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Columns with three spans separated by elastic braces are analyzed. The influences of translational and rotational resistance at the braces, various end conditions, and the bracing locations for the perfect columns with equal and unequal spans subjected to uniform and nonuniform axial load are investigated. For imperfect columns with equal or unequal spans subjected to uniform compression, the effects of various end conditions at the top and various initial deflections are studied. "Ideal stiffness" and "full bracing" only exist for these columns with equal spans and translational restraints with identical spring stiffness at the braces. Rotational restraints at the braces or at the ends improve the load-carrying capacity of the column. For the imperfect column, three types of initial deflection on the columns with equal and unequal spans and various end conditions at the top are analyzed. Based on a linear elastic analysis, the bracing force induced by a cubic initial deflection for a three-span column often exceeds 20/0 of the axial load. The violation of this rule of thumb in practice is readily revealed. Design curves for the effect of the bracing stiffness on the deflection ratio and bracing force percentage are created for the determination of bracing requirements. / Master of Science

Vita. / Digitized by Kansas Correctional Industries

By using a nonlinear computer analysis, a parametric study is developed in order to examine the accuracy of the Moment Magnifier Method of the American Concrete Institute Code (ACI 318-83). The variables used in the parametric study are: axial load intensity, P/Po; column reinforcement ratio, rho; slenderness ratio, klu; shape of column cross section, flexural stiffness ratio, and distribution of axial loads. In the parametric study, 216 cases of single bay fixed-base portal frames are examined. The higher moment for each one of these frames at failure are then compared with the design moment predicted by the Moment Magnifier Method of the American Concrete Institute Code (ACI 318-83). The Moment Magnifier Method proved to be very conservative when the columns are subjected to high level of axial loads and when the slenderness ratio is increased.

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: Supercritical fluids are enjoying ever increasing popularity as a solvent medium for extraction, stripping and absorption processes. Being readily tuneable and able to achieve sharp, highly efficient separations, supercritical fluids present an attractive alternative to traditional solvents, while using less intrinsically harmful compounds. Although the potential of supercritical fluids as solvents have been known for more than a century, there are still several areas of uncertainty, one being the hydrodynamics of extraction columns operating under supercritical conditions. This shortcoming can be attributed to the satisfactory performance of modified standard hydrodynamics to approximate column design, along with a predominant culture of overdesign in process engineering. Even though modified subcritical hydrodynamic models provide a good approximation they do not successfully predict the effect of changes in density, viscosity and surface tension of a supercritical fluid, leading to inaccuracies in column design. This study investigates the state of hydrodynamics under supercritical conditions in counter current packed columns discussed in literature, identifies shortcomings in existing literature and devises a way of addressing the said shortcomings. The primary objective of this study is to establish a multipurpose supercritical pilot plant capable of measuring hydrodynamics under supercritical conditions, followed by the secondary objective of measuring preliminary hydrodynamic data to prove the plant can deliver on its design requirements in measuring reliable hydrodynamic data. During a survey of available literature it was found that very little experimental work has been performed on hydrodynamics under supercritical conditions and especially on random packings. Further it is found that the systems investigated in literature were conducted under conditions of significant mass transfer. As mass transfer directly affects flow rates and fluid properties of the fluids in the column, it is vital to use systems with very little to no mass transfer. This ensures the most accurate approach possible when investigating fundamental hydrodynamic behaviour. Finally it was found that there are no well-defined correlations available for a wide range of packings, fluid properties and hydrodynamic phenomena for columns under supercritical conditions. To remedy the shortcomings in hydrodynamic data it was decided that more pilot plant work is required. It was found that no pilot plants available can measure hydrodynamic data. An investigation was performed into retrofitting available pilot plants, plants used by other research groups and commercially available plants. It was concluded that the best option was to salvage the major parts of an existing old pilot plant and use them to construct a new, customized pilot plant. This provides the opportunity of constructing a custom, multipurpose pilot plant capable of use in future research. After an initial concept design a full design of the new pilot plant was performed. The plant consists of two columns of 17 mm and 38 mm inside diameter and 3.5 m and 1.5 m packed height, respectively, and is capable of pressures and temperatures of up to 300 bar and 200°C. Furthermore the pilot plant can measure liquid hold-up, pressure drop, flooding and entrainment in accordance with the objective of measuring supercritical hydrodynamic data. Liquid hold-up was determined by stopping the process and allowing the column to drain, after which the volume drained was measured. To measure the pressure drop an Endress+Hauser Deltabar S PMD75 DP cell was used. Flooding was determined using the measured pressure drop and volumetric rate of column overheads, from where a hydrodynamically inoperable state is defined. Overall entrainment, although unlikely due to the presence of a demister in the column, was investigated by comparing the column overheads to literature phase equilibria. Preliminary hydrodynamic testing was performed using the 38mm diameter column packed with 1/4” Dixon rings. Testing is performed with at 120 bar and 40°C with a CO2 supercritical phase and polyethylene glycol liquid phase with an average molar mass of 400 (PEG 400). The hydrodynamic data gathered showed expected trends, but showed discrepancy with literature due to differences in liquids used, column packing and experimental system between the respective studies. / AFRIKAANSE OPSOMMING: Superkritiese vloeistowwe is besig om toenemende gewildheid as 'n oplosmiddel vir ekstraksie, stroping en absorpsie prosesse te geniet. Hierdie gewildheid is as gevolg van ʼn vermoë om skerp, hoogs effektiewe skeidings te bewerkstellig deur gebruik te maak van ʼn maklik aanpasbare oplosmiddel wat minder intrinsiek skadelik is as tradisionele oplosmiddels. Hierdie voordele lei daartoe dat superkritiese vloeiers as ʼn aantreklike alternatief tot tradisionele oplosmiddels gesien kan word. Alhoewel die potensiaal van superkritiese vloeistowwe as oplosmiddels al vir meer as ʼn eeu bekend is, is nog weinig eksperimentele werk al gedoen oor die hidrodinamiese gedrag van superkritiese gepakte kolomme. Hierdie tekortkoming kan toegeskryf word tot die bevredigende prestasie van aangepaste standaard hidrodinamiese korrelasies gedurende superkritiese kolomontwerp en ʼn oorheersende kultuur van oorontwerp in proses-ingenieurswese. Alhoewel aangepaste standaard hidrodinamiese korrelasies ʼn aanvaarbare benadering bied, beeld dit nie die effek van die veranderde digtheid, viskositeit en oppervlakspanning van ʼn superkritiese vloeistof uit nie, wat lei tot foute in kolomontwerp. Hierdie studie ondersoek die stand van superkritiese hidrodinamika in literatuur, spesifiek in teenstroom gepakte kolomme. Tekortkominge in die bestaande literatuur is geïdentifiseer en 'n metode om die genoemde tekortkominge reg te stel is bedink. Die primêre doel van hierdie studie is om 'n veeldoelige superkritiese loodsaanleg te bou wat tot staat is om superkritiese hidrodinamika te meet, gevolg deur die sekondêre doelwit wat die meet van voorlopige hidrodinamiese data behels, wat sal bewys dat die loodsaanleg voldoen aan ontwerpsvereistes. Tydens 'n opname van beskikbare literatuur was daar gevind dat weinig eksperimentele werk al gedoen is in die veld van superkritiese hidrodinamika, en nog minder oor sogenoemde ongeordende of ‘random’ kolompakkings. Verder is daar gevind dat eksperimente uitgevoer in literatuur slegs bestaan uit stelsels waar beduidende massa-oordrag plaasvind. Aangesien massa-oordrag die vloeitempo en fisiese eienskappe van die vloeiers in ʼn kolom direk beïnvloed, is dit noodsaaklik om gebruik te maak van stelsels met baie min of geen massaoordrag. Dit verseker ʼn akkurate benadering tot die meet van fundamentele hidrodinamiese gedrag. Laastens is gevind dat daar geen hidrodinamiese korrelasies beskikbaar is wat ʼn wye verskeidenheid van kolompakkings, vloeier eienskappe en hidrodinamiese verskynsels onder superkritiese toestande dek nie. Om die tekortkominge in superkritiese hidrodinamika in literatuur aan te spreek, word meer eksperimentele loodsaanlegwerk vereis. Daar is gevind dat geen van die beskikbare loodsaanlegte hidrodinamiese data kan meet nie. Ondersoek is ingestel tot die ombouing van bestaande loodsaanlegte, aanlegte wat gebruik is deur ander navorsingsgroepe en kommersieel beskikbare aanlegte. Daar is tot die gevolgtrekking gekom dat die beste opsie is om ʼn nuwe loodsaanleg self te bou en gebruik te maak van parte uit een van die ou bestaande aanlegte om kostes laag te hou. Sodoende kan ʼn veeldoelige, pasgemaakte loodsaanleg gebou word wat ook vir toekomstige navorsing gebruik kan word. Na ʼn aanvanklike konsep ontwerp vir die nuwe loodsaanleg, is ʼn volledige ontwerp gedoen. Die aanleg bestaan uit twee kolomme van onderskeidelik 17 mm en 38 mm binnedeursnee en 3,5 m en 1,5 m gepakte hoogte, en is in staat om eksperimente by ʼn maksimum druk en temperatuur van tot 300 bar en 200°C uit te voer. Verder is die loodsaanleg in staat daartoe hidrodinamiese data te meet, naamlik die vloeistofophoud in die kolom, drukval oor die kolompakking, kolomvloed en druppel meesleuring. Die vloeistofophoud in die kolom is bepaal deur alle voer tot die kolom te stop en tyd toe te laat vir die vloeistof om te dreineer, waarna die gedreineerde afgetap en gemeet is. Om die drukval te meet word ʼn Endress+Hauser Deltabar S PMD75 DP sel gebruik. Kolomvloed is bepaal met behulp van die drukval oor die kolom en die vloeitempo van die kolom se boonste produkstroom, van waar ʼn hidrodinamies onbruikbare toestand gedefinieer word. Algehele druppel meesleuring, alhoewel onwaarskynlik as gevolg van die teenwoordigheid ʼn ontwasemer in die kolom, is wel ondersoek deur die vloeistofinhoud in die kolom se boonste produkstroom te vergelyk met fase ewewigsdata in literatuur. Voorlopige hidrodinamiese eksperimente is uitgevoer met behulp van die 38mm deursnee kolom gepak met 1/4 " Dixon ringe. Eksperimente is uitgevoer by 120 bar en 40 ° C met 'n CO2 kritiese fase en 'n poliëtileenglikol vloeistof fase met ʼn gemiddelde molêre massa van 400 (PEG 400). Die hidrodinamiese data het verwagte tendense getoon, maar diskrepansies met literatuur waardes. Die verskille tussen die eksperimentele en literatuur data word geregverdig deur die verskille tussen die vloeistowwe, pakking en eksperimentele stelsels wat in die onderskeie studies gebruik is.

Microreproduction of original thesis. / Thesis (PhD)--Stellenbosch University, 1990. / Some digitised pages may appear illegible due to the condition of the original microfiche copy. / ENGLISH ABSTRACT: see item for full text / AFRIKAANSE OPSOMMING: sien item vir volteks.

Problem definition and purpose: In 2015, the newspapers sports columns is filled with opinions and analyzes of the events foretold by self-proclaimed experts, sports journalists at the newspapers, This is done to market themselves and their employer, create a relationship with their readers and stand out from the competition. In this thesis we researched two Swedish tabloids, to try to establish whether there has been a notable change in opinions on the sports sections during the last twenty years. Method and material: Quantative content analysis of sport pages of Swedish tabloids Aftonbladet and Expressen during 4-10 November 1995, 2005 and 2015. By identifying how many of the published articles that can be categorized as opinions, and by measuring those articles in square centimeter, we are using graphs and tables to show how the opinion-based material has changed fron 1995 until 2015. Main result: The thesis shows an increasing in opinions and opinion based journalism in Swedish tabloids sport pages over the course of a twenty-year period.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Concrete filled double skin tube (CFDST) columns is a new method of column construction. CFDST columns consists of two steel hollow sections, one inside the other, concentrically aligned. The cross-sections of the two hollow sections does not have to be the same shape. Concrete is cast in between the two hollow sections resulting in a CFDST. This study only considers CFDST columns constructed with circular steel hollow sections. The advantages of CFDST construction include: ● The inner and outer steel hollow sections replaces the traditional steel reinforcement that would be used in a normal reinforced concrete column. This reduces the construction time since there is no need to construct a reinforcing cage. ● The steel hollow sections acts as a stay in place formwork, eliminating the need for traditional formwork. This also reduces construction time. ● The steel hollow sections confine the concrete, making it more ductile and increasing its yield strength. The objective of this study is to identify methods that can predict the axial capacity of eccentrically loaded circular CFDST columns. Methods chosen for the investigation are: 1. Finite element model (FEM). A model was developed to predict the behaviour of eccentrically loaded CFDST columns. The FE model uses a concrete material model proposed in literature for stub columns. The aim was to determine whether the material model is suited for this application. 2. The failure load of CFDST columns under concentric loading was calculated using a model obtained in literature. These capacities were compared to the experimental test results of eccentrically loaded CFDST columns to establish a correlation. This study found that the concrete material model used does not adequately capture the behaviour resulting in the axial response of the column being too stiff. The difference between the eccentrically loaded experimental test results and the calculated concentrically loaded capacity showed a clear trend that could be used to predict the capacity of eccentrically loaded CFDST columns. / AFRIKAANSE OPSOMMING: Beton-gevulde dubbel laag pyp (BGDLP) kolomme is ‘n nuwe metode van kolom konstruksie. BGDLP kolomme bestaan uit twee staal pyp snitte, die een binne die ander geplaas met hul middelpunte opgelyn, die dwarssnit van die twee pype hoef nie dieselfde vorm te wees nie. Beton word dan in die wand tussen die twee pyp snitte gegiet. Die resultaat is ‘n hol beton snit. Hierdie studie handel slegs oor BGDLP kolomme wat met ronde pyp snitte verwaardig is. Die volgende voordele kan aan BGDLP toegeken word: ● Die binne en buite staalpype vervang die tradisionele staal bewapening was in normale bewapende-beton gebruik sou word. Dus verminder dit die tyd wat dit sal neem om die kolom op te rig. ● Die staalpypsnitte is ook permanente vormwerk. Dit doen dus weg met die gebruik van normale bekisting, wat ook konstruksie tyd spaar. ● Die buite-staalpypsnit bekamp die uitsetting van die beton onder las. Hierdie bekamping veroorsaak dat die beton se gedrag meer daktiel is en ‘n hoër falings spanning kan bereik. Die doel van die studie is om metodes te identifiseer wat gebruik kan word om die aksiale kapasiteit onder eksentriese laste van BGDLP kolomme te bepaal. Twee metodes was gekies: 1. Eindige element model. ‘n Model was ontwikkel om die gedrag van BGDLP kolomme te voorspel. Die mikpunt was om te bepaal of ‘n beton materiaal gedrag model vanuit die literatuur gebruik kan word om BGDLP kolomme te modelleer. 2. Die swiglas van BGDLP kolomme onder konsentriese belasting was bereken vanaf vergelykings uit die literatuur. Hierdie swiglaste was vergelyk met die eksperimentele toets resultate vir eksentriese belaste BGDLP kolomme om ‘n korrelasie te vind. Hierdie studie het bewys dat die beton materiaal model uit die literatuur kan nie gebruik word om die swiglaste van BGDLP kolomme te bepaal nie. Die model het die gedrag te styf gemodelleer. Die verskil tussen die berekende konsentriese belaste swiglas en die eksperimentele resultate van eksentriese BGDLP kolomme was voorspelbaar en kan gebruik word om die swiglas van eksentriese belaste BGDLP kolomme te voorspel.

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy