In this work the experimental results from the rapid screening and ranking of a wide range of novel adsorbents for carbon capture are presented. The samples were tested using the Zero Length Column (ZLC) method which has proved to be an essential tool for the rapid investigation of the equilibrium and kinetic properties of prototype adsorbents. The study was performed on different classes of nanoporous materials developed as part of the EPSRC-funded “Innovative Gas Separations for Carbon Capture” (IGSCC) project. More than 120 novel adsorbents with different key features for post-combustion carbon capture were tested. The classes of materials investigated were: • PIMs (Polymers of Intrinsic Microporosity) • MOFs (Metal - Organic Frameworks) • Mesoporous Silica • Zeolites • Carbons All the samples were tested at experimental conditions close to the ones of a typical flue gas of a fossil fuel power plant: 35 ºC and 0.1 bar of partial pressure of CO2. The results from the ranking of the CO2 capacity of the materials, at the conditions of interest, indicate the Mg and Ni-based MOF samples as the adsorbents with the highest uptake among all the candidates. The best sample shows a CO2 capacity almost double than the benchmark adsorbent, zeolite 13X (provided by UOP). The ranking also shows some of the zeolite adsorbents synthesised as promising materials for carbon capture: uptakes comparable or slightly higher than 13X were obtained for several samples of Rho and Chabazite zeolite. Water stability tests were also performed on the best MOFs and showed a deactivation rate considerably faster for the Mg-based MOFs, proving an expected higher resistance to degradation for the Ni based materials. A focused investigation was also carried out on the diffusion of CO2 in different ionexchanged zeolites Rho samples. The study of these samples, characterised by extremely slow kinetics, extended the use of the ZLC method to very slow diffusional time constants which are very difficult to extract from the traditional long time asymptotic analysis. The results show how the combination of the full saturation and partial loading experiment can provide un-ambiguous diffusional time constants. The diffusivity of CO2 in zeolite Rho samples shows to be strongly influenced by the framework structure as well as the nature and the position of the different cations in the framework. The kinetics of the Na-Cs Rho sample was also measured by the use of the Quantachrome Autosorb-iQ™ volumetric system. To correctly interpret the dynamic response of the instrument modifications were applied to the theoretical model developed by Brandani in 1998 for the analysis of the piezometric method. The analytical solution of the model introduces parameters which allow to account for the real experimental conditions. The results confirm the validity of the methodology in the analysis of slow diffusion processes. In conclusion the advantages offered by the small size of the column and the small amount of sample required proved the ZLC method to be a very useful tool for the rapid ranking of the CO2 capacity of prototype adsorbents. Equilibrium and kinetic measurements were performed on a very wide range of novel nanoporous materials. The most promising and interesting samples were further investigated through the use of the water stability test, the partial loading experiment and the volumetric system. The ZLC technique was also extended to the measurements of systems with very slow kinetics, for which is very difficult to extract reliable diffusional time constants. An improved model for the interpretation of dynamic response curves from a non-ideal piezometric system was developed.

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.

In structural concrete, hooked bars are used to shorten anchorage length when the requirements for straight bar anchorage cannot be provided within the available dimensions of elements. The objective of this study was to provide an overview of hooked bar anchorage. Design examples and structural details are based on Building code requirements for structural concrete (ACI 318-08) and commentary. Examples of standard hooks in exterior beam-column joint and hooked bar anchorage details for reinforced concrete beam-SRC column joints are discussed. The general behavior of anchorage of hooked reinforcing bars is summarized from a review of previous studies. Then, design requirements for the development length of standard hook are discussed and used in an example. An example of the use of hooked bars in reinforced concrete beam-SRC column joint is provided. Four options for short development length are presented and compared: Adding more reinforcement, welding bars, confinement by steel column flanges, and anchorage by plate welded between flanges. / text

Froth flotation is a widely used, cost effective particle separation process. However, its high performance is limited to a narrow particle size range, e.g., between 50 µm and 600 µm for coal and between 10 µm and 100 µm for minerals. Outside this range, the efficiency of froth flotation decreases significantly, especially for difficult-to-float particles of weak hydrophobicity (e.g., oxidized coal). Nanobubbles integrated into a specially designed column flotation expanded the particle size range for efficient froth flotation as a result of increased probabilities of particle- bubble collision and attachment and reduced probability of detachment. The major advantages of nanobubble enhanced flotation include lower collector and frother dosages since nanobubbles that are mostly smaller than 1 µm can be formed selectively on hydrophobic coal particles from dissolved air in coal slurry. Nanobubbles act as a secondary collector on particle surfaces, thereby resulting in considerably lower operating costs. A systematic parametric investigation of the proposed technology was performed to understand the effects of process variables on separation performance with a typical coal sample using a specially designed flotation column and three 10-liters conventional flotation cells. Results indicate that the combustible recovery of a -150 µm coal increased by 5-50% in the presence of nanobubbles, depending on process operating conditions. Nanobubbles also significantly improved process separation efficiency and increased the flotation rate constant by more than 40%. Theoretical evaluation of the innovative flotation technology was employed using specially designed apparatus to study the nanobubbles stability and the roles of nanobubbles on particle-bubble interactions, froth stability, and surface area flux. In addition, a detailed technical performance and economic evaluation was performed.

Most traditional routing problems assume perfect operability of all arcs and nodes. However, when independent arc failure probabilities exist, a secondary objective must be present to retain some measure of expected functionality. We first briefly consider the reliability-constrained single-path problem, where we look for the lowest cost path that meets a reliability side constraint. This analysis enables us to then examine the reliability-constrained two-path problem, which seeks to establish two minimum-cost paths between a source and destination node wherein at least one path must remain fully operable with some threshold probability. We consider the case in which both paths must be arc-disjoint and the case in which arcs can be shared between the paths. We prove both problems to be NP-hard. We examine strategies for solving the resulting nonlinear integer program, including pruning, coefficient tightening, lifting, and branch-and-bound partitioning schemes. Next, we consider the reliable h-path routing problem, which seeks a minimum-cost set of h ≥ 2 arc-independent paths between a source and destination node, such that the probability that at least one path remains operational is sufficiently large. Our prior arc-based models and algorithms tailored for the case in which h = 2 do not extend well to the general h-path problem. Thus, we propose two alternative integer programming formulations for the h-path problem in which the variables correspond to origin-destination paths. We propose two branch-and-price-and-cut algorithms for solving these new formulations, and provide computational results to demonstrate the efficiency of these algorithms. Finally, we examine the robust design of an evacuation tree, in which evacuation is subject to capacity restrictions on arcs. Given a discrete set of disaster scenarios with varying network populations, arc capacities, transit times, and time-dependent penalty functions, we seek to establish an optimal a priori evacuation tree that minimizes the expected evacuation penalty. The solution strategy is based on Benders decomposition, and we provide effcient methods for obtaining primal and dual sub-problem solutions. We analyze techniques for strengthening the master problem formulation, thus reducing the number of master problem solutions required for the algorithm's convergence.

Applying lateral confinement to concrete columns using fibre-reinforced polymer (FRP) composites is a very promising technique. FRP rupture is the typical failure mode of FRP wrapped columns under axial compression. numerous experiments have shown that the FRP rupture strain in an FRP wrapped circular column is significantly lower than the FRP ultimate rupture strain determined from flat coupon test of FRP. Despite a large number of studies on the application of FRP confined columns, the mechanisms and level of lower-than-apparent FRP rupture strain still remain unclear. This thesis presents theoretical, Numerical and experimental studies aiming at developing a deeper understanding of the fundamental mechanisms of this phenomenon. A comprehensive literature review was presented providing the background on FRP confined columns, material properties of FRP composites as well as some factors which may lead to premature FRP rupture. A FE analysis was conducted to investigate the FRP hoop strains in the split-disk test, explaining for the first time that the fundamental mechanism of the lower FRP rupture strain in the split-disk test than in the flat coupon test is because strain localisation due to geometric discontinuities at the ends of the FRP and bending of the FRP ring at the gap due to change of curvature caused by the relative moment of the two half disks, as the FRP (as a brittle material) ruptures once the maximum strain at one of these locations reaches the FRP rupture strain. A list of contributory factors affecting the apparent FRP rupture strain in FRP wrapped columns were next identified and classified. An analytical solution was developed to investigate the influence of the triaxial stress state on the FRP strain efficiency, this factor has been shown to have a potentially significant effect on the failure of the FRP wrap but considerable discrepancies exist between predictions using different failure criteria so further research has been identified in this area. FE models were developed to examine the effect of the geometrical discontinuities on the strain efficiency of FRP jackets in FRP wrapped concrete-filled circular steel tubes and FRP wrapped concrete columns. It is demonstrated that severe FRP hoop strain concentrations occur in very small zones near the ends of the FRP wrap in both types of FRP wrapped columns, leading to premature FRP rupture and thus lower strain efficiency. The combined effects of end constraint and FRP overlap on the behaviour of FRP wrapped concrete columns was investigated using a three dimensional FE model considering one half of the length of an FRP-wrapped concrete cylinder. The results have shown that the frication between both ends of a column and the loading platens provides constraints to the ends of the column, but this constraint has little effect on the strain concentration caused by the geometrical discontinuities of the FRP overlap, though the ultimate axial strain of the FRP wrapped columns can be significantly overestimated if the end constraints are not considered.

In this thesis we study how to efficiently combine the column generation technique (CG) and interior point methods (IPMs) for solving the relaxation of a selection of integer programming problems. In order to obtain an efficient method a change in the column generation technique and a new reoptimization strategy for a primal-dual interior point method are proposed. It is well-known that the standard column generation technique suffers from unstable behaviour due to the use of optimal dual solutions that are extreme points of the restricted master problem (RMP). This unstable behaviour slows down column generation so variations of the standard technique which rely on interior points of the dual feasible set of the RMP have been proposed in the literature. Among these techniques, there is the primal-dual column generation method (PDCGM) which relies on sub-optimal and well-centred dual solutions. This technique dynamically adjusts the column generation tolerance as the method approaches optimality. Also, it relies on the notion of the symmetric neighbourhood of the central path so sub-optimal and well-centred solutions are obtained. We provide a thorough theoretical analysis that guarantees the convergence of the primal-dual approach even though sub-optimal solutions are used in the course of the algorithm. Additionally, we present a comprehensive computational study of the solution of linear relaxed formulations obtained after applying the Dantzig-Wolfe decomposition principle to the cutting stock problem (CSP), the vehicle routing problem with time windows (VRPTW), and the capacitated lot sizing problem with setup times (CLSPST). We compare the performance of the PDCGM with the standard column generation method (SCGM) and the analytic centre cutting planning method (ACCPM). Overall, the PDCGM achieves the best performance when compared to the SCGM and the ACCPM when solving challenging instances from a column generation perspective. One important characteristic of this column generation strategy is that no speci c tuning is necessary and the algorithm poses the same level of difficulty as standard column generation method. The natural stabilization available in the PDCGM due to the use of sub-optimal well-centred interior point solutions is a very attractive feature of this method. Moreover, the larger the instance, the better is the relative performance of the PDCGM in terms of column generation iterations and CPU time. The second part of this thesis is concerned with the development of a new warmstarting strategy for the PDCGM. It is well known that taking advantage of the previously solved RMP could lead to important savings in solving the modified RMP. However, this is still an open question for applications arising in an integer optimization context and the PDCGM. Despite the current warmstarting strategy in the PDCGM working well in practice, it does not guarantee full feasibility restorations nor considers the quality of the warmstarted iterate after new columns are added. The main motivation of the design of the new warmstarting strategy presented in this thesis is to close this theoretical gap. Under suitable assumptions, the warmstarting procedure proposed in this thesis restores primal and dual feasibilities after the addition of new columns in one step. The direction is determined so that the modi cation of small components at a particular solution is not large. Additionally, the strategy enables control over the new duality gap by considering an expanded symmetric neighbourhood of the central path. As observed from our computational experiments solving CSP and VRPTW, one can conclude that the warmstarting strategies for the PDCGM are useful when dense columns are added to the RMP (CSP), since they consistently reduce the CPU time and also the number of iterations required to solve the RMPs on average. On the other hand, when sparse columns are added (VRPTW), the coldstart used by the interior point solver HOPDM becomes very efficient so warmstarting does not make the task of solving the RMPs any easier.

This thesis describes a stochastic ship routing problem with inventory management. The problem involves finding a set of least costs routes for a fleet of ships transporting a single commodity when the demand for the commodity is uncertain. Storage at consumption and supply ports is limited and inventory levels are monitored in the model. Consumer demands are at a constant rate within each time period in the deterministic problem, and in the stochastic problem, the demand rate for a period is not known until the beginning of that period. The demand situation in each time period can be described by a scenario tree with corresponding probabilities. Several possible solution approaches for solving the problem are studied in the thesis. This problem can be formulated as a mixed integer programming (MIP) model. However solving the problem this way is very time consuming even for a deterministic problem with small problem size. In order to solve the stochastic problem, we develop a decomposition formulation and solve it using a Branch and Price framework. A master problem (set partitioning with extra inventory constraints) is built, and the subproblems, one for each ship, involve solving stochastic dynamic programming problems to generate columns for the master problem. Each column corresponds to one possible tree of schedules for one ship giving the schedule for the ship for all demand scenarios. In each branch-and-bound node, the node problem is solved by iterating between the master problem and the subproblems. Dual variables can be obtained solving the master problem and are used in the subproblems to generate the most promising columns for the master problem. Computational results are given showing that medium sized problems can be solved successfully. Several extensions to the original model are developed, including a variable speed model, a diverting model, and a model which allows ships to do extra tasks in return for a bonus. Possible solution approaches for solving the variable speed and the diverting model are presented and computational results are given.

Master of Science / Department of Civil Engineering / Asadollah Esmaeily / Bridge and building construction in areas that sustain frequent seismic activity require the use of heavy lateral steel reinforcement within concrete columns to handle the lateral loads. Multi-spiral lateral reinforcement has been recently introduced to the construction field to offer an alternative to the traditional hoop and tie reinforcement. This report evaluates the experimental data observed in multiple experimental studies done on different concrete specimens. These specimens include multiple rectilinear reinforcement and several multi-spiral configurations in both rectangular and oblong columns. Due to multi-spiral reinforcement being a relatively new design, traditional computer programs have yet to include design analysis for this type of reinforcement in computer programs. Dr. Asad Esmaeily developed the program KSU RC 2.0 that can implement multiple analytical models to evaluate different multi-spiral configurations, as well as traditional hoop and tie confinement, that may be compared with experimental data. This report illustrates the comparative data from several different reinforced concrete column models. The data clearly indicates that multi-spiral reinforced columns exhibit higher compressive strength in the axial direction as well as higher ductility capabilities when compared to traditional rectilinear reinforcement of similar lateral steel reinforcement ratios. The use of multi-spiral reinforcement is also shown to lower costs for both the work time needed to install the structures as well as lowering the required steel ratio; all while maintaining the structural integrity of the columns.

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