The topic of this thesis is the investigation of the structural behaviour of cold-formed steel flooring and purlin systems, taking into consideration the beneficial effect of interaction between structural components. Experiments have been conducted on flooring systems comprising cold-formed steel joists and wood-based particle boards, considering the typical screw fixings employed in current practice as well as alternative means of shear connection. The experimental findings showed that mobilisation of composite action within this type of system, through enhancement, beyond that currently used, of the employed shear connection, is feasible, bringing corresponding increases in capacity and stiffness. In order for the influence of the key parameters to be further examined, a finite element model simulating the examined systems has been developed, validated and employed for parametric studies. Analyses confirmed the experimental findings, showing that significant benefits in terms of capacity and stiffness can be achieved, especially for systems comprising thinner steel sections. Based on the obtained experimental and numerical results, a full design method, following the fundamental concepts of current design codes for composite structures, has been devised, providing accurate predictions of moment capacity and flexural stiffness. Finally, a numerical investigation has been performed on continuous two-span roof systems comprising cold-formed steel purlins, accounting for their interaction with the corrugated sheeting. The study showed that moment redistribution is possible within these systems, but usually accompanied by a reduction of the moment capacity of the central support. A previously devised method for the design of continuous purlin systems, making direct use of cross-section capacities at key locations, together with a factor to allow for the fall-off in moment at the central support, has been assessed and advanced.

Stiffness reduction offers a practical means of considering the detrimental influence of imperfections and the spread of plasticity on the strength and stability of steel structures. In this thesis, a stiffness reduction approach for structural steel design is presented. The proposed method is carried out by reducing the stiffness of steel members through developed stiffness reduction functions and performing Linear Buckling Analysis (LBA-SR) and Geometrically Nonlinear Analysis (GNA-SR). Since the deleterious influence of geometrical imperfections, residual stresses and the spread of plasticity is fully taken into account through the developed stiffness reduction functions, the proposed design approach does not require the use of member design equations, but only requires cross-section checks, thus leading to practical design. Finite element models of steel members and frames are created and validated using experimental results from the literature. Geometrically and Materially Nonlinear Analyses (GMNIA) of the validated finite element models are used to verify the proposed stiffness reduction method in all considered cases. The proposed stiffness reduction method is initially developed for the flexural buckling assessment of columns and the in-plane design of beam-columns, where a stiffness reduction function is derived using the European column buckling curves, providing the same strength predictions as determined through these curves. The proposed method is then extended to the lateral-torsional buckling assessment of steel beams and the flexural-torsional buckling assessment of steel beam-columns. Having established its validity for individual members, the proposed method is applied to steel frames. Both non-redundant and redundant benchmark frames from the literature are considered. It is observed that the proposed stiffness reduction method provides a reliable and accurate design approach.

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The ultimate strength of reinforced concrete beams of both rectangular and tee section under the combined effect of bending and shear forms the topic of this investigation. The published results of tests on over 1000 rectangular and tee beams have been collected and the ultimate strength of each of them predicted from an empirical formula. The overall coefficient of variation of the ratio of predicted to observed strengths is found to be about 18%. By simulating the anticipated variations in the parameters of the empirical formula it has been shown that the overall variation in the results is not excessive. Over 200 new tests on beams of reinforced plaster both rectangular and tee sections, and also the previously published test results on plaster beams support the general form of the empirical formula. Fourteen new tests on reinforced concrete tee beams with short shear spans indicate that the behaviour of such tee beams can be predicted as confidently as that of rectangular beams. The proposed empirical formula will successfully predict the strength of beams tested in the restrained condition and also under uniform load. This is supported by further tests on reinforced plaster beams. The mechanism of shear in reinforced concrete beams is explained by quoting the test results of other investigators and also by the present tests on plaster beams. It will be shown that bond between the reinforcement and concrete is a fundamental factor which influences shear failures. The load factors of the simply supported beams implied by the shear clauses in the current British Code, the current American Code and also by the proposed British Code are compared. The reliability of such predictions is examined. The economic design of reinforced concrete beams is examined by different approaches and the cost is compared. It is suggested that the cost of shear reinforcement is a very small part of the total cost of such beams.

Geological repositories are being considered as the best feasible solution for the storage of hazardous materials such as high level nuclear waste throughout the world, including the UK. However; when crystalline rock is the chosen storage medium, the construction of the underground tunnels and caverns can enhance discontinuities within the rock. These discontinuities can be pathways by which radio-nuclides can reach the biosphere, due to their higher permeability, connectivity and density (Blyth and Freitas, 1992). Thus, depending on aperture, density and predicted travel times, it may be necessary to grout all fractures, even small aperture ones, which over thousands of years can contribute significantly to subsurface flow. Conventional cementitious and chemical grouts are unsuitable within some regions of a geological disposal facility due to concerns regarding longevity, toxicity, reactions with other barriers and/or workability issues. The four main requirements of a grout are; to be of low viscosity as the lower the viscosity the easier it is to achieve good penetration, to have a controllable gel/setting time, to be chemically inert to prevent reactions within the subsurface or have any toxic consequences during preparation, and to be durable thus able to withstand exposure to varying physic-chemical condition. MICP (Microbially Induced Calcite Precipitation) and Colloidal Silica are novel grouts which may be suitable for the sealing of fine aperture fractures in rock. MICP research has been predominantly focussed on its application in sediments, whilst colloidal silica has shown its potential for reducing the liquefaction potential of non-cohesive soils and for sealing fractures. This research examines the influence of hydraulic controls (velocity, flow rate, aperture) on the spatial distribution of microbially induced calcite precipitation (MICP) within simulated fractures using flocculated Sporosarcina pasteurii. The experimental results show that under flowing conditions, the spatial distribution of microbially induced calcite precipitate on fracture surfaces is controlled by fluid velocity. Even for a uniform initial fracture aperture with a steady flow rate, a feedback mechanism existed between velocity and precipitation that resulted in a precipitate distribution that focussed flow into a small number of self-organizing channels which remained stable. Ultimately, this feedback mechanism controlled the final aperture profile which governed flow within the fracture. To use MICP for field scale sealing operations (e.g., in aquifers and host rock surrounding nuclear waste storage sites), it is important to develop an injection strategy that ensures microbially precipitated calcite is distributed homogenously throughout the rock body to avoid preferential flow through high porosity pathways. Sporosarcina pasteurii was found to be able to hydrolyse urea for several days before the bacteria became encased within calcite preventing access to the cementing fluid. The higher rates of urea hydrolysis occurred within the first 9 hours, though significant rates of urea hydrolysis still occurred after this period. By reducing the size of bacterial flocs it is possible to reduce the impact of sedimentation and straining, promoting a more even distribution of bacteria thus calcite precipitate throughout the plate. By increasing the length of time that the bacteria flow through the fracture, more bacteria can become entrained upon the fracture surface giving a better distribution. The introduction of a filler (colloidal silica) that can also act as a nucleation site for calcite precipitation was examined as a way of reducing the time it takes for the sealing of a fracture. Both Sporosarcina pasteurii and colloidal silica have negative surface charges thus colloidal silica could be used as a nucleation surface, this plus its nanometre size which could allow for a better distribution of and could enhance calcite precipitation. A clear difference in the mass of grout retained within the fracture was seen, with MICP alone showing the greatest weight increase. During the 8 grouting cycles with MICP + colloidal silica there appeared to be pieces of calcite travelling through the open channels. This would indicate that the calcite is unable to attach to the fracture surface. Thus, adding a small amount of colloidal silica to the cementing solution as a filler was not an efficient way to produce calcite fill. However, Sporosarcina pasteurii produces ammonium ions from the hydrolysis of the non-ionic urea, which as a cation can destabilise the silica sol resulting in gelation. Batch tests were used to determine what differences in gel point, gel rate and shear strength were created by different cations, including the chemical addition of ammonium ions and the biological production of ammonium ions by the bacterium Sporosarcina pasteurii. The sensitivity of colloidal silica to calcium chloride can result in dramatic differences in gel time with small changes in molarity having great impact on whether the colloidal silica gels or not. The direct addition of ammonium salts requires ten times the concentration, compared to CaCl2, to achieve similar shear strength values. However; this concentration produces very short gel times, potentially reducing the radius of penetration. The bacterial in-situ production of ammonium ions gives the greatest gel times yet still produces the same shear strength as that of a sodium chloride accelerator. This increasing of gel times, without adversely impacting grout properties, could be beneficial for penetrating greater distances into fractured rock reducing the number of injection points required. This would be particularly useful for subsurface engineering applications where large volumes of rock are required to be grouted.

Natural methane hydrate soil sediments attract worldwide interest, as there is huge commercial potential in the immense global deposits of methane hydrate that lies under deep seabeds and permafrost regions. Methane hydrate develops and exists in the pores of soil sediments under the conditions of high pressure and low temperature. The methane hydrate-bearing sediment can be exploited to extract methane gas, as methane gas is the predominant element of natural gas. However, the sediment’s geomechanical behaviour is poorly understood, but it has impacts on geotechnical issues, such as the instability of the seabed sediment layers and wellbore collapse, and it may also cause various negative environmental effects, particularly in regards to the exploration and exploitation process. Hence, further scientific research is needed. Due to the limitations of in-situ and laboratory studies, in this PhD research, a numerical method Discrete Element Method (DEM) was employed to provide a unique particle-scale insight into the granular geomechanical behaviours of hydrate-bearing sediment. A comprehensive DEM research was performed in order to simulate two commonly used geomechanical investigation methods employed in hydrate-related studies: the triaxial compression test and seismic wave propagation. Accordingly, the six major contributions of this DEM research are: (1) two typical types of microscopic hydrate distribution patterns within soil pores were investigated via a consistent basic soil model: the pore-filling hydrate pattern and the cementation hydrate pattern; (2) The large-strain deformation and the critical state behaviours were explored; (3) a wave propagation study was performed using the DEM hydrate-bearing sediment samples; (4) the bonding strength effect in the cementation model was systematically discussed; (5) the effect of elongated soil particles on the geomechanical behaviours of sediments was studied; and most importantly (6) a comprehensive particle-scale microscopic analysis was conducted to assist the interpretation of the macro responses in the in-situ, laboratory and numerical studies.

This study was carried out to enhance the durability of concrete exposed to chloride attack by means of two approaches: (i) to design sustainable concrete compositions and (ii) to apply suitable maintenance techniques consisting of electrochemical chloride extraction (ECE) and surface coating (SC) treatments. Subsequently, the study was divided into two separate phases for this study. The first phase was to assess the role of the cement combinations on enhancing chloride resistance of concrete. The cement combinations composed of, Portland cement (PC)/fly ash (FA) and PC/ground granulated blast furnace slag (GGBS) in binary mixes, and with silica fume (SF), metakaolin (MK) and limestone (LS) as addition to form ternary concretes. The w/c ratio of concrete was selected in the range of 0.35 to 0.45 for the requirement of high performance. To improve the degree of accuracy, four contemporary chloride test methods were used in this work to measure the chloride penetration of concrete, which are: (i) Method A-rapid chloride permeability test to ASTM C1202; (ii) Method B-chloride migration test to NT Build 492; (iii) Method C-Multi-Regime test to UNE 83987:2009; and (iv) Method D-chloride diffusion test to CEN/TS 12390-11. The variability of different methods was evaluated and the correlation between them discussed. In addition, the microstructure and chloride binding capacity of relevant cement paste were investigated in order to provide more information for assessing the improvement on chloride resistance of different binary/ternary mixes. The results indicated that the chloride resistance of concrete was benefited significantly when blended with additional cement combinations. The concrete blended with FA or FA/LS showed no contribution on improving chloride resistance before the age of 28 days, but significant improvement up to age of 90 days. Compared to 100PC concrete at the equal w/c ratio, generally, it demonstrated 3-7 times decrease of the chloride durability indicators in the binary and ternary concrete. When comparison was conducted at equal strength grades (45, 55, and 65 N/mm2), the improvement on the chloride durability was more significant in the binary and ternary concrete. However, for individual binary or ternary concrete, the decrease in w/c ratio from 0.45 to 0.35 did not cause significant expected reduction in the chloride diffusion coefficient, especially when w/c ratio went down below 0.4. This was mainly attributed to the reduction of chloride binding capacity (loss of accessible binding sites to chlorides) of concrete caused by decreasing w/c ratio, although which still can refine the pore structure of concrete. The maintenance approach is necessary and inevitable when the chloride durability of designed concrete is insufficient to satisfy the designed working life. The second phase investigated the application of suitable maintenance approach involving ECE and SC treatment on the chloride contaminated concrete prior to the corrosion of embedded steel. The selected specimens were 100PC, 70PC30FA and 50PC50GGBS concrete with w/c ratio of 0.35, 0.45 and 0.55. Chloride was driven into 28-day concrete under the migration test rather than mixing at time of casting concrete. Two cycles of ECE process were applied on concrete, and then the pore structure characteristics and carbonation resistance of concrete were measured. Those specimens, including reference concrete, desalinated concrete and desalinated concrete coated with coating materials (Silane and RheoFIT®790) were placed into the artificial spraying salt solution of 1.0 mole/litre concentration for 30 days. The chloride content profile of sprayed specimens were obtained, and used to calculate the chloride diffusion coefficient based on three different calculation methods. The observations stated that approximately 65% of penetrated chloride was extracted during two cycles of ECE treatment for 100PC and 70PC30FA concrete, and about 57% for the 50PC50GGBS concrete. The ECE treatment increased the porosity of all mixes due to movement of ions and dissolution of solid phase in concrete, while much more significant in 50PC50GGBS concrete than 100PC and 70PC30FA concrete. It also reduced significantly the carbonation resistance of concrete at early exposure time (before 6 weeks), but insignificantly up to 10 weeks exposure period. Additionally, it showed significant increase of chloride diffusion coefficient in the desalinated 50PC50GGBS concrete compared to the non-desalinated concrete. However, the influence of chloride diffusion coefficient was not significant in the desalinated 100PC and 70PC30FA concrete. Coating materials performed effectively on preventing chloride ingress from a spraying environment according to the comparison of chloride profile between coated and uncoated specimens, except for the RheoFIT®790 coated on 100PC concrete. Based on the current calculation methods for the chloride profile, the calculated chloride diffusion coefficient of coated concrete also demonstrated significant reduction compared to those uncoated concrete. Finally, the predicted service life of concrete after ECE and SC treatment demonstrated long extended life for 70PC30FA concrete, where only ECE treatment can increase total service life by 47%-66%. Both ECE and SC (Silane with 50 years working life) treatments will extend total service life to maximum 1.9-2.5 times, and minimum 1.7-2.0 times. The extended service life is highly related to the working life of coating materials. However, for 50PC50GGBS concrete (with increasing chloride diffusion coefficient caused by ECE treatment), only 3%-4% increase of the total service life was found due to the ECE treatment. Both ECE and SC (Silane with 50 years working life) treatments can offer extension of service life to maximum of 1.3-2.2 times, and minimum of 1.2-1.3 times.

This thesis investigates the three-dimensional container loading problem. We review all literatures published in this area, and explain our unique problem raised from an industry partner. As constructive heuristic remains uncontrollable to us, we design improvement algorithms both to and not to intervene with how constructive heuristic works, namely iterated local search and beam search. New benchmark data sets for multiple containers problem are generated to fill the shortage of challenging data sets. Computational results for homogeneous containers problem indicate that while both approaches work on our problem, beam search remains a favourable choice. We also extend our algorithms to solve heterogeneous containers problem.

This study presents an experimental and numerical contribution to the understanding of the structural behaviour of slabs and beams made of ultra-high performance fibre-reinforced concrete (UHPFRC). One of the main factors affecting the use of UHPFRC in major construction projects is not having an accepted design method due to the lack of understanding of the structural behaviour of this material, especially for slabs. Therefore, a major part of this thesis focuses on the static flexural behaviour of slabs. A novel experimental technique is developed and employed within an extensive series of experiments to better understand the structural behaviour of UHPFRC. Tests are conducted on one-way and two-way slabs with both fully fixed (FF) and simply supported (SS) boundary conditions; these are of interest in structural applications such as bridge decks and the floors of buildings. Details of tests conducted on 660 mm square slabs with thicknesses of 25, 35, 45 and 60 mm are presented. The effect of geometries on steel fibre distribution in the UHPFRC specimens was investigated using physical fibre counting at the location of the cracks. It was found that the fibre distribution and orientation changes as the specimen size changes. Moreover, the number of fibres that bridged between the two cracked faces reduced as the specimen thickness increased. A numerical model using advanced finite element modelling techniques in ABAQUS is also presented. A nonlinear concrete damage plasticity (CDP) model is used for the simulation and it was found to agree well with the experimental results in terms of load-displacement behaviour of statically indeterminate UHPFRC slabs. In addition, the model was also found to accurately capture the peak-load carrying capacity of the slab specimens. Parametric studies were carried out for slabs with thicknesses up to 120 mm. The experimental results confirmed the reliability and accuracy of the FE modelling. The numerical model was further validated by the uniaxial tensile and compressive data and it was found that the model accurately reproduced the material properties behaviour. The thesis also includes an investigation of size effect on the structural strength of UHPFRC elements. This concerns the static flexural behaviour of similar notched UHPFRC beams with various depths under a three-point bending test and the prediction of load-crack mouth opening displacement (CMOD) behaviour. Nonlinear finite element simulations using the CDP model were also conducted and it was found the model can predict full load-CMOD curves, peak-load and crack propagation processes with good agreement with experimental data. Furthermore, a parametric study considering larger sizes of specimens up to a depth of 300 mm was carried out and it was found that the size effect on the beam’s nominal strength is negligible due to the relatively high ductility of UHPFRC compared to other types of concrete.

This Engineering Doctorate thesis summarises the research conducted at the Applied Mechanics Division, UMIST and Reverse Engineering limited (REL), the sponsoring company, from 1994 to 1999 on the analysis of concrete structures. With the advent of numerical techniques such as finite element analysis being used to analyse complex structural behaviours, this research investigated the post yield behaviour of concrete structures subject to demolition using a Natural Draught Cooling Tower (NDCT). Both implicit and explicit integration schemes were used to assess the response of the structure to buckling and collapse respectively. A review of demolition techniques was carried out including collapse analysis of an eight storey composite concrete-steel building. The aim of the research was to investigate various engineering aspects, both experimental and numerical, and bring closer to industry recommendations for further investigation.