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The most used widely material in the construction and industrial industry is concrete. Concrete is a material that has been used for a long time and will remain to do so. Therefore, it is especially important to obtain knowledge of the material’s properties and how it is affected by various conditions. A major problem with concrete is cracking that occurs when its shrinkage is prevented. When a concrete wall is cast against ground, shrinkage occurs. The cracks that develop due to this can cause leaks and reinforcement corrosion that not only reduces the lifespan of the concrete, but are also making it aesthetically ugly. One solution to reduce the restraint is to divide the casting into stages. This study contains investigation whether a thoughtful stage casting is a method that can theoretically and practically affect the shrinkage restraint and thereby the cracking in concrete walls. This report observes the tensile stresses in a 15 meter long concrete wall with strength class C30/37. The wall is exposed for two different relative humidity circumstances, indoor environment which gives 50% and outdoor environment which gives 80%. The analysis comprises four different casting methods for a wall; casting in one piece and three casting methods according to thoughtful stage casting. The contemplated time range between the casting stages is normal production time, 30 days, and extended production time, 60 days. At first the calculations for shrinkage and creep of the concrete had to be done according to Eurocode 2. The results from the calculations are thereafter used in the finite element program FEM-Design from the company Strusoft. The results in the report demonstrates the tensile stresses that arise in a 15 meter long wall without the stages and when the casting is done with thoughtful stages. A variation of the foundation depth consisting of non-cohesive soil is also presented for one of the casting methods. The conclusion of the results is that stage casting is a solution to reduce restraint and thereby stresses in concrete walls. The results reveal that the tensile stresses are reduced with the highest value of approximately 80%. The efficiency of casting into stages is possible and practicable within a normal production time. / Det mest använda materialet i anläggnings- och industribranschen är betong. Betong är ett material som har använts länge och kommer fortsätta att användas. Därför är det främst viktigt att ha kunskap om materialets egenskaper och hur det påverkas av olika förhållanden. Ett stort problem med betong är sprickbildning när dess krympning förhindras. När en betongvägg gjuts mot ett underlag förekommer krymptvång. Sprickorna som uppstår på grund av detta kan orsaka läckage och armeringskorrosion som minskar betongens livslängd och är dessutom estetiskt fula. Ett sätt att minska tvånget är att dela in gjutningen i etapper. I detta arbete undersöks om en genomtänkt gjutetappsindelning är en metod som teoretiskt och praktiskt kan påverka krymptvånget och därmed sprickbildningen i betongväggar. Denna rapport betraktar dragspänningarna i en 15 meter lång betongvägg med hållfasthetsklassen C30/37. Väggen utsätts för två olika relativa luftfuktighetsförhållanden, inomhusmiljö samt utomhusmiljö vilket ger ett värde på 50% och 80%. Analyserna omfattar fyra olika gjutningsmetoder för väggen; gjutning utan etappindelning samt gjutning utförd enligt tre genomtänkta etappindelningar. Tiden som betraktas mellan gjutetappsindelningarna begränsas till normal produktionstid, 30 dagar, och en förlängd produktionstid, 60 dagar. Först utförs handberäkningar enligt Eurokod 2 på betongens krympning och krypning för att sedan sätta in resultaten i finita element programmet FEM-Design från Strusoft. Resultaten i rapporten redovisar de maximala dragspänningarna som uppstår i en 15 meter lång vägg utan etappindelning och då gjutning genomförs av genomtänkt etappindelning. Även en variation av friktionsjordens djup analyseras för en utav etappindelningarna. Slutsatsen av resultaten är att gjutetappindelning är en lösning till reduktion av tvång och därmed minskad spänning i betongväggar, då de maximala dragspänningarna reducerades med som högst ca 80%. Effektiviteten av gjutetappindelning är möjlig inom en normal utförandetid.

<p>Void growth and coalescence in a single layer model material with holes were visualized by the environmental electron scanning microscope coupled with in situ tensile test. Single sheet model materials were manufactured with a line of laser drilled holes through thickness. In order to investigate the effect of shear localization, the line of holes were oriented with the misorientation angle <em>θ </em>= 0°, 15°, 30°, and 45°. The α-brass samples were studied to introduce the work hardening effect in comparison with the pure copper samples.</p> <p>By taking images at intervals with small strain increments, the void growth behaviors were visualized during the interrupted tensile testing. The void coalescence (defined consistent with Hosokawa et al (2011), as the point at which the voids stopped shrinking laterally) was successfully captured for the first time in the two dimensional studies. The evolutions of void shape change and void rotation during deformation were also studied quantitatively. The results showed that the higher work hardening behaviors can suppress the void coalescence. It also showed that the effect of local volume fraction dominated the coalescence event rather than the void spacing and shear localization. A comparison of the classic models with the experimental results were also made.</p> / Master of Science in Materials Science and Engineering (MSMSE)

yes / The present paper reports the testing of 12 alkali-activated mortars and a control ordinary portland cement (OPC) mortar. The main aim is to develop cementless binder activated by sodium silicate powder. An alkali quality coefficient combining the amounts of main compositions of source materials and sodium oxide (Na2O) in sodium silicate is proposed to assess the properties of alkali activated mortars, based on the hydration mechanism of alkali-activated pastes. Fly ash (FA) and ground granulated blast-furnace slag (GGBS) were employed as source materials. The ratio of Na2O-to-source material by weight for different mortars ranged between 0.038 and 0.164; as a result, alkali quality coefficient was varied from 0.0025 to 0.0365. Flow loss of fresh mortar, and shrinkage strain, compressive strength and modulus of rupture of hardened mortars were measured. The compressive strength development of alkali activated mortar was also compared with the design equations for OPC concrete specified in ACI 209 and EC 2. Test results clearly showed that the flow loss and compressive strength development of alkali-activated mortar were significantly dependent on the proposed alkali quality coefficient. In particular, a higher rate of compressive strength development achieved at early age for GGBS-based alkali-activated mortar and at long-term age for FA-based alkali-activated mortar. In addition, shrinkage strain and modulus of rupture of alkali-activated mortar were comparable to those of OPC mortar.

The mean variance framework (MV) developed by Markowitz in his groundbreaking paper offers a quantitative and rational approach to portfolio selection. It is well known to market practitioners however that the MV optimal portfolios tend to perform subpar. One of the issues of the MV portfolios is that they require the inverse of a large covariance matrix, which is often ill-conditioned. In this thesis, we develop a new approach to circumvent these issues. We propose an optimisation approach akin to least squares linear regression and compare the performance with an establish method, covariance shrinkage. When tested on a set of 30 futures contracts, we find that the models yield promising results albeit somewhat lower than that of the benchmark. / Mean variance ramverket (MV) framtaget av Markowitz i sin banbrytande artikel möjliggör en kvantitativ och rationell metod för portföljallokering. Det är däremot ett väletablerat faktum bland marknadsaktörer att Markowitz-optimala portföljer tenderar att prestera relativt dåligt. Ett av tillkortakommandena av ramverket är den ofta problemtyngda inverteringen av, den ofta stora, kovariansmatrisen som är illa konditionerad. I denna uppsats föreslår vi en ny metod för att kringgå detta problem. Vi föreslår en optimeringsmetodologi mycket lik minsta kvadratmetoden i linjär regression. Denna metod utvärderas sedan mot en vedertagen metod, kovarianskrympning. När vi utvärderar vår modell på 30 stycken terminskontrakt ser vi lovande resultat men finner en Sharpekvot något lägre än referensportföljens.

Thesis (MBA (Business Management))--Stellenbosch University, 2008. / ENGLISH ABSTRACT: Excessive shrinkage threatens the viability of retailers, especially grocery retailers because they operate on low profit margins. One possibility is for retailers to dismiss employees who are perceived to be responsible for excessive shrinkage, but South African law generally requires that the employer prove individual culpability or poor performance to justify a dismissal. In most cases, retailers are not able to identify the exact causes of shrinkage or those employees who may be responsible for the shrinkage. Pep Stores has developed a novel group dismissal model, using a poor performance process, in terms of which a store's entire staff complement is dismissed on the basis of collective responsibility for failing to avoid excessive shrinkage. The Pep model is attractive to retailers because it overcomes the retailer's inability to produce evidence relating to excessive shrinkage. This Study Project seeks to determine whether collective responsibility for shrinkage may be introduced in owner-managed grocery stores and, if not, whether adaptation of the model or new technology might facilitate its introduction. A further objective is to determine whether the applicability of the Pep model correlates to factors such as the size, activity level and complexity of retail stores. Three barriers to the application of the Pep model in grocery retail stores were identified: firstly, the determination of an "acceptable level of shrinkage" that is reasonably attainable; secondly, the conducting of sufficiently accurate stock takes to support dismissals and, thirdly, the existence or creation of circumstances allowing the implementation of collective responsibility for shrinkage. Grocery retailers have no difficulty in identifying an attainable "acceptable level of shrinkage" or in conducting highly accurate stock takes and stock counts. Circumstances allowing the imposition of collective responsibility for shrinkage were, however, clearly not present. Collective responsibility was precluded by the specialised nature of the employees' tasks and a lack of co-responsibility arising from employees' inability to directly observe each other. However, an adapted Pep model is applicable in grocery retail stores at departmental level if the departments are insulated from fraud or error by receiving clerks and cashiers. This insulation may be achieved by implementing joint receiving procedures that involve each department in receiving departmental stock and an increase in cashier monitoring. The introduction of Radio Frequency Identification Technology will ultimately facilitate the implementation of the Pep model through the enhanced insulation of departments. This enhanced insulation is achieved through the ability to track the movement of individual items in stores and the reduction of receiving and cashier error and fraud as a result of the automation of aspects of these functions. This technology, however, is unlikely to be implemented in the short term given the significant cost of RFID tags and the technical and organisational constraints to adoption. Perceptions on the applicability of the Pep model are correlated in smaller stores to total store floor areas, while the applicability of the model in larger stores is correlated to the size of staff complements. This suggests that the model may be ideally applicable in smaller stores, where the total store floor area is relatively smaller and in larger stores, where the staff complements are relatively larger. / AFRIKAANSE OPSOMMING: Oormatige voorraadverlies bedreig die lewensvatbaarheid van kleinhandelaars, veral kruidenierswarehandelaars, omdat hulle met klein winsmarges werk. Een moontlikheid is dat kleinhandelaars werknemers ontslaan wat gesien word as die verantwoordelikes vir oormatige voorraadverlies, maar die Suid-Afrikaanse reg vereis oor die algemeen dat die werkgewer indiwiduele skuld of swak prestasie bewys om ontslag te regverdig. In die meeste gevalle is kleinhandelaars nie in staat om die presiese oorsake van voorraadverlies, of die werknemers wat vir die voorraadverlies verantwoordelik mag wees, te identifiseer nie. Pep Stores het 'n vindingryke groep-ontslagmodel ontwikkel, met gebruik van 'n swakprestasieproses, ingevolge waarvan 'n winkel se hele personeel ontslaan word op grond van kollektiewe verantwoordelikheid weens versuim om oormatige voorraadverlies te vermy. Die Pep-model is aantreklik vir kleinhandelaars, want dit oorkom die kleinhandelaar se onvermoë om bewys te lewer in verband met oormatige voorraadverlies. Hierdie navorsingsprojek probeer vasstel of kollektiewe verantwoordelikheid vir voorraadverlies ingestel kan word in eienaarbestuurde kruidenierswinkels en, indien nie, of aanpassing van die model, of nuwe tegnologie, die invoer daarvan sou kon fasiliteer. 'n Verdere doelstelling is om vas te stel of die toepaslikheid van die Pepmodel korreleer met faktore soos die grootte, bedrywigheidsvlak en kompleksiteit van kleinhandelwinkels. Drie struikelblokke vir toepassing van die Pep-model in kleinhandelkruidenierswinkels is geidentifiseer: eerstens, die bepaal van 'n "aanvaarbare voorraadverliesvlak" wat redelik haalbaar is; tweedens, die uitvoer van voldoende akkurate voorraadopnames om ontslag te steun en derdens die bestaan of skep van omstandighede wat die implementering van kollektiewe verantwoordelikheid vir voorraadverlies moontlik sal maak. Kruidenierskleinhandelaars ondervind geen probleme met die identifisering van haalbare "aanvaarbare voorraadverliesvlakke" of met die uitvoer van hoogs akkurate voorraadopnames en - tellings nie. Omstandighede wat die oplê van kollektiewe verantwoordelikheid vir voorraadverlies moontlik maak, was egter duidelik nie aanwesig nie. Kllektiewe verantwoordelikheid is uitgesluit weens die gespesialiseerde aard van die werknemers se take en 'n gebrek aan mede-verantwoordelikheid weens werknemers se onvermoë am mekaar direk waar te neem. 'n Aangepaste Pep-model is egter toepasbaar in kruidenierskleinhandelwinkels op departementele vlak indien die departemente van bedrog of foute deur ontvangsklerke en kassiere afgeskerm word. Die afskerming kan bereik word deur die implementering van gesamentlike ontvangsprosedures wat elke departement betrek by die ontvangs van departementele voorraad en verskerpte kassiermonitering. Die invoer van Radiofrekwensie-identifikasietegnologie sal uiteindelik die implementering van die Pep-model fassiliteer deur die verhoogde afskerming van departemente. Hierdie verhoogde afskerming word bereik deur die vermoë om die beweging van indiwiduele items in winkels na te speur en die vermindering van ontvangs- en kassierfoute en -bedrog as gevolg van die outomatisering van aspekte van die funksies. Hierdie tegnologie sal egter waarskynlik nie oor die korttermyn toegepas word nie weens die aansienlike koste van RFIO-etikette en die tegniese en organisatoriese beperkings op die invoer daarvan. Persepsies oor die toepasbaarheid van die Pep-model word in kleiner winkels gekorreleer met die totale winkelvloeroppervlak, terwyl die toepasbaarheid van die model in groter winkels gekorreleer word met die grootte van die personeelkorps. Dit suggereer dat die model ideaal toepasbaar mag wees in kleiner winkels waar die totale winkelvloeroppervlak relatief kleiner is en in groter winkels waar die personeelkorps relatief groter is.

High performance concrete (HPC) provides a long lasting, durable concrete that is typically used in bridge decks due to its low permeability, high abrasion resistance, freeze-thaw resistance and strength. However, this type of concrete is highly susceptible to the deleterious effects of both autogenous and drying shrinkage. Both types of shrinkage occur when water leaves small pores , (< 50 nm) in the paste matrix to aid in hydration or is lost to the surrounding environment. Autogenous deformation (self-desiccation) occurs as the internal relative humidity decreases due to hydration of the cementitious material. Drying (and subsequent shrinkage) occurs when water is lost to the environment and continues until the internal relative humidity is equivalent to the ambient relative humidity. Typically, the magnitude of autogenous shrinkage is less than that of drying shrinkage. These two types of shrinkage do not act independently, and the total shrinkage is the aggregation of the two shrinkage mechanisms. It is imperative to minimize the amount of shrinkage in restrained members, such as bridge decks, to reduce the cracking potential. Various methods have been researched to minimize both types of shrinkage. Two methods to that have been reported to reduce shrinkage were selected for further research; internal curing using pre-soaked lightweight fine aggregate (LWFA) and shrinkage reducing admixtures (SRAs). The purpose of this study was to determine the long-term drying shrinkage performance of these two methods while reducing the external curing duration of 14 days for new bridge deck construction as specified by the Oregon Department of Transportation. In addition to monitoring drying shrinkage, durability testing was performed on concrete specimens to ensure these shrinkage mitigation methods performed at levels similar to concrete with the current mixture design. Freeze-thaw testing, permeability testing and restrained drying shrinkage testing were conducted. It was concluded that the combination of SRAs and pre-soaked LWFA was the most effective method to reduce longterm drying shrinkage for all curing durations (1, 7, and 14 day). Additionally, for durability testing, it was found that the use of SRAs performed the best in freeze-thaw testing, chloride permeability and restrained shrinkage. / Graduation date: 2012

Gelžbetonis yra kompozitinė medžiaga, kurios komponentai yra betonas ir plieninė armatūra. Kaip žinoma, betono stipris tempiant yra 1020 kartų mažesnis nei stipris gniuždant. Atrodytų, kad tempiamojo betono įtaka, atlaikant įrąžas skerspjūvyje, yra nereikšminga. Iš tiesų, nustatant lenkiamųjų elementų stiprumą normaliniame pjūvyje, tempiamo betono įtempių galima nevertinti. Kita vertus, skaičiuojant įlinkius, neįvertinus tempiamojo betono įtakos, gali būti daroma didesnė nei 100 % paklaida. Adekvatus supleišėjusio tempiamojo betono įtakos įvertinimas, nustatant trumpalaike apkrova veikiamų gelžbetoninių elementų deformacijas, yra bene svarbiausia ir sudėtingiausia problema. Plyšio vietoje betonas negali atlaikyti tempimo įtempių, todėl visą įrąžą atlaiko armatūra. Kadangi plyšyje ir gretimuose pjūviuose armatūra praslysta betono atžvilgiu, kontakto zonoje atsiranda tangentiniai įtempiai. Šie įtempiai perduodami betonui, todėl jis atlaiko tempimo įtempius. Armatūros ir betono sąveika ruožuose tarp plyšių standina gelžbetoninį elementą. Supleišėjusio betono gebėjimas atlaikyti tempimo įtempius vadinama tempimo sustandėjimu (angl. tension stiffening). Šis efektas dažniausiai modeliuojamas supleišėjusio betono įtempių ir deformacijų diagrama, taikant vidutinių plyšių koncepciją. Tuomet neatsižvelgiama į diskrečius plyšius, o supleišėjęs betonas traktuojamas kaip ortotropinė medžiaga su pakitusiomis savybėmis. Dauguma tempimo sustandėjimo modelių įvertina betono įtempių... [toliau žr. visą tekstą] / Modelling behaviour of cracked tensile concrete is a complicated issue. Due to bond with reinforcement, the cracked concrete between cracks carries a certain amount of tensile force normal to the cracked plane. Concrete adheres to rein-forcement bars and contributes to overall stiffness of the structure. The phe-nomenon, called tension-stiffening, has significant influence on the results of short-term deformational analysis. Assumption of a tension-stiffening law has great influence on numerical results of load – deflection behaviour of reinforced concrete members subjected to short – term loading. Under wrong assumption of this law, errors in calculated deflections, particularly for lightly members, may exceed 100 %. Most known tension-stiffening relationships relate average stresses to average strains. However, some experimental and theoretical investi-gations have shown that tension-stiffening may be affected by other parameters. The scientific supervisor of the thesis has proposed a tension-stiffening model depending on reinforcement ratio. This model has been developed using experi-mental data reported in the literature. Besides, concrete shrinkage effect was not taken into account. The main objective of this PhD dissertation is to propose a tension-stiffening law for bending RC members subjected to short-term loading with eliminated concrete shrinkage effect.

The effects of pore density and distribution were investigated on the fatigue crack initiation behavior in an A713 sand cast aluminum alloy plate of 12 mm thickness. The applied stress- the number of cycles to failure (S-N) curves of the samples taken from 2 mm and 5 mm from the free surface were obtained using four-point bend fatigue testing at room temperature, frequency of 20 Hz, stress ratio of 0.1, sinusoidal waveform, and in ambient air. The fatigue strengths of both, the 2 mm and 5 mm samples were 60% of the yield strength (σy=171.9 MPa) of the alloy. Optical microscopy, SEM, and EDS mapping were used to characterize pores and particles in 2 mm and 5 mm samples. The average pore sizes of the 2 mm and 5 mm samples were measured to be 10 to 14 μm, and 14 to 32 μm, respectively. The pore number densities in 5 mm and 2 mm samples were comparable, but higher number densities of non-clustered coarse pores (gas pores) were observed in 5 mm samples. The crack population found after fatigue testing showed a Weibull function of stress level. The peaks of strength distributions of fatigue weak link density of 5 mm and 2 mm samples were measured to be 0.017 mm-2 at 67.6 % σy, and 0.01027 mm-2 at 69.5% σy. Crack populations, when normalized by number densities of gas pores (non-clustered) and number densities of shrinkage pores (clustered), giving crack nucleation rate (crack/pore, mm-2), showed a good fit with the Weibull function in 2 mm and 5 mm samples. Shrinkage and gas pores could both become the main crack initiation sites (i.e. fatigue weak links) in this alloy. Higher nucleation rates of gas pores and shrinkage pores were observed in 5 mm samples compared to those rates in 2 mm samples. At high applied stresses, the 2 mm samples showed better fatigue lives than those of 5 mm samples. Fractured surfaces were analyzed using SEM and found that the main crack initiation were predominately from pores. The pores on the fractured surfaces were counted and their depth and width were measured. It was found that the cracks may not necessarily initiate from coarse pores, but sometimes from shrinkage pores (i.e. group of pores). The depth from the free surface, the width, the size, and the orientation of pores are key factors in increasing the driving force for crack initiation and subsequently those pores turn into long cracks. Moreover, the aspect ratios of pores on the main cracks were measured and found that in 5 mm samples, some pores have an aspect ratios of less than 0.7, which means that these pores are elongated in depth and have a narrow width which increase the stress concentration on the surface, thus, increasing the driving force for crack nucleation.

High-dimensional data are becoming increasingly available as data collection technology advances. Over the last decade, significant developments have been taking place in high-dimensional data analysis, driven primarily by a wide range of applications in many fields such as genomics, signal processing, and environmental studies. Statistical techniques such as dimension reduction and variable selection play important roles in high dimensional data analysis. Sufficient dimension reduction provides a way to find the reduced space of the original space without a parametric model. This method has been widely applied in many scientific fields such as genetics, brain imaging analysis, econometrics, environmental sciences, etc. in recent years. In this dissertation, we worked on three projects. The first one combines local modal regression and Minimum Average Variance Estimation (MAVE) to introduce a robust dimension reduction approach. In addition to being robust to outliers or heavy-tailed distribution, our proposed method has the same convergence rate as the original MAVE. Furthermore, we combine local modal base MAVE with a $L_1$ penalty to select informative covariates in a regression setting. This new approach can exhaustively estimate directions in the regression mean function and select informative covariates simultaneously, while being robust to the existence of possible outliers in the dependent variable. The second project develops sparse adaptive MAVE (saMAVE). SaMAVE has advantages over adaptive LASSO because it extends adaptive LASSO to multi-dimensional and nonlinear settings, without any model assumption, and has advantages over sparse inverse dimension reduction methods in that it does not require any particular probability distribution on \textbf{X}. In addition, saMAVE can exhaustively estimate the dimensions in the conditional mean function. The third project extends the envelope method to multivariate spatial data. The envelope technique is a new version of the classical multivariate linear model. The estimator from envelope asymptotically has less variation compare to the Maximum Likelihood Estimator (MLE). The current envelope methodology is for independent observations. While the assumption of independence is convenient, this does not address the additional complication associated with a spatial correlation. This work extends the idea of the envelope method to cases where independence is an unreasonable assumption, specifically multivariate data from spatially correlated process. This novel approach provides estimates for the parameters of interest with smaller variance compared to maximum likelihood estimator while still being able to capture the spatial structure in the data.