Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The building industry is responsible for a substantial contribution to pollution. The production of building materials, as well as the operation and maintenance of structures leads to large amounts of carbon-dioxide (CO2) being release in the atmosphere. The use of renewable resources and construction materials is just one of the ways in which the carbon footprint of the building industry can be reduced. Sisal fibre is one such renewable material. Sisal fibre is a natural fibre from the Agave Sisalana plant. The possibility of incorporating sisal fibre in a cement-based matrix to replace conventional steel and synthetic fibres has been brought to the attention of researchers. Sisal fibre has a high tensile strength in excess of polypropylene fibre and comparable to PVA fibre. Sisal fibre consists mainly of cellulose, hemi-cellulose and lignin. The disadvantage of incorporating sisal fibre in a cement-based matrix is the degradation of the composite. Sisal fibres tend to degrade in an alkaline environment due to changes in the morphology of the fibre. The pore water in a cement base matrix is highly alkaline which leads to the degradation of the fibres and reduced strength of the composite over time. Sisal fibre reinforced cement-based composites (SFRCC) were investigated to evaluate the durability of the composites. Two chemical treatments, alkaline treatment and acetylation, were performed on the fibre at different concentrations to improve the resistance of the fibre to alkaline attack. Alkaline treatment was performed by using sodium hydroxide (NaOH), while acetylation was performed by using acetic acid or acetic anhydride. Single fibre pull-out (SFP) tests were performed to evaluate the influence of chemical treatment on fibre strength, to study the fibre-matrix interaction and to determine a critical fibre length. A matrix consisting of ordinary Portland cement (OPC), sand and water were used for the SFP tests. This matrix, as well as alternative matrices containing fly ash (FA) and condensed silica fume (CSF) as supplementary cementitious material, were reinforced with 1% sisal fibre (by volume) cut to a length of 20 mm. The OPC matrix was reinforced with untreated- and treated fibre while the alternative matrices were reinforced with untreated fibre. Alternative matrices containing varying fibre volumes and lengths were also produced. Three-point bending- (indirect), direct tensile- and compression tests were performed on specimens at an age of 28 days to determine the strength of the matrix. The remainder of the specimens were subjected to ageing by extended curing in water at 24˚C and 70˚C respectively and by alternate cycles of wetting and drying, after which it was tested at an age of 90 days from production to evaluate the durability of the fibre. An increase in fibre volume led to a decrease in compressive strength and peak tensile strength. The optimum fibre length at a volume of 1% was 20 mm for which the highest compression strength was recorded. The combination of alkali treatment and acetylation was the most effective treatment condition, followed by alkali treatment at low concentrations of sodium hydroxide. At higher concentrations of sodium hydroxide, a significant reduction in strength was recorded. The addition of supplementary cementitious materials also proved to be effective in mitigating degradation, especially in the cases where CSF was used. FA proved to be less effective in reducing the alkalinity of the matrix. However, the use of FA as fine filler resulted in higher strengths. Specimens manufactured by extrusion did not have superior mechanical properties to cast specimens. The conclusion was made that the use of sisal fibre in a cement-based matrix is effective in providing ductile failure. Chemical treatment and the addition of supplementary cementitious materials did improve the durability of the specimens, although degradation still took place. / AFRIKAANSE OPSOMMING: Die boubedryf is verantwoordelik vir 'n aansienlike bydrae tot besoedeling. Die produksie van boumateriale, sowel as die bedryf en instandhouding van strukture lei tot groot hoeveelhede koolstof dioksied (CO2) wat in die atmosfeer vrygestel word. Die gebruik van hernubare hulpbronne en boumateriale is maar net een van die maniere waarop die koolstof voetspoor van die boubedryf verminder kan word. Sisal vesels is 'n voorbeeld van 'n hernubare materiaal. Sisal vesel is 'n natuurlike vesel afkomstig vanaf die Agave Sisalana plant. Die moontlikheid om sisal vesels in 'n sement gebasseerde matriks te gebruik om konvensionele staal en sintetiese vesels te vervang, is tot die aandag van navorsers gebring. Sisal vesel het 'n hoër treksterkte as polipropileen vesels en die treksterkte vergelyk goed met die van PVA vesels. Sisal vesel bestaan hoofsaaklik uit sellulose, hemi-sellulose en lignien. Die nadeel verbonde aan die gebruik van sisal vesels in 'n sement gebasseerde matriks is die degradasie van die komposiet. Sisal vesels is geneig om af te breek in 'n alkaliese omgewing as gevolg van veranderinge wat in die morfologie van die vesel plaasvind. Die water in die porieë van 'n sement gebasseerde matriks is hoogs alkalies wat lei daartoe dat die vesel afgebreek word en die sterkte van die komposiet afneem oor tyd. Sisal vesel versterkte sement gebasseerde komposiete is ondersoek om die duursaamheid van die komposiete te evalueer. Twee chemiese behandelings, alkaliese behandeling en asetilering, is uitgevoer op die vesels teen verskillende konsentrasies om die weerstand van die vesels teen alkaliese aanslag te verbeter. Alkaliese behandeling was uitgevoer met natrium-hidroksied (NaOH) terwyl asetilering met asynsuur en asynsuurhidried uitgevoer is. Enkel vesel uittrek toetse is uitgevoer om die invloed van chemiese behandeling op veselsterkte te evalueer, om die vesel/matriks interaksie te bestudeer en om die kritiese vesellengte te bepaal. 'n Matriks wat uit gewone Portland sement (OPC), sand en water bestaan, is gebruik vir die enkel vesel uittrek toetse. Dieselfde matriks, sowel as alternatiewe matrikse wat vliegas (FA) en gekondenseerde silika dampe (CSF) as aanvullende sementagtige materiaal bevat, is versterk met 1% vesel (by volume) wat 20 mm lank gesny is. Die OPC matriks was versterk met onbehandelde- en behandelde vesels, terwyl die alternatiewe matrikse met onbehandelde vesels versterk is. Matrikse wat wisselende vesel volumes en lengtes bevat het is ook vervaardig. Drie-punt buigtoetse (indirek), direkte trek toetse en druktoetse is uitgevoer op proefstukke teen 'n ouderdom van 28 dae om die sterkte van die matriks te bepaal. Die oorblywende proefstukke is onderwerp aan veroudering deur verlengde nabehandeling in water teen 24˚C en 70˚C onderskeidelik en deur afwissilende siklusse van nat- en droogmaak waarna dit op 'n ouderdom van 90 dae vanaf vervaardiging getoets is om die duursaamheid van die matriks te evalueer. 'n Toename in vesel volume het tot 'n afname in druksterkte en piek treksterkte gelei. Die optimum vesel lengte teen 'n volume van 1% was 20 mm, waarvoor die hoogste druksterkte opgeteken is. Die kombinasie van alkaliese behandeling en asetilering was die mees effektiewe behandeling, gevolg deur alkaliese behandeling by lae konsentrasies natrium-hidroksied. Vir hoë konsentrasies natrium-hidroksied is 'n aansienlike afname in sterkte opgeteken. Die toevoeging van aanvullende sementagtige materiale was ook effektief om die degradadering van die vesels te verminder, veral in die gevalle waar CSF gebruik is. FA was minder effektief om die alkaliniteit van die matriks te verminder. Die gebruik van FA as fyn vuller het nietemin hoër sterkte tot gevolg gehad. Proefstukke wat deur ekstrusie vervaardig is, het nie beter meganiese eienskappe gehad as proefstukke wat gegiet is nie. Daar is tot die gevolgtrekking gekom dat sisal vesel in 'n sement gebasseerde matriks wel effektief is om 'n duktiele falingsmode te voorsien. Chemiese behandeling en die toevoeging van aanvullende sementagtige materiale het die duursaamheid van die proefstukke verbeter, alhoewel degradering steeds plaasgevind het.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Science in Engineering

published_or_final_version / Civil Engineering / Master / Master of Science in Engineering

published_or_final_version / Civil Engineering / Master / Master of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Philosophy

Major advances have been observed during the last two decades in the field of seismic engineering with further refinements of performance-based seismic design philosophies and the subsequent definition of corresponding compliance criteria. Following the globally recognized expectation and ideal aim to provide a modern society with high (seismic) performance structures able to sustain a design level earthquake with limited or negligible damage, alternative solutions have been developed for high-performance, seismic resisting systems. In the last two decades, an alternative approach in seismic design has been introduced for precast concrete buildings in seismic regions with the introduction of “dry” jointed ductile systems also called “hybrid” systems based on unbonded post-tensioned rocking connections. As a result structural systems with high seismic performance capabilities can be implemented, with the unique capability to undergo inelastic displacement similar to their traditional monolithic counterparts, while limiting the damage to the structural system and assuring full re-centring capabilities (negligible residual or permanent deformations). The continuous and rapid development of jointed ductile connections for seismic resisting systems has resulted in the validation of a wide range of alternative arrangements, encompassed under the general umbrella of “hybrid” systems. This research provides a comprehensive experimental and analytical investigations of 2- and 3-Dimensional, 2/3 scaled, exterior beam-column joints subjected both uni and bi-directional (four clove) quasic-static loading protocols into the behaviour, modelling, design and feasibility of new arrangements for “dry” jointed ductile systems for use in regions of high seismicity. In order to further emphasize the enhanced performance of these systems, a comparison with the experimental response and observed damage of 2-D and 3-D monolithic beam-column benchmark specimens is presented. However, after a lot of attention given to the behaviour of the skeleton structure, more recently the focus of research in Earthquake Engineering has concentrated on the behaviour of the floor system within the overall 3D behaviour of the building and the effects of beam elongation. The effects of beam elongation in precast frame systems have been demonstrated to be a potential source of un-expected damage, unless adequate detailing is provided in order to account for displacement incompatibilities between the lateral resisting systems and the floor. Two contributions to beam elongation are typically recognized: a) the material contribution due to the cumulative residual strain within the steel, and b) the geometrical contribution due to the presence of a neutral axis and actual depth of the beam. Regarding jointed ductile connections with re-centering characteristics, the extent of beam elongation is significantly reduced, being limited to solely the geometrical contribution. Furthermore, such effects could be minimized when a reduced depth of the beam is adopted due to the use of internal prestressing or external post-tensioning. However, damage to precast floor systems, resulting from a geometric elongation of the beam, has yet to be addressed in detail. In order to emphasize the enhanced performance in controlling and minimizing the damage of the structural elements via the use of the proposed advanced hybrid solutions, this research presents via experimental and analytical validation of two alternative and innovative solutions to reduce the damage to the floor using 2 and 3-Dimensional, 2/3 scaled, exterior beam-column joints. The first approach consists of using standard precast rocking/dissipative frame connections (herein referred to as “gapping”) in combination with an articulated or “jointed” floor. This system uses mechanical devices to connect the floor and the lateral beams which can accommodate the displacement incompatibilities in the connection. The second approach to reduce the floor damage investigates the implementation of a “non-gapping” connection, also called non-tearing-floor connection, using a top hinge at the beam-column interface, while still relying on more traditional floor-to-frame connections (i.e. topping and continuous starter bars). Additionally, further refinements and constructability issues for the non gapping connection are investigated under the experimental and analytical validation of a major 2-Dimensional, 2/3 scaled, two-story one-bay frame using non-tearing floor connections. Based on the non-tearing floor connections, a series of parametric analysis for beam-column joints and frames are carried out. Furthermore, the analysis and design of two prototype frames using different solutions is presented. The frames are subjected to cyclic adaptive pushover and inelastic time history analysis in order to investigate analytically the response characteristics of hybrid frames using non-tearing connections, as well as how the beam growth affects the frame response under earthquake loading. Computational models for hybrid PRESSS frames and a conventional reinforced concrete frames are developed and compared with the ones using non-tearing connections.

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