To see the other types of publications on this topic, follow the link: Columns.
Dissertations / Theses on the topic 'Columns'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Columns.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Jemah, Adel Karem. "Buckling of stayed columns and elastically supported columns." Thesis, Cardiff University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278598.
Full text
2
Hazel, William Andrew. "Fourteen Columns." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/44950.
Full textAbstract:
The thesis inquiry is a study of the interrelations between character, emotion and rationality in architecture. The primary modes of representation are digital still photography and hand drawing. To best illuminate these issues the work of the eye and hand of the architect play a vital role. Pastel, pencil and charcoal are the preferred media for the works on paper. Programmatically the building is a boathouse for eight-men crew shells.
The boathouse is embedded into an ideal hillside, with one curved side angled slightly to the water and the landscape beyond. Together with a generous curved roof running the length of the boathouse they provide a covered architectural prow and dry sanctuary below for the storage of the crew shells. From the prow above one has an expansive overlook on the water and the varied activities upon it.
In the thesis project water is not seen as a substance, but rather as a material with a capacity to influence the character of the interior space. For example in the lower level of the boathouse there are small windows adjacent to an artificial water basin. Filtered sunlight passes through the water collected in the basin and then through the small windows. This condition allows a subtle colored light to pervade the lower space.
Another important aspect of this building is a consideration of the twenty-four hour rhythm of day and night. For much of the rowing community, mornings and afternoons are when races or practice activities occur. However the building must be able to show itself when the sun is arriving and departing. In the morning the boathouse and its interior act as an invitation to the rising sun. At night the building provides light to gently
illuminate the darkening surroundings at dusk â similar to a lighthouse resting on its side for shells to navigate towards.Master of Architecture
3
Jovanovic, Dejan, and Ruslan Khalilov. "Transverse force absorption in column base mounts for steel columns : Screw joints in column bases." Thesis, KTH, Byggteknik och design, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-302520.
Full textAbstract:
It is common to use different construction materials in combination such as concrete, steel, wood and glass in order to optimize buildings. The purpose of this is to reduce weight and increase load capacity, but it also facilitates assembly and reduces construction time. Steel column bases anchored in concrete foundations are an example of a combination of interaction nodes between steel and concrete elements. This report studies the friction between the lower edge of the base plate and the grout, which is a function of the normal force of the column. The friction that occurs between the square washer and the foot plate has also been examined as a result of the tightening moment. The work has placed great focus on discussing the advantages and disadvantages of the different methods for transverse force absorption in column bases. Delimitations have been made, the attachment of the column to the base plate has not been taken into account in this report, as this depends on which column cross section is selected and must be checked for the specific case. To arrive at the results, an in-depth literature study was conducted to gather information on the various issues and a calculation model in Excel was created. The calculation model was used to check how large the design load-bearing capacity is for transverse force absorption in a column base, but the checks were only made for non-prestressed joints. This is because prestressed joints also have other factors that affect the transverse resistance, outside the purpose and issue of the work. The Excel model is based on producing the results from calculation with nominal clamping force and comparing it with clamping force calculated with tightening torque. The results will be reported in the form of graphs and tables, where it will be possible to read the difference in the dimensioning load-bearing capacity for transverse force absorption in non-prestressed joints at nominal clamping force and clamping force calculated with tightening torque. The report shows a clear difference in results, where the nominal clamping force became significantly larger and this is supported by handbook on screw joints, as it is mentioned that “it is not possible to give an exact value of the coefficient of friction due to the large number of factors that affect ”, this means that the impact on the clamping force will be large.Det är vanligt förekommande att man använder sig av olika konstruktionsmaterial i kombination med varandra såsom betong, stål, trä och glas för att på så sätt kunna optimera byggnader. Syftet med detta är att minska vikt och öka belastningskapacitet, men det underlättar även montaget och minskar byggtiden. Pelarfötter av stål förankrade i betongfundament är ett exempel på en kombination av samverkansknutpunkter mellan stål och betongelement. I denna rapport studeras friktionen mellan underkant fotplatta och undergjutning, som är en funktion av pelarens normalkraft. Även friktionen som uppstår mellan fyrkantsbrickan och fotplattan kommer att undersökas som ett resultat av åtdragningsmomentet. Arbetet har lagt stor fokus på att diskutera för- och nackdelar med de olika metoderna för tvärkraftsupptagning i pelarfötter. Avgränsningar har gjorts, pelarens infästning till fotplåten har inte beaktats i denna rapport, eftersom detta är beroende av vilket pelartvärsnitt som är valt och måste kontrolleras för det specifika fallet. För att komma fram till resultaten utfördes en fördjupad litteraturstudie för att samla ihop information om de olika frågeställningarna och en beräkningsmodell i Excel skapades. Beräkningsmodellen användes för att kontrollera hur stor den dimensionerande bärförmågan är för tvärkraftsupptagning i en pelarfot, men kontrollerna görs endast för icke förspända förband. Detta eftersom förspända förband även har andra faktorer som påverkar tvärkraftskapaciteten, utanför arbetets syfte och frågeställning. Excel-modellen går ut på att ta fram resultaten ur beräkning med nominell spännkraft och jämföra den med spännkraft beräknad med åtdragningsmoment. Resultaten redovisas i form av grafer och tabeller, där man kan läsa av skillnaden i den dimensionerande bärförmågan för tvärkraftupptagning i icke förspända förband vid nominell spännkraft och spännkraft beräknad med åtdragningsmoment. Rapporten visar en tydlig skillnad i resultat, där den nominella spännkraften blev betydligt större och detta stöds av handbok om skruvförband, då det nämns att “det är inte möjligt att ge ett exakt värde på friktionskoefficienten på grund av det stora antalet faktorer som påverkar”, detta medför att inverkan på klämkraften blir stor.
4
Lau, Hieng Ho. "The influence of column base connectivity on the stability of columns and frames." Thesis, Oxford Brookes University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394626.
Full text
5
Malkin, Douglas Scott, and Douglas Scott Malkin. "An Investigation of a Novel Monolithic Chromatography Column, Silica Colloidal Crystal Packed Columns." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/193936.
Full textAbstract:
Many researchers have investigated ways to improve the separation power of conventional chromatography, most notable is the development of ultra-high performance liquid chromatography (UHPLC). However, only slight improvements in separation efficiency have been achieved up to this point, and unfortunately, modern reversed phase liquid chromatography (RPLC) methods do not have high enough resolving power to analyze complex proteomic mixtures.Uniformly sized silica particles from 10 nm to 1 micron are known to self-assemble into a highly ordered face centered cubic crystal. Silica colloidal crystals have shown recent promise in biological applications such as permselective nanoporous membranes, DNA sieving, reversed phase separation of small molecules on planar substrates, protein sieving, microarrays, total internal reflection fluorescence microscopy of live cells, and 3-D scaffolds for supported lipid films. In this work, silica colloidal crystals packed in capillaries are explored for their potential improvement in the efficiency of reversed phase chromatography.The silica colloidal crystal columns were chemically stabilized by with trichlorosilanes. The trichlorosilanes form chemical bonds between the particles and the particles and the substrate creating an increase in mechanical stability, and at the same time, providing an excellent chromatographic monolayer. After stabilization the fritless columns were able to withstand the pressure limit of the commercial UHPLC. Next, the columns were characterized using a small dye molecule, 1,1' - Didodecyl - 3,3,3',3' - tetramethylindocarbocyanine (DiIC12). The dye was run under capillary electrochromatography (CEC), and sub-micron plate heights were achieved. Further, a van Deemter plot of the dye molecule indicates that the plate height is largely due to the molecule's diffusion. This result suggests that the plate heights for proteins would be even smaller, since proteins have diffusion coefficients an order of magnitude smaller. The analysis of proteins by CEC yielded nanometer plate heights. Finally, pressure driven flow separations coupled with nano-electrospray ionization (n-ESI) MS have also been explored. The Poiseuille flow profile has been shown not to perturb the low plate heights. Gradient elution of peptides was also achieved, and the results demonstrate the highest chromatographic peak capacities for short analysis times to date.
6
Vais, Anca Mihaela. "Side reboiled distillation columns." Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270237.
Full text
7
Khalil, Nariman Jaber. "Slender reinforced concrete columns." Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305374.
Full text
8
BUFFONI, SALETE SOUZA DE OLIVEIRA. "PARAMETRIC INSTABILITY OF COLUMNS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1998. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=2132@1.
Full textAbstract:
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORUNIVERSIDADE FEDERAL DO PARÁ
O presente trabalho tem por objetivo desenvolver uma formulação e certas estratégias que permitam a análise da perda de estabilidade de colunas esbeltas submetidas a carregamento axial periódico, fenômeno este conhecido como ressonância paramétrica. Uma excitação é dita paramétrica quando aparece nas equações de movimento do sistema na forma de coeficientes variáveis com o tempo - geralmente periódicos - e não como uma não homogeneidade. A coluna é descrita pela formulação clássica de Navier. O presente trabalho trata a coluna considerando-se um e três graus de liberdade com ou sem não-linearidades. As equações de movimento são obtidas utilizando-se o princípio de Hamilton através do método de Ritz. A equação linear (equação de Mathieu) e a equação de Duffing com pequeno amortecimento, são resolvidas de forma aproximada pelo método das múltiplas escalas, revelando a possibilidade de instabilização da posição de equilíbrio em diversas regiões do espaço definido pelos parâmetros de controle. A mesma conclusão é mostrada utilizando-se procedimentos computacionais para a resolução dos sistemas de equações lineares e nãolineares, com ou sem imperfeição geométrica inicial, podendo-se obter assim, a resposta do sistema, planos fase, seções de Poincaré e diagramas de bifurcação. Mostra-se a partir dos resultados numéricos, que a coluna submetida a cargas axiais harmônicas, pode tanto apresentar soluções com o mesmo período da força excitadora, quanto oscilações subarmônicas e superarmônicas de diversas ordens, além de movimentos caóticos.
The main aim of the present work is to develop a formulation and some strategies for the instability analysis of slender columns under an axial harmonic force this phenomenon is known as parametric ressonance. An excitation is said to be parametric if it appears as timedependent - often periodic - coefficients in the equations governing the motion of the system,and not as an inhomogeneous term.The column is described by Navier classical formulation. The present work consider the column with one or three degrees of freedom with or without nonlinearities. The equations governing the motion are obtained by the Ritz method.The linear equation (Mathieu equation) and the Duffing equation with small damping are solved in an approximate way using multiple scales techniques, revealing the possibility of destabilizing the static equilibrium position in certain regions of the control space. A similar conclusion is obtained by employing numerical methods for the solution of linear and nonlinear equation systems with or without initial geometrical imperfections.This enables one to obtain time response, phase space, projections Poincaré sections and bifurcation diagrams. These numerical results show that the column with nonlinearities and loaded by a periodic longitudinal force can present various solutions with the same period as the forcing and subharmonic e superharmonic oscillations, as well as chaotic motions.
9
Lui, Wing Man. "Design of cold-formed high strength stainless steel tubular columns and beam-columns /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202004%20LUI.
Full textAbstract:
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 149-154). Also available in electronic version. Access restricted to campus users.
10
Perea, Tiziano. "Analytical and experimental study on slender concrete-filled steel tube columns and beam-columns." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37303.
Full textAbstract:
The use of composite steel-concrete columns and beam-columns in many structural systems is increasing globally due to the intrinsic synergy when these materials are designed and detailed together properly. However, limited test data are available to justify the structural system response factors and comprehensive design equations in current design specifications. This research, through the testing of 18 full-scale, slender concrete-filled steel tube (CFT) beam-columns, attempts to address the latter need. The circular and rectangular CFT specimens tested for this research are by far the longest and the most slender full-scale CFT members tested worldwide. These CFT specimens were subjected to a complex load protocol that includes pure compression, uniaxial and biaxial bending combined with compression, pure torsion, and torsion combined with compression. In addition, data from the hydrostatic pressure on the steel tubes due to the fresh concrete at casting was evaluated. The single most important contribution of this research is the clarification of the interaction between strength and stability in slender composite concrete-filled columns and beam-columns. Parallel to the experimental study, advanced computational analyses were carried out to calibrate material and element models that characterize the salient features of the observed CFT response, such as steel local buckling and residual stresses, concrete confinement, stability effects, strength, and stiffness degradation, among others. Based on the observed behavior, simplified guidelines for the computation of the strength and stiffness parameters for CFT columns and beam-columns are proposed for design purposes.
11
Trezona, James Richard. "Analysis and design of circular reinforced concrete columns and concrete filled steel tube columns /." Title page, contents and abstract only, 1995. http://web4.library.adelaide.edu.au/theses/09ENS/09enst818.pdf.
Full text
12
Al-Shihri, Marai Abdullah 1958. "BUCKLING STRENGTH OF HEAVY STEEL COLUMNS (WELDED SHAPES, INITIAL CURVED COLUMNS, HOT-ROLLED SHAPES)." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/291869.
Full text
13
Schaller, Markus. "Numerically Optimized Diabatic Distillation Columns." Doctoral thesis, Universitätsbibliothek Chemnitz, 2007. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200701134.
Full textAbstract:
Im Gegensatz zur konventionellen adiabatischen Destillation erfolgt bei der diabatischen Destillation Wärmeaustausch nicht nur am Kondensator und Verdampfer, sondern auch innerhalb der Kolonne an den einzelnen Siebböden, was die Entropieproduktion (=Exergieverlust) des Destillationsprozesses stark reduziert. In dieser Arbeit werden Modellsysteme zur diabatischen Destillation von idealen binären Gemischen mittels numerischer Optimierung untersucht. Das Ausgangsmodell beschränkt sich auf die Minimierung der Entropieproduktion verursacht durch Wärme- und Massentransport im Inneren der diabatischen Destillationskolonne. Im zweiten Modell wird das diabatische Modell um die Irreversibilität bedingt durch den Wärmeaustausch mit der Umgebung erweitert. Im dritten Modellsystem wird anstelle der bis dahin voneinander unabhängig geregelten Bodentemperaturen eine diabatische Implementierung mit seriellen Wärmetauschern untersucht, die nur mehr vier Kontrollvariablen besitzt und besonders zur praktischen Anwendung geeignet ist. Für alle diabatischen Modelle werden die minimale Entropieproduktion und optimalen Betriebsprofile numerisch ermittelt, und mit konventionellen Destillationskolonnen verglichen. Alle Ergebnisse zeigen eine deutlich Reduktion der Entropieproduktion für den diabatische Fall, besonders bei Kolonnen mit vielen BödenContrary to conventional adiabatic distillation, in diabatic distillation columns heat transfer not only happens at the condenser and reboiler but also at the intermediate trays which strongly reduces the entropy production (= exergy losses). In this work, model systems for the diabatic distillation of ideal binary mixtures are investigated numerically.The first model is restricted to the minimization of the entropy production due to heat and mass transfer inside the diabatic column. In the second approach the model is extended with the irreversibility due to heat transfer with the column's surroundings. Instead of independently controlled tray temperatures as in the latter models, we focus on a specific diabatic implementation with sequential heat exchangers, which has merely four controls and which is particularly suitable for practical application. For all diabatic models the minimum entropy production and resulting optimal operating profiles are determined numerically, and compared to the ones obtained for a conventional column. All results show an enormous reduction of the entropy production for the diabatic case, especially for columns with many trays
14
Kim, Dong Keon. "A Database for Composite Columns." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7126.
Full textAbstract:
A database of composite column tests was augmented and utilized to evaluate the proposed AISC 2005 provisions. The database consists of column and beam-column steel-concrete columns (or encased, SRC), circular concrete filled tubes (CCFT), and rectangular concrete filled tube (RCFT). Information on material and geometric properties on each specimen was summarized. The database includes 119 SRC columns, 136 SRC beam-columns, 312 circular CFT columns, 198 circular CFT beam-columns, 222 rectangular CFT columns and 194 rectangular CFT beam-columns. The database has a total of 1181 specimens, an addition of 451 specimens over those in the original database (Aho 1996).
The data on each specimen was analyzed and compared with current design provision for composite columns (AISC 1999 and Eurocode 4), and reassessed by the upcoming 2005 AISC specification. The data indicates that the Eurocode gives good predictions for columns and the AISC 2005 method performs very well for beam-columns. For rectangular CFT columns, all three methods predict the ultimate capacity very well. The main improvement for the AISC 2005 method is its ability to handle specimens which have high yield stress and/or high strength concrete.
15
Flores, Tlacuahuac Antonio. "Robust control of distillation columns." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/8016.
Full text
16
Elmahdy, Ghada. "Buckling of built-up columns." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ30272.pdf.
Full text
17
Xu, Manqiu. "Sparger study in flotation columns." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=64062.
Full text
18
Hunaiti, Y. M. "Behaviour of battened composite columns." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374803.
Full text
19
Philip, J. "Viscous liquids in bubble columns." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235274.
Full textAbstract:
This dissertation is concerned with studies of highly viscous Newtonian and non-Newtonian liquids in bubble columns with, and without, draft tubes. The importance of the parameters influencing bubble column reactors is discussed with reference to previous work. The shapes and rise velocities of single bubbles in these liquids were studied in an 8.8cm diameter column, and the gas holdup, resulting from continuous bubbling of gas into this column, was also measured. Agreement between holdup predicted by the equation of Nicklin et al (1962), and experimental data in die present work and that of other workers is good. The limiting result of Dumitrescu (1943) was found to apply for fully developed slug flow in viscous non-Newtonian liquids in large columns. Gas holdup, in a 15cm diameter bubble column with a draft tube, consisted of large bubbles (slugs), which rapidly rose through the liquid, and very small bubbles, which accumulated in the liquid. These small bubbles were generated near the gas distributor and also at the liquid surface; less than 1% of the total gas flowrate into the system was converted into small bubbles for a highly viscous Newtonian liquid. The gas holdup due to small bubbles in non-Newtonian liquids was much less than that in Newtonian liquids. Large bubble velocities deduced from the bubble column measurements were consistent with the single bubble measurements. Liquid velocities in the 15cm column were measured by a neutrally buoyant flow follower; the liquid circulation rate was found to decrease with an increase in liquid viscosity. A model to predict the liquid circulation rate is outlined. The effect of scale-up on the gas holdup and liquid circulation rate was also studied experimentally in a 60cm square bubble column with a 30cm square draft tube. The bubble size distribution in this column was similar to the 15cm column but liquid velocities were higher, and gas holdup was smaller in the 60cm column.
20
Al-Dunainawi, Yousif Khalaf Yousif. "Intelligent Control for distillation columns." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/15597.
Full textAbstract:
Nowadays, industrial processes are having to be rapidly developed to meet high standards regarding increases in the production rate and/or improving product quality. Fulfilling these requirements is having to work in tandem with the pressure to reduce energy consumption due to global environmental regulations. Consequently, most industrial processes critically rely on automatic control, which can provide efficient solutions to meet such challenges and prerequisites. For this thesis, an intelligent system design has been investigated for controlling the distillation process, which is characterised by highly nonlinear and dynamic behaviour. These features raise very challenging tasks for control systems designers. Fuzzy logic and artificial neural networks (ANNs) are the main methods used in this study to design different controllers, namely: PI- PD- and PID-like fuzzy controllers, ANN-based NARMAL2 in addition to a conventional PID controller for comparison purposes. Genetic algorithm (GA) and particle swarm optimisation (PSO) have also been utilised to tune fuzzy controllers by finding the best set of scaling factors. Finally, an intelligent controller is proposed, called ANFIS-based NARMA-L2, which uses ANFIS as an approximation approach for identifying the underlying systems in a NARMA-L2 configuration. The controllers are applied to control two compositions of a binary distillation column, which has been modelled and simulated in MATLAB® and on the Simulink® platform. Comparative analysis has been undertaken to investigate the controllers' performance, which shows that PID-like FLC outperforms the other tested fuzzy control configurations, i.e. PI- and PD-like. Moreover, PSO has been found to outperform GA in finding the best set of scaling factors and over a shorter time period. Subsequently, the performance of PID-like FLC has been compared with ANN-based NARMA-L2 and the proposed ANFIS-based NARMA-L2, by subjecting the controlled column to different test scenarios. Furthermore, the stability and robustness of the controllers have been assessed by subjecting the controlled column to inputs variance and disturbances situations. The proposed ANFIS-based NARMAL2 controller outperforms and demonstrates more tolerance of disturbances than the other controllers. Finally, the study has involved investigating the control of a multicomponent distillation column due to its significant enhancement in operational efficiency regarding energy saving and recent widespread implementation. That is, Kaibel's distillation column with 4×4 configuration has been simulated also in MATLAB® and on the Simulink® platform with the proposed controller being implemented to control the temperatures of the column and the outcomes subsequently compared with conventional PID controllers. Again, the novel controller has proven its superiority regarding the disturbances tolerance as well as dealing with the high dynamics and nonlinear behaviour.
21
Prasad, Badri Krishnamurthy 1959. "Experimental investigation of sleeved columns." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277134.
Full textAbstract:
Results of experimental tests are presented for twelve 'Sleeved Column' specimens. All the specimens had an outer sleeve and an inner core, both of rectangular cross section. Outer sleeve was 23 in. long and the inner core was 23.5 in., with axial load applied only to the core. There was a gap between the sleeve and the core for all specimens except for one which had zero gap. The parameters considered for the study were core thickness and gap. It was concluded from the study that the sleeved column system carries substantially more load than the conventional Euler's column. The stiffness of the core and the gap between the sleeve and the core affects the load carrying capacity of sleeved column system significantly. For the same core size, specimens with least gap carried more load when compared to other specimens with larger gaps.
22
Rahimi, Rahbar. "Heat transfer in bubble columns." Thesis, University of Bath, 1988. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380868.
Full text
23
Yang, Guoqiang. "Bubble formation dynamics and transport phenomena in high pressure bubble columns and slurry bubble columns /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486474078051133.
Full text
24
Koen, Johan Alexander. "An investigation into the axial capacity of eccentrically loaded concrete filled double skin tube columns." Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/96797.
Full textAbstract:
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.
25
Borsatto, João Victor Basolli. "Colunas empacotadas em cromatografia líquida capilar: desenvolvimento de hardwares e avaliação de suas contribuições no desempenho cromatográfico." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/75/75135/tde-23102018-170956/.
Full textAbstract:
Essa dissertação de mestrado descreve o desenvolvimento de hardwares de colunas para cromatografia líquida capilar. O processo de desenvolvimentos desses dispositivos é descrito gradativamente e os pontos fortes e as limitações de cada modelo de hardware são discutidos. O melhor modelo de hardware desenvolvido apresentou produção simples, fácil conexão ao sistema cromatográfico e resistência a pressões superiores a 900 bar. Sucessivamente ao estabelecimento de um modelo de hardware apropriado, os efeitos dos materiais do hardware na eficiência das colunas foram avaliados. Poucos estudos relatam a influência do hardware nas separações em escala capilar, de forma que essa dissertação contribui para o preenchimento dessa lacuna. Capilares de aço inoxidável e sílica fundida e frits de aço inoxidável e fibra de vidro foram avaliados. Colunas com eficiências superiores a 100.000 pratos por metro foram produzidas.This master\'s dissertation describes the development of hardware for capillary liquid chromatography columns. The development process of the devices is described gradually and the strengths and limitations of each model of hardware are discussed. The best-developed hardware model presented easy production, practice connection to the chromatographic system and resistance to pressures greater than 900 bar. After the establishment of an appropriate hardware model, the effects of hardware materials on the efficiency of the columns were evaluated. Few studies report the influence of the hardware on capillary scale separations; therefore, this dissertation contributes to fill this gap. Capillaries of stainless steel and fused silica and frits of stainless steel and glass fiber were evaluated. Columns with efficiencies greater than 100,000 plates per meter were produced.
26
Li, Yaqiong. "The Shaking Table Tests Column Database and evaluation of drift capacity models for non-ductile columns." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/40417.
Full textAbstract:
A Shaking Table Tests Column Database comprised of 59 reinforced concrete columns subjected to shaking table tests is compiled in this research. Key geometrical information, material properties and test data of the columns are provided and used to improve the seismic assessment of old reinforced concrete structures.
Several structural models estimating the column effective stiffness and drift capacities at shear failure and axial-load failure are evaluated. Models based on the design parameters, such as transverse reinforcement ratio and axial load ratio, generally underestimate the column drift at shear failure (loss of 20% of lateral resistant force) in the dynamic test. Empirical plastic drift capacity models for columns subjected to subduction earthquakes and general types of ground motions are proposed. For column drift at axial-load failure, models based on shear-friction mechanism could capture the drift capacity fairly well.
The provisions of the current seismic rehabilitation standard ASCE/SEI 41 Supplement 1 regarding the concrete columns are also evaluated with this dynamic database. It is found that this standard generally overestimates the column effective stiffness and could provide the mean value of the column shear strength. The modeling parameters specified in the standard provide fairly conservative estimate of the column drift capacities and are consistent with the targeted probability of failure. Refinements of the shear strength model and the criteria for column classifications are suggested in this research.
27
Monaco, Enzo. "pH Transients in Hydroxyapatite chromatography columns." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
Find full textAbstract:
Ceramic Hydroxyapatite (CHT), with empirical formula (Ca5(PO4)3OH)2, is a material used as ion exchange resin in chromatographic applications. The material, having both positive and negative charged sites, can be used in many different contexts encountered in the protein purification processes. Nevertheless, the resin shows an intrinsic limitation for this kind of applications: even if the material solubility in water is very low at pH values higher than 6.5, it sharply increases in more acidic environments, reducing the life of the material and increasing the operative costs of the process, making problematic the CHT application at these conditions.
There is a further complication related to the CHT application: it is experimentally reported that the result of the resin interactions with salts is a pH transient occurring in the liquid phase of the chromatographic column.
These pH variations are temporary but remarkable, they may influence in an important manner the material solubility, affecting the number of utilization cycle of the fixed bed and, eventually, the stability of the proteins involved in the separation process.
In this work the principal aspects contributing at the selection of the operating pH and of the buffering specie are analyzed, discussing also the effect of the buffer itself on the material solubility.
Then, it is reported a mathematical model useful for the description of the dynamic behavior of the column and it is proposed an interaction mechanism between the salts of the mobile phase and the stationary phase. In particular, it is emphasized the discussion regarding the different affinity shown by the stationary phase for the different counter-ions which may accompanies the buffering specie.
Finally, a series of equations are developed at the scope to obtain a model useful to describe the observed pH transients.
28
Golden, James Hollis. "Ammonia - water desorption in flooded columns." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44884.
Full textAbstract:
Refrigeration systems employing the NH3-H2O absorption cycle provide cooling using a thermal energy input. This cycle relies on the zeotropic nature of the refrigerant - absorbent pair: because of the difference in boiling temperatures between NH3 and H2O, they can be separated through selective boiling in the desorber. Desorbers with counter-current flow of the solution and generated vapor enable efficient heat and mass transfer between the two phases, reducing the absorbent content in the generated vapor.
Flow visualization experiments at temperatures, concentrations and pressures representative of operating conditions are necessary to understand the heat and mass transfer processes and flow regime characteristics within the component. In this study, a Flooded Column desorber, which accomplishes desorption of the refrigerant vapor through a combination of falling-film and pool boiling, was fabricated and tested. Refrigerant-rich solution enters the top of the component and fills a column, which is heated by an adjacent heated microchannel array. The vapor generated within the component is removed from the top of the component, while the dilute solution drains from the bottom.
Flow visualization experiments showed that the Flooded Column desorber operated most stably in a partially flooded condition, with a pool-boiling region below a falling-film region. It was found that the liquid column level was dependent on operating conditions, and that the pool-boiling region exhibits aggressive mixing between the vapor and solution phases.
Heat transfer coefficients were calculated from the data for the pool-boiling region, and were compared with the predictions of several mixture pool-boiling correlations from the literature. The correlations from the literature were in general unable to predict the data from this study adequately. It was found that the Flooded Column desorber yielded higher heat transfer coefficients within the pool-boiling region than those predicted by these correlations. Therefore, modifications to existing mixture boiling correlations are suggested based on the findings of this study. The resulting modified correlation predicts 33 of the 35 data points from this study within ±40%, with an average absolute error of 19%.
29
Bournine, Hadjila. "Bolted friction columns for structural damping." Thesis, University of Bristol, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555725.
Full textAbstract:
Over the last three decades, friction damping has been proved to be very efficient for vibration mitigation. The designs developed so far are either bracing mechanisms or friction joints. The aim of this thesis is to investigate the feasibility of friction columns for vibration damping. A friction column is composed of two steel beams bolted together allowing dynamic friction to occur at the interface. The mechanism has been proved to dissipate a large amount of the vibration energy. The energy dissipated by friction depends on both the bolt tension forcing the beams together and the relative displacement at the interface. Therefore, a model relating the relative displacement at the interface to the deflection of the friction column was developed and experimentally investigated. The results assisted in defining a hysteretic friction-slip model and the conditions causing the stick and slip transitions. The results showed that the damping in the friction column could be improved up to ten. times its inherent viscous damping when the bolts tension is properly optimised. The presence of friction in the column does not only affect its damping properties but also its stiffness. A model depicting the effect of friction on the dynamics of the column was derived from first principles and experimentally validated. The friction column was then placed in a frame context. Despite the fact that both ends of the friction column were restrained, the relative displacement at the interface was large. This is due to the non monotonic nature of the modeshapes during lateral vibration. This also increases the friction force magnitude which allows the column to slip at higher bolt tensions and lower deflection magnitudes compared to the cantilever. This proved that friction columns can provide valuable damping and prevent irreversible damage to the structure . •.
30
Elghazouli, Ahmed Youssef. "Earthquake resistance of composite beam-columns." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/7906.
Full text
31
Bhola, Rajendra Kumar. "Reliability of slender reinforced concrete columns." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25079.
Full textAbstract:
The effects of the variability in strength and loading on the reliability of slender, reinforced concrete columns are investigated using the Monte Carlo simulation technique. The columns are considered to be axially loaded with equal end eccentricities and no lateral load.
Variabilities in strength, axial load and eccentricity of axial loads are considered. A new procedure called the Implicit Uncorrelation Procedure has been developed to find the values of the failure function from the values of the basic variables named above.
The allowable axial load at various eccentricity levels corresponding to a probability of failure of one in one hundred thousand has been found for three different cross sections. Seven different slenderness ratios are considered for each cross section. The results are compared with those obtained by following the code procedures outlined in CAN3-A23.3-M77 and CSA-A23.3 (1984).
A change in the performance factor for moment magnification, ⌀m , (as given in CSA-A23.3 (1984)) is recommended in order to obtain a more accurate and consistent level of reliability in the design of slender reinforced concrete columns.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
32
Lloyd, Alan Eric Walker. "Blast Retrofit of Reinforced Concrete Columns." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32389.
Full textAbstract:
Explosives place large demands on the lateral load carrying capacity of structures. If these loads are applied on columns, the high pressure transient loads from explosives can result in significant damage to the primary gravity load carrying elements. The loss of these elements, which are responsible from overall strength and stability of the structure, may cause collapse of all or parts of the structure. Therefore, it is important to mitigate the blast loads effects on columns. A comprehensive research study into the design, application, and use of different retrofit systems to mitigate damage to columns under blast loads has been undertaken. This research program, consisting of experimental testing and analytical investigation, sought out retrofits that address the strength of columns as well as those that enhance ductility are explored. Different materials and resistance mechanisms are used to increase column capacity. An experimental testing program was conducted using a shock tube to test the capacity of columns under blast loads. For this program, a total of sixteen reinforced concrete columns were constructed and the data from a further two columns from a previous study was compiled. Of these columns, a total of thirteen were retrofitted to mitigate the effects of blast. Carbon fibre reinforced polymer (CFRP) was applied to eight of the columns in the form of jacketing, longitudinal reinforcement, or the combination of the two. The other retrofits included steel prestressed confinement applied to one column, steel bracing acting as compression members applied to one column, and steel bracing acting as tension members applied to three columns. The columns were tested under incrementally increasing shock tube induced shock wave loading up to failure of the specimen or capacity of the shock tube. The performance of the retrofitted columns was compared with the control columns and against other retrofits. Quantitative comparisons of displacements and strains were made along with qualitative assessments of damage. The results indicated that all the retrofits increased capacity to the column, however, certain retrofits out performed others. The best FRP retrofit technique was found to be the combination of longitudinal and transverse FRP. The prestressed steel jacketing proved to be effective at increasing ductility capacity of the column. The compression brace retrofit was found to be effective in significantly increasing capacity of the column. The tension brace retrofits had the best performance over all the retrofits including the compression brace retrofit. The experimental data was used to validate analysis techniques to model the behaviour of the specimens. This technique reduced the columns to an equivalent single-degree-of-freedom (SDOF) system for dynamic analysis purposes. The reduction to the SDOF system was achieved by computing a resistance to lateral load and lateral displacement relationship. Each retrofit was carefully considered in this analysis including the retrofit’s possible effect on material and sectional properties as well as any force resistance mechanism that the retrofit introduces. The results of the modeling and experimental program were used to develop retrofit design guidelines. These guidelines are presented in detail in this thesis.
33
Bugaldian, Adel Abdulmoula. "Concrete columns confined with scrap tires." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0022/MQ52289.pdf.
Full text
34
Deng, Ying 1972. "Confinement of columns using headed bars." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=31047.
Full textAbstract:
Eight full-scale columns were constructed and tested under monotonic axial compression loading to investigate the influence of headed bars on the confinement of the concrete. One column represented a column with no transverse reinforcement and another column had poor detailing and little confinement. A third column contained seismic hoops and crossties, which represented current detailing practice for significant confinement. A fourth column test investigated the response with the seismic crossties replaced by headed bars. Finally, two column specimens were constructed and tested with all of the transverse reinforcement provided by headed bars. These six specimens enabled an assessment of the effectiveness of headed bars in confining the concrete. It was found that the use of headed bars improved the confinement of the columns.Two additional specimens were constructed without any transverse reinforcement. These columns were later retrofitted, by drilling horizontal holes in the columns, adding special headed bars (one head fixed and one head threaded) and then filling the drilled holes with epoxy. These retrofitted specimens had two different spacings for the added headed bars. The improvement of the response with these added headed bars provided insight into the rehabilitation of older structures containing poorly detailed columns. All of the test specimens were instrumented to determine strain localization during failure and to monitor the strains in the longitudinal and transverse reinforcement.
35
羅紹湘 and Siu-seong Law. "Failure of reinforced concrete beam-columns." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1985. http://hub.hku.hk/bib/B31207327.
Full text
36
蔡燦茂 and Tsan-mau Choi. "Flow and mixing in packed columns." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31214034.
Full text
37
Schenk, Myrian Andrea. "Design of operable reactive distillation columns." Thesis, University College London (University of London), 1999. http://discovery.ucl.ac.uk/1382008/.
Full textAbstract:
Reactive distillation is an integrated process which considers simultaneous physical and chemical transformations. It is increasingly receiving attention both from industry and academia. Significant advances have been made in the area of modelling and simulation as well as the implementation of such units industrially. However, the area of control and optimisation of such units has not been explored thoroughly. The thesis presents a general framework for simulation and design, which can handle reactive and non-reactive systems. Various different aspects of the modelling and simulation of distillation have been described in order to understand the behaviour of the reactive distillation columns. In the framework both simulation modes, steady-state and dynamic, are considered and the process is described by equilibrium and non equilibrium-based models. In a rate-based (or non equilibrium) model, mass transfer rates between liquid and vapour phase are considered explicitly, based on the Maxwell-Stefan equations. Equilibrium is attained at the phase interface in the non-equilibrium model. A switching policy makes it possible to go from one model to the other, based on the knowledge gained, by following the Gibbs free energy as a function of time. Tray efficiency has also helped in determining the switch between the non-equilibrium and equilibrium models, and has been studied for various systems. The existence of multiple steady state has been verified through simulation with the hybrid model. Bifurcation diagrams also confirmed the existence of output multiplicity obtained in the simulations. Analysis of process controllability at the design stage has been shown to provide guidance for improving process operation. In the thesis controllability measures for the reactive systems studied are presented as a first step towards control structure selection. A method for obtaining the design of reactive separation columns at minimum total annualised cost (investment and operating costs) and which will be able to maintain stable operation in the presence of variability is also presented.
38
Maciel, Marina Regina Wolf. "Interactive design of multicomponent distillation columns." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328952.
Full text
39
Mahdmina, Ali. "Modelling and control of distillation columns." Thesis, University of Manchester, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277212.
Full text
40
Stark, M. S. "The optogalvanic effect in positive columns." Thesis, University of York, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372761.
Full text
41
Morisco, I. "Inelastic behaviour of steel beam-columns." Thesis, City University London, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373327.
Full text
42
Lillistone, Duncan. "Non-ferrous compositely reinforced concrete columns." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364791.
Full text
43
JURJO, DANIEL LEONARDO BRAGA RODRIGUEZ. "STABILITY OF COLUMNS UNDER SELF-WEIGHT." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2001. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=1978@1.
Full textAbstract:
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICONesta dissertação são estudados a flambagem e o comportamento pós-crítico de colunas esbeltas sob a ação do peso próprio. Primeiramente, é realizada uma análise linear para a determinação das cargas críticas e modos críticos para colunas com diferentes condições de contorno e para a determinação da relação carga-frequência. Para estudar o comportamento pós-crítico da coluna, uma formulação geometricamente exata para a análise não-linear de elementos estruturais unidimensionais foi desenvolvida, considerando uma distribuição arbitrária da carga e condições de contorno. A partir desta formulação obtém-se um conjunto de equações não-lineares de primeira ordem, as quais,juntamente com as condições de contorno dos extremos da coluna, formam o problema de valor de contorno. Este problema é resolvido pelo uso simultâneo do método de integração numérica de Runge-Kutta e pelo método de Newton- Raphson. Devido a um algorítmo de continuação, soluções precisas podem ser obtidas para uma variedade de problemas de estabilidade apresentando pontos limite ou de bifurcação. Com o uso desta formulação, é feita uma análise paramétrica detalhada a fim de possibilitar o estudo da flambagem e do comportamento pós-crítico de colunas esbeltas sujeitas a ação do peso próprio, incluindo a influência das condições de contorno na estabilidade, a distribuição dos esforços internos e o comportamento não- linear geométrico da coluna. Com o objetivo de verificar a qualidade e a precisão dos resultados, foi conduzida uma análise experimental para o caso de uma coluna esbelta engastada e livre. Os resultados experimentais obtidos para a flambagem, freqüências naturais e para o comportamento pós-crítico foram comparados de forma favorável com os resultados teóricos e numéricos.
In this thesis the buckling and post-buckling behavior of slenders columns under self-weight are studied. First a linear analysis is conducted to determine the critical loads for different boundary conditions and the load-frequency relation. In order to study the post-buckling behavior of the column, a geometrically exact formulation for the non- linear analysis of uni-dimentional structural elements has been derived, considering arbitrary load distribution and boundary conditions. From this formulation one obtains a set of first-order coupled non-linear equations which, together with the boundary conditions at the column ends, form a two-point boundary value problem. This problem is solved by the simultaneous use of the Runge-Kutta integration scheme and the Newton-Raphson method. By virtue of a continuation algorithm, accurate solutions can be obtained for a variety of stability problems exhibiting either limit point or bifurcational-type buckling. Using this formulation, a detailed parametric analysis is conducted in order to study the buckling and post-buckling behavior of slender columns under self-weight, including the influence of boundary conditions on the stability, internal forces distribution and large deflection behavior of the column. To verify the quality and accuracy of the results, an experimental analysis was conducted considering a clamped-free thin-walled metal column. The buckling and post-buckling behavior as well as the load-frequency relation were obtained and compared favorably with the theoretical and numerical results.
En esta disertación se estudian el flameo el comportamiento postcrítico de columnas esbeltas bajo la acción del peso proprio. Primeramente, se realiza un análisis lineal para la determinación de las cargas críticas y modos críticos para columnas con diferentes condiciones de contorno y para la determinación de la relación carga frecuencia. Para estudiar el comportamiento postcrítico de la columna, fue desarrollada una formulación geométricamente exacta para el análisis no lineal de elementos extructurales unidimensionales, considerando una distribuición arbitraria de la carga y condiciones de contorno. A partir de esta formulación se obtiene un conjunto de ecuaciones no lineales de primer orden, las cuales, juntamente con las condiciones de contorno de los extremos de la columna, forman el problema de valor de contorno. Este problema se resuelve usando simultáneamente el método de integración numérica de Runge Kutta y el método de Newton Raphson. A través de un algorítmo de continuación, pueden ser obtenidas soluciones precisas para una variedad de problemas de estabilidad presentando puntos límite o de bifurcación. Utilizando esta formulación, se realiza análisis paramétrico detallado a fin de hacer posible el estudio del flameo y del comportamiento postcrítico de columnas esbeltas sujetas a la acción del proprio peso, inclyendo la influencia de las condiciones de contorno en la estabilidad, la distribuición de los esfuerzos internos y el comportamiento no lineal geométrico de la columna. Con el objetivo de verificar la calidad y la precisión de los resultados, se ejecutó un análisis experimental para el caso de una columna esbelta y libre. Los resultados experimentales obtenidos para el flameo, frecuencias naturales y para el comportamiento postcrítico fueron comparados de forma favorable con los resultados teóricos y numéricos.
44
Urua, Ini Johnson. "Foaming in distillation and absorption columns." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47291.
Full text
45
Welp, Katherine Marie 1958. "Effective stiffness of rectangular concrete columns." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276822.
Full textAbstract:
This thesis is based upon a need to re-examine the assumptions and expand upon the results arrived at in recent studies on the flexural stiffness of reinforced concrete columns. A survey is presented of concrete column design over the last 200 years. Elastic and plastic behavior of concrete columns is discussed with respect to stiffness and Euler's buckling load. Some limitations and applications of buckling load are considered. Various current code approximations of stiffness are presented. Four possible methods for computing a more exact stiffness (EI) and their advantages and disadvantages are discussed. The formula EI = M/φ provides the best solution. The two dimensional program RECTCOL which is based on the P-M-φ relationships is developed and explained. Then RECTCOL is used to show how the column flexural stiffness varies with axial load, reinforcement ratio, yield strength of the reinforcing steel, concrete strength, cover, and column dimensions. A flow chart and source code are included by RECTCOL.
46
Harvey-Doyle, Fiona. "Resistively heated columns for liquid chromatography." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/6370.
Full textAbstract:
Interest in temperature as a modifier in HPLC separations has increased markedly recently due to miniaturisation, new stable hybrid stationary phases and the use of superheated water as an eluent. However, for decades temperature has generally been regarded as a parameter that should be kept constant in LC separations for retention reproducibility but there is now a mountain of journal papers supporting the use of this variable. Currently, the limit of implementation usually arises from the lack of LC ovens on the market capable of high temperature applications. This led to the development of a resistively heated LC oven which allowed rapid reproducible heating/cooling patterns of RP columns thus reducing equilibration times and realising high sample throughput. The main objective was to drive temperature programming to a new extreme by rapid column heating akin to GC rather than LC, the emphasis being to produce much sharper peaks very rapidly. It was hoped that temperature gradients could replace solvent gradients and extend the applicability of temperature-programming for hyphenation to other forms of detection. New column materials were sought and tested against high speed temperature gradients. This coupled with micro-column technology should reduce analysis time and appreciably limit the amount of solvent waste currently being generated by conventional LC techniques. The column heating was achieved by two system components, the oven and the eluent pre-heater unit both based on resistive heating. Post-column cooling prior to detection minimised baseline disturbances imposed by a temperature gradient and enabled the use of detection modes such as MS, RI and ELSD as well as UV spectroscopy.
47
Wilson, William Henry. "Packed capillary columns for liquid chromatography." Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/37746.
Full text
48
Ali, Syed Aftab. "Semi-Packed Micro Gas Chromatography Columns." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/35201.
Full textAbstract:
Separation of complex gaseous mixtures using gas chromatography (GC) is an important step in analytical systems for environmental monitoring, medical diagnosis, and forensic science. Due to its high resolving power, analysis speed, and small sample size, GC, has become the premier technique for separation and analysis of volatile and semi-volatile organic compounds. Miniaturization of analytical systems has become a major trend which is mainly driven by advancements in microfabrication techniques and a need for portable lab-on-a-chip systems for onsite monitoring. Microfabricated columns have been explored for applications in analytical processes like GC in several research studies. These microGC columns typically have open rectangular or open circular cross sections which is a result of the etching process utilized in the fabrication. This work reports the fabrication and performance of a new generation of silicon-on-glass micro-electro-mechanical systems (MEMS) based GC columns with microposts namely â semi-packed.â These columns can be fabricated on a 2 cm2-die for a 1 m-long channel or a 1 cm2-die for a 25 cm-long channel. The semi-packed columns have a higher sample capacity as the overall surface area is larger than that of open rectangular columns of the same dimensions. The separation efficiency of these columns is also superior to that of open columns due to the presence of the microposts. As compared to conventional packed columns, the semi-packed columns show lower pressure drops and a more uniform flow profile, both of which contribute to, performance in terms of separation efficiency.Master of Science
49
Jowhari, Moghadam Shirin. "Plastic buckling of columns and plates." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/29865.
Full textAbstract:
The theory of buckling strength of compression members in the plastic range has been extensively studied, and numerical methods already exist which deal with such behaviour. However, there is a significant research interest in developing analytical models for the plastic buckling, largely driven by the need for simplified mechanics based design tools, but also by the desire for enhanced understanding of this complex phenomenon. A thorough investigation into the inelastic buckling of columns and plates reveals the existence of two well-known inconsistencies recognised as the 'Column Paradox' and the 'Plate Plastic Buckling Paradox'. In the current research, addressing the conceptual issues related to the plastic buckling of columns and plates, including the two associated paradoxes, has been achieved by means of development and application of analytical models that are verified against nonlinear finite element analysis. These models are based on sound principles of structural mechanics and are intended to illustrate the mechanics of the plastic buckling response of stocky columns/plates by means of a simplified analytical approach, from the point of buckling initiation and considering the post-buckling response. In these models, the Rotational Spring Analogy is used for formulating the geometric stiffness matrix, whereas the material stiffness matrix is obtained with due consideration for the spread of material plasticity. It is shown that the buckling of stocky perfect columns starts at the Engesser load while the von Karman upper limit is typically not realised due to tensile yielding at the outer fibre of the column cross-section. Furthermore, it is established that beyond a threshold level of imperfection, as evaluated directly from the developed model, the plastic post-buckling response of columns is barely affected by a further increase in the out-of-straightness. Besides identifying previous misconceptions in the research literature, the proposed analytical models for the plastic buckling of plates have proven to offer valuable insight into factors that influence the plastic buckling of stocky plates, and hence succeeded in resolving the long-standing paradox. It is the major contention of this thesis, verified through extensive studies, that the 'Plate Plastic Buckling Paradox' is resolved with the correct application of plasticity theory, considering not only the influence of initial imperfections but also the interaction between flexural and planar actions.
50
Choi, Tsan-mau. "Flow and mixing in packed columns /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B17389872.
Full text