This work is mainly concerned with the development of sophisticated yet efficient methods for assessing the elastic buckling of steel beams with web openings, focussing on local buckling effects in the web region. A new computational method is proposed which extends the use of the Element Free Galerkin (EFG) method for the numerical discretisation combined with a simplified buckling assessment approach based on the Rotational Spring Analogy (RSA). The new approach considers several potential simplifications offering a balance between computational efficiency and accuracy in local buckling analysis. In the present EFG/RSA method, considerable advantage is established by separating the planar and out-of-plane responses. Planar analysis is further enhanced using modular concepts, where the beam is divided into unit cells, each of which resembles a super-element with a reduced number of freedoms, and solved using a standard discrete procedure. As for the out-of-plane analysis, the application of a ‘local region’ is adopted to significantly reduce the size of the original buckling problem. Finally, local buckling assessment is conducted using an effective approach that utilises an iterative procedure based on a rank 2 reduced eigenvalue problem along with a shifting local region. Several illustrative examples are provided which highlight the efficiency and accuracy of the developed approach in comparison with detailed nonlinear finite element analysis performed using ADAPTIC, and which demonstrate general applicability to local buckling analysis of steel beams with web openings of various shapes and sizes. This work also considers the development of a simplified design-oriented method which is presented particularly for web-post buckling. Towards this end, a simplified analytical model is proposed based on an analogy with equivalent rectangular thin beams (RTB), where a semi-empirical approach is used to calibrate the suggested formulation against the results obtained from the numerical work performed earlier.

The femur‘s shape, geometry and internal structure are the result of bone‘s functional adaptation to resist the mechanical environment arising from different daily activities. Many studies have attempted to explain how this adaptation occurs by embedding bone remodelling algorithms in finite element (FE) models. However, simplifications have been introduced to the representation of bone‘s material symmetry and mechanical environment. Trabecular adaptation to the shear stresses that arise from multiple load cases has also been overlooked. This thesis proposes a novel iterative 3D adaptation algorithm to predict the femur‘s material properties distribution and directionality of its internal structures at a continuum level. Bone was modelled as a strain-driven adaptive continuum with local orthotropic symmetry and optimised Young‘s and shear moduli. The algorithm was applied to the Multiple Load Case 3D Femur Model, a FE model of a whole femur, with muscles and ligaments spanning between the hip and knee joints included explicitly. Several artificial structures were included to allow for more physiological modelling of the femur‘s mechanical behaviour. Multiple load cases representing different instances of daily activities were considered. The model‘s positioning and applied inter-segmental loading were extracted from a validated musculo-skeletal model. The mechanical envelope produced by the FE model was matched up with published studies and the model‘s suitability as a platform for the prediction of bone adaptation was confirmed. The resulting material properties distributions were compared against CT data of a human femur specimen and published studies. Furthermore, the predicted directionality of the femur‘s internal structures was validated by comparison with micro CT data of the proximal and distal regions of the same specimen. It was concluded that the proposed model can reliably produce the observed optimised structures in the femur. It is recommended that multiple activities and different instances of each load case should be considered when attempting to model bone‘s adaptation. The final result of this work is a physiological orthotropic heterogeneous model of the femur. This method has the potential to be an invaluable tool in achieving a more thorough understanding of bone‘s structural material properties, improving the knowledge we have of its mechanical behaviour.

The capacities of public transportation systems are limited in several ways: Among other limitations, there exist only a finite number of vehicles, space inside the vehicles is limited, and space inside the stations is limited. In this thesis a transit assignment model is used, where vehicle capacities are explicitly taken into account in the strategy choice model. The basic assumption of the model is that passengers know in advance, which parts of the network will be congested. Passengers take the possibility of failure to board a vehicle into account before they start their journey. In the model passengers use strategies instead of routes. A framework for strategy costs is developed, which is based on random variables. This way it is possible for the first time to take into account the passenger's averseness to travel time variability in a public transport assignment model. Furthermore, strategy cost functions are developed that reflect limited information and bounded rationality of passengers. Finally, cost functions that reflect the use of portable journey planners are analyzed. The assignment model is analyzed in detail on a small bottleneck network. The results show that the model reacts as expected in all cases. In the model the peak of passenger arrival times on the origin stop is earlier if there is more demand, which is a result that is hard to reproduce in models that do not have explicit capacity constraints. An improved method to model demand is developed. Instead of the original demand model, which is based on grouping passengers into groups before the strategy choice is executed, strategy costs are calculated first, and then strategy choice is executed. As opposed to the original model this method does not suffer from a discretization error and leads to stable results.

The management of waste biomass is an increasing problem. The high water content and mixed composition make its wider utilisation difficult. In addition, there are certain invasive species of flora in the UK which cause significant damage to the natural and built environment. One of the most publicised and problematic species is Japanese Knotweed (Fallopia japonica) or JKW. There is a growing recognition that global resources are being consumed at an increasing rate that is not sustainable for the long-term stability of our society. One such commodity material is activated carbon, which is mostly made from coal and imported to the UK in significant quantities (16,000 tonnes per annum). Thus, this research has focussed on investigating the feasibility of utilising waste biomass as a potentially novel and renewable source of activated carbon. This research required the characterising and assessment of the suitability of green (biomass) waste and JKW as potential feedstock for the production of activated carbon. The JKW biomass was separated into rhizomes (JKWR) and stems (JKWS) and experiments were conducted independently. Some of the characterisation tests conducted included CHNS analysis, thermal degradation behaviour and lignocellulosic content analyses. Using high temperature carbonisation and steam activation, waste biomass was converted into activated carbon. For the purpose of this work, the parameters that were investigated were activation temperature, time and water flow rate. The resulting adsorbents were characterised using established international as well as peer-reviewed methods in order to determine their capabilities as activated carbons. These included BET surface area measurement, butane working capacity, phenol adsorption tests as well as iodine number determination. Green waste was not suitable to undergo steam activation as it had high ash content and low carbon content. As a result, the research focussed on the carbonisation and subsequent steam activation of JKW. JKW biomass was carbonised at 600°C for 1h and the JKW chars were activated under optimised conditions at 925°C for 1h under 0.5ml/min water flow rate. BET surface areas in excess of 900m2/g were achieved and this compared very favourably with a benchmark international commercial carbon, Filtrasorb 400. It was observed that increased steam activation temperatures resulted in activated carbons with high degrees of microporosity and the relative microporosity decreased with activation temperature. The carbons were also superior to Filtrasorb 400 in phenol and iodine adsorption tests. Further, Langmuir phenol adsorption capacities of 256 mg/g and 222 mg/g and iodine numbers of 1307 mg/g and 1190 mg/g, respectively were measured for JKWS and JKWR carbons. There are growing concerns over new water pollutants which arise from plastic use. These molecules are known to exhibit oestrogenic activity and hence, their removal is becoming a priority. The application of these carbons for this purpose was tested, using bisphenol-A (BPA) as a surrogate chemical of interest. JKWS activated carbon was able to perform as well as Filtrasorb 400 in BPA adsorption tests achieving at least 300 mg/g capacity, which is extremely promising for a novel, biomass derived activated carbon. Overall, this research work has clearly demonstrated that rather than regarding waste biomass, and particularly Japanese knotweed, as a problem, it may be an opportunity to provide the UK with a home-sourced and renewable feedstock for commercial activated carbon. Adopting this feedstock would be a major step towards resolving two UK government goals; reducing waste arisings and creating a more sustainable economy by reducing demand for imported products.

This thesis investigates two fundamental technological challenges that prevent water utilities from deploying infrastructure monitoring apparatus with high spatial and temporal resolution: providing sufficient power for sensor nodes by increasing the power output from a vibration-driven energy harvester based on piezoelectric transduction, and the processing and storage of large volumes of data resulting from the increased level of pressure and flow rate monitoring. Piezoelectric energy harvesting from flow-induced vibrations within a water main represents a potential source of power to supply a sensor node capable of taking high- frequency measurements. A main factor limiting the amount of power from a piezoelectric device is the damping force that can be achieved. Electronic interface circuits can modify this damping in order to increase the power output to a reasonable level. A unified analytical framework was developed to compare circuits able to do this in terms of their power output. A new circuit is presented that out-performs existing circuits by a factor of 2, which is verified experimentally. The second problem concerns the management of large data sets arising from resolving challenges with the provision of power to sensor devices. The ability to process large data volumes is limited by the throughput of storage devices. For scientists to execute queries in a timely manner, query execution must be performant. The large volume of data that must be gathered to extract information from historic trends mandates a scalable approach. A scalable, durable storage and query execution framework is presented that is able to significantly improve the execution time of user-defined queries. A prototype database was implemented and validated on a cluster of commodity servers using live data gathered from a London pumping station and transmission mains. Benchmark results and reliability tests are included that demonstrate a significant improvement in performance over a traditional database architecture for a range of frequently-used operations, with many queries returning results near-instantaneously.

Construction of underground structures in urban areas requires a detailed assessment of the associated movements imposed on adjacent structures and services and in particular of any damage that may be caused. The most efficient way of investigating these issues is through the application of advanced numerical analysis, using for instance the finite element method. However, for a useful analysis to be performed, a high quality ground investigation must be conducted in order to derive the necessary soil parameters for numerical modelling. This thesis focuses particularly on the case study of the Ivens shaft located near to the Baixa-Chiado station of the Lisbon Metro, Portugal. This is an underground structure of a complex shape and significant depth, situated in the centre of the city and it is therefore important to assess the influence of its construction on the existing adjacent structures and services. In the first part of the thesis the results of the geotechnical survey performed on the relevant Miocene formations located at the Ivens shaft site are presented and discussed. In particular, the “Areolas de Estefânia” formation was characterised in detail since this layer had not sustained significant investigation in the past, mainly due to difficulties in sampling. From the extensive characterisation undertaken, which included both field and advanced laboratory tests, it was possible to derive a suitable framework for the different formations in terms of strength and stiffness. Such information was then used to calibrate appropriate soil constitutive models for use in the numerical analyses. In this respect, the new generation of algorithms, known as Genetic Algorithms, was employed to increase the efficiency and accuracy of the calibration procedure. The second part of the thesis focuses on the 3D numerical modelling of the excavation of the Ivens shaft, which was performed employing the state-of-the-art software ICFEP (Imperial College Finite Element Program). The results obtained permitted the quantification of the shaft and ground movements and their effect on adjacent structures. Particular attention was given to the influence of the excavation on the Baixa-Chiado station and on the adjacent buildings founded near the ground surface. Finally, a parametric study was carried out in order to investigate a number of shaft parameters that may affect the movements and to provide more general guidance for shaft construction.

Portland cement (PC) is a fundamental component of the construction industry. However, its manufacturing process is responsible for ~5 % of global anthropogenic CO2 emissions. Given current demand for PC which is expected to triple by 2050, there is an urgent need for the production of alternative binders with a lower carbon footprint. One type of such alternative binder are magnesium oxide (MgO) based cements. This research has investigated the properties of three novel magnesium oxide based cement systems as potential binders that could be used for some standard cement applications. Previous research at Imperial College London found that the addition of a hydrated magnesium carbonate to MgO prior to hydration resulted in the production of setting and strength gaining samples. One of the main objectives of this research was to understand how the addition of magnesium carbonate gave the system cement-like properties and to investigate the types of strength possible from a basic system as well as to identify the main parameters that affect strength, thus allowing for future optimisation. It was found that the presence of carbonate and its effect upon the system pH alters the type of Mg(OH)2 formed, giving a more stable microstructure that accounts for the strengths achieved. The type of MgO was found to be an important parameter, as was particle size. Due to water demand, a 10 % carbonate – 90 % MgO mix was chosen as the optimum mix. The second system studied was the silica (SiO2) – MgO system. This was investigated in order to assess the potential of the reaction between MgO and silica to form M-S-H gel and to study the mechanism of formation of reaction products. It was found that reactive MgO and amorphous silica can react together upon hydration to form a mixture of M-S-H gel and Mg(OH)2, dependent upon the SiO2/MgO ratio. These systems have considerable compressive strengths the extent of which depends upon the type of silica. An optimum mix of 30 % silica – 70 % MgO (by dry weight) was found Finally, a simple ternary system of magnesium carbonate - silica - MgO was investigated in order to assess if the presence of the combination of both ‘additives’ could create a better system than either of the two-component systems. Strength results suggested that there is no added benefit to the system in combining the two-component systems. For all three systems studied, the high w/s ratios required were found to be a significant limiting factor.

A musculoskeletal model of the lower limb has been implemented and assessed in order to be used as a predictive tool to quantify the hip contact force (HCF) vector acting between the femoral head and the pelvic acetabulum. The model is based on a published anatomical dataset, which has been critically revised and extended. The HCFs obtained through the model have been assessed at multiple levels of detail against measurements from instrumented prostheses from a publicly available dataset. In the first instance, a direct comparison has been undertaken in order to verify predicted HCF magnitudes close to the measured and muscle recruitment consistent with electromyographic activation profiles reported in the literature. Secondly, a trend validation was performed to ensure the correct behaviour of the model when the same daily living task (level walking) was performed with different modalities. Finally, a falsification of the model was performed by challenging it to predict the exact components of the measured hip contact forces for both level walking and stair climbing. The closest achievable predictions were also calculated, together with the accuracy of a conventional use of the model not exploiting a priori knowledge of the joint contact forces. Once the assessment of the model was completed, a dataset of anthropometric, kinematic and kinetic data was collected on eight young healthy subjects performing daily living activities. As a demonstration of the potential use of the dataset, a subject specific model was generated and used to estimate HCF direction and magnitude for level walking and stair climbing, the same activities investigated during model validation. The model was further extended in order to include the upper part of the body and potentially analyze full body kinematics and kinetics. A further modified version of the model was finally developed in order to be used in finite elements analyses or more generally in applications requiring equilibrated sets of muscle and joint forces acting on a bone structure, as the highly discretized representation of the muscles makes the model particularly suitable for this kind of use. The developed model has been implemented in the open source software OpenSim and is freely available for download and use in research.

As part of the continuing effort undertaken at Imperial College London to develop a unified measure of robustness, the current study addresses several issues which were identified in the past as prospective enhancements to the ductility-centred framework. As robustness evaluates the structural performance against extreme local actions, it should consider within the assessment framework the duration of the accidental event and its repercussion on the structural response. In this context, incorporation of rate-sensitivity is a step forward to a more realistic structural assessment under blast/impact loading. Towards this end, the rate-sensitivity of steel is quantified with the aid of experimental coupon tests. Subsequent studies on rate-sensitivity at the structural level, which similarly include validation by component testing under moderate to high rates, address a knowledge gap on the dynamic over-strength and ductility supply associated with sudden column loss scenarios. Further developments are made to the framework in order to accommodate material rate-sensitivity, where a case study is undertaken which illustrates the diminishing rate effects at higher structural levels. Since local damage resulting from extreme loading does not revolve around a single possible damage scenario, it is important to investigate other local damage scenarios besides the typically considered single column removal. In this context, the feasibility and practicality of scenarios involving the simultaneous loss of multiple columns are considered, with generalisation of the simplified dynamic assessment and development of simplified models based on dominant modes of deformation. As the study of different damage scenarios moves the discussion on robustness towards rational risk assessment, this work aims to demonstrate the adequacy of the ductility-centred framework to the quantification of the failure probability under column loss scenarios. With an illustrative application study, it is established that such risk assessment is not only feasible but may ultimately provide a valuable decision-making tool in the design process of robust structures.

As more buyers become interested in the spot purchase of liquefied natural gas (LNG), the share of spot trade in LNG business increases. This means that the cash flowing into the upstream of LNG projects is a combination of that generated by deliveries to long-term contract (LTC) customers and uncommitted product and arbitrage spot sales. LTC cash flows are more predictable while uncommitted product and arbitrage cash flows, affected by the dynamics of supply and demand, are more volatile and therefore less predictable. In this research, we formulate an inventory routing problem (IRP) which maximizes the profit of an LNG producer with respect to uncommitted product and arbitrage spot sales, and also LTC deliveries at an operational level. Using the model, the importance of arbitrage, interest rates and compounding frequency in profit maximization, and also the significance of interest rates and fluctuation in spot prices in decision-making for spot sales of uncommitted product are studied. It is proven that writing traditional LTCs with relaxed destination clauses which assist in arbitrage is beneficial to the LNG producer. However, in contrast to what was predicted neither the interest rate nor the compounding frequency has any importance in profit maximization when no change of selling strategy is observed. Apart from these, it is shown that there is a trade-off between the expectation of higher spot prices and the inventory and shipping costs in decision-making for spot sales of uncommitted product in the LNG industry. Finally, it is observed that the interest rate can affect the set of decisions on spot sales of uncommitted product, although the importance of such changes in profit remains to be further explored.