde vibrerende hammer kompaksiemetode in verhouding tot die vibrerende tafel. Die resultate wys dat die vibrerende hammer die vermoë het om toetsmonsters met digthede vergelykbaar met die vibrerende tafel te produseer. Sifanalise voor en na kompaksie het getoon dat verdigting met die ontwikkelde vibrerende hamer kompaksie metode nie lei tot die disintegrasie van die materiaal nie. Gebasseer op die resultate van dié studie was ‘n spesifikasie vir die bepaling van maksimum droé digtheid en optimale voginhoud van granulêre material aangeraai.