The UK has a long history in the railway industry with a large number of railway assets. Railway bridges form one of the major asset groups with more than 35,000 bridges. The majority of the bridge population are old being constructed over 100 years ago. Many of the bridges were not designed to meet the current network demand. With an expected increasing rate of deterioration due to the increasing traffic loads and intensities, the management authorities are faced with the difficult task of keeping the bridge in an acceptable condition with the constraint budget and minimum service disruptions. Modelling tools with higher complexity are required to model the degradation of assets and the effects of different maintenance strategies, in order to support the management decision making process. This research aims to address the deficiencies of the current bridge condition systems and bridge models reported in the literature and to demonstrate a complete modelling approach to bridge asset management. The degradation process of a bridge element is studied using the historical maintenance data where previous maintenance actions were triggered by a certain type of defects. Two bridge models are then developed accounting for the degradation distributions, service and inspection frequency, repair delay time and different repair strategies. The models provide a mean of predicting the asset future condition as well as investigating the effects of different maintenance strategies will have on a particular asset. The first model is a continuous-time Markov bridge model and is considered more complex than other models in the literature, the model demonstrates the advantages of the Markov modelling technique as well as highlighting its limitations. The second bridge model presented a novel Petri-Net modelling approach to bridge asset modelling. This stochastic modelling technique allows much more detail modelling of bridge components, considering: non-constant deterioration rates; protective coating modelling; limits of the number of repairs can be carried out; and the flexibility of the model allows easily extension to the model or the number of components modelled. By applying the two models on the same asset, a comparison can be made and the results further confirm the validations and improvements of the presented Petri-Net approach. Finally, optimisation technique (Genetic Algorithm) is applied to the bridge models to find the optimum maintenance strategies in which the objectives are to minimise the whole life cycle cost whist maximising the asset average condition. A hybrid optimisation that takes advantage of both bridge models, resulting in a significant time saving, is also presented.

The buffeting response is a type of vibration caused by wind turbulence. As the bridge span and structural complexity increase, this kind of response is notable. Therefore more accurate analysis simulation methods are needed to investigate this aerodynamic phenomenon. The aim of this thesis is to review, discuss and compare the different bridge buffeting simulation approaches in the frequency domain and find the possibility of Computational Fluid Dynamic (CFD) method application in bridge buffeting prediction. In this thesis, the conventional bridge buffeting statistical analysis methods considering the influence of different parameters such as mode coupling, self-excited forces and aerodynamic admittance on the simulation results are firstly reviewed and compared. Since wind turbulence may not excite all structural vibration modes in some frequency ranges, an alternative approach based on the Proper Orthogonal Decomposition (POD) is proposed to study the effective turbulence contribution to the structural vibration. However due to the complexity of turbulence, quasi-steady theory is widely adopted and some semi-empirical functions such as aerodynamic admittance, joint acceptance are introduced to simplify the simulation. With the development of CFD method, CFD simulation of bridge aerodynamic phenomena has become possible. Since the bridge buffeting response is induced by wind turbulence, it is very important to capture the time varying characteristics of wind turbulence. In CFD technique, to close the Navier-Stokes equations and reflect unsteady characteristics, turbulence modelling is always adopted. At present Direct Numerical Simulation (DNS) is an accurate model to capture the time variation unsteady characteristic of the wind turbulence. However, the problems of civil engineering are always high Reynolds numbers, which make the simulation of aerodynamic phenomena of civil engineering impractical based on DNS method. Therefore an alternative model, known as Large Eddy Simulation (LES), becomes popular. In this thesis an unsteady inlet boundary generation technique based on an Autoregressive Moving Average (ARMA) model is proposed to simulate the unsteady inflow turbulence. 3D LES will be selected to validate the applicability of this model in the prediction of the unsteady characteristic of buffeting simulation by investigating the flow characteristic around a square cylinder under different mesh density and different LES model such as standard LES model, dynamic LES model and WALE model at Reynolds number 13,000. Before comparing the influence of inflow boundary condition with turbulence intensity (5%) on the flow around a square cylinder, an empty domain is selected to validate current inflow turbulence generation technique. Major steps of Fluid Structure Interaction (FSI), suitable for future simulation of bridge structural buffeting response, are proposed to predict the structural buffeting response induced by the inflow turbulence. To test the propose procedure of FSI, a square cylinder will be used, the across-flow oscillation of square cylinder with constant damping ratio will be considered to investigate the influence of steady inlet boundary condition and unsteady one on the response of structure. In addition different LES models are considered to compare their influence on the response of square cylinder.

This thesis reports the findings of an investigation into the feasibility of using vibration characteristics to monitor the structural health of bridges. The study is the second part of a larger project commissioned by the UK Highways Agency into the investigation of possible monitoring methods that can be used in a pass/fail/monitor inspection programme. To this end, ten one-quarter-scale 5m span reinforced concrete bridge decks were fabricated and loaded incrementally to failure in the laboratory. The dynamic properties of the decks were investigated at each of the loading increments to evaluate their sensitivity to structural cracking using both free and forced vibration. The results indicated that, for the specimens tested, natural frequencies were, in general, more sensitive to the damage introduced than mode shapes. It was found that the support conditions affected the dynamic behaviour of the decks, and indeterminate boundary conditions caused significant variation in the vibration characteristics. This presented several problems in the analysis of the modal properties and, when combined with the damage introduced through static loading, caused some modes to disappear and new modes to be measured, whilst a number of modes also displayed an increase in natural frequency. The application of finite element model updating to determine reduction in flexural stiffness in the damaged areas of the deck provided a systematic method to investigate the condition of the deck. Updating was performed based on the natural frequencies of one symmetrically and one asymmetrically loaded deck, and the cracking observed under the loading, and offered results consistent with expectations. In summary, the evidence presented in this thesis suggests that the natural frequencies of the decks are, in general, more sensitive to the damage introduced than the mode shapes and consistent trends can be observed in the natural frequency change as the damage to the deck increases. However, the application of this method to indicate the structural condition of real bridges may be limited without further investigation as the vibration characteristics were affected by a number of factors arising from the realistic nature of the specimen, such as the three-dimensional distribution of the damage and the indeterminate nature of the support conditions.

It has been two decades since Ultra High Performance Fibre Reinforced Concrete (UHPFRC) has come to the market and, so far, it has been used in only a limited number of highway bridge structures. This is due to many unanswered questions related to its structural behaviour for highway bridge structures and its high initial cost. The lack of knowledge regarding the structural behaviour is down to unavailability of appropriate test methods for this special type of concrete which behaves differently compared to normal concrete. Furthermore, the current precast production contributes to its high initial cost significantly. Therefore, this study has investigated various aspects that are restricting the potential use of UHPFRC for highway bridge applications. The investigation included extensive experimental studies and numerical modelling. In the experimental programme, various parameters ranging from material and mechanical properties, potential use of the concrete for cast in-situ applications to ductility behaviour were investigated. Furthermore, the numerical analyses were carried out to identify appropriate finite element models to predict the flexural and shear behaviour of the concrete. In the experimental work, simple and reliable test methods for material characterisation were developed. The validity of two non-destructive testing methods in studying the elastic properties of the concrete was confirmed. From this, the UHPFRC constitutive material model was obtained and used in numerical modelling. The reliability of the test methods were established by performing numerous experimental tests and similar results obtained at all times. Furthermore, the suitability of the concrete for cast in-situ applications at various temperatures by monitoring the strength development from an early age (12 hours) up to 360 days were investigated. The results showed significant strength gain of the concrete in both compression and tension within 7 days when cured at temperatures similar to site conditions (20 and 30 oC). A phenomenon related to the 90 oC curing temperature in precast production was reported and showed to have caused loss of flexural strength and toughness of the concrete. In addition, for the first time, an effective test method for studying the punching shear strength of the concrete with minimal influence of flexural stress was developed and used successfully. The results showed a reduced effective punching shear perimeter of UHPFRC slabs by half compared to normal concrete. The numerical analyses were carried out using the Abaqus finite element software. In this study, the Concrete Damaged Plasticity (CDP) and Concrete Smeared Cracking (CSC) material models with minor modifications were used to simulate the flexural and shear behaviour of UHPFRC beam and slab specimens, respectively. The results obtained here were validated against experimental studies with good agreement. The CDP model was found to replicate the linear and nonlinear structural response of the concrete with better accuracies than the CSC model. This study presents significant findings on the suitability of UHPFRC for structural applications with a lower initial cost compared to its current precast production. Furthermore, results obtained on its excellent structural behaviour in flexure and shear provides structural designers great confidence in using this concrete for highway bridge applications. The findings reported in this study contribute to the literature of UHPFRC significantly.

A number of artificially generated earthquake time-histories (AGETH) fitting to a Eurocode 8 (EC8) response spectrum are randomly generated using SIMQKE software and the average generated spectrum compares well with the EC8 one. Two Finite element (FE) smeared crack models, named Multi-crack and Craft, are well validated against experimental data of concrete and Reinforced concrete (RC) structures under monotonic and cyclic loadings. They are then used in the analysis of RC bridge piers under the AGETH. Several techniques including Fourier analysis, normalised cumulative spectrum, energy dissipation, damage index as well as probability applications are applied to quantify the structural response and damage. Based on the convergence of the representative responses under different numbers of AGETH, a minimum representative number of AGETH from 6 to 11 may be sufficient depending on the confidence band width from the mean of all damage responses. Effects of several parameters of the earthquake and structure to the dynamic response and damage of the bridge pier are investigated. Throughout these parametric studies, several of the common circumstances that structural engineers face are addressed and the proposed number of artificial earthquake time-histories required for non-linear dynamic analysis is thereby validated.

Accurate inspection data is important for efficient bridge management. Visual inspections play a key role in providing this information, but the reliability of such data has limitations. A range of techniques addressing these limitations are used in other sectors, but not to assist routine visual bridge inspection. Work has been undertaken investigating the feasibility of performing routine visual bridge inspections based on systematically collected images alone. The requirements of such a system are considered and defined. The research demonstrates that more detail can be seen in images at 1-pixel-per-mm than can be seen from 3m, and that images at this resolution can be systematically collected, processed, displayed, and inspected to complete General Inspections with results comparable to traditional routine visual inspections. No existing systems were found to be suitable for routinely providing visual inspection data; consequently a prototype was developed demonstrating the feasibility of the image-based inspection approach. The development considered hardware, image collection methodology, processing, alignment, display and interpretation. Inspectors tested and used the system to perform image-based General Inspections on several bridges. It is concluded that an image­based approach can be used to perform routine visual bridge inspections, with no loss of detail compared to traditional inspections.

It is now well established that there are a wide variety of known EDCs (Endocrine Disrupting Chemicals) in the aquatic environment, which include natural (e.g. oestrogen) and synthetic hormones (e.g. ethinyloestradiol), weak environmental oestrogens (e.g. bisphenol A and nonylphenol) and pesticides, fungicides and herbicides, that are able to alter the physiology of exposed wildlife and humans and have become a focus of increasing concern for human and environmental health over the past two last decades. However, the functional implications and potential significance of these findings has yet to be established. In this thesis, a transgenic fish system approach (using a new plasmid) was employed to investigate the effect pathways of EDCs in fish, using transgenic UAS-GFP zebrafish (Danio rerio) as a model species. One of the most critical steps in this approach is the development of an effective construct for the development of sensitive transgenic zebrafish. The required ERE was cloned and three copies were incorporated into a construct. Three vector systems (pKS+, pCS2+ and pBR322-Tol2) were selected for making new plasmids, and investigated to improve the efficiency for sensitivity and tissue specificity. Three constructs were made and tested progressively in the development process. The plasmids contain three oestrogen response elements (3ERE), a TATA box and GAL4ff. The three constructs, pKS-ERE-Gal4ff, pCS2-ERE-Galf4ff and pBR-Tol2-ERE, were examined by injecting into zebrafish in a transient assay system. The pBR-Tol2-ERE-Gal4ff construct was selected for generating transgenic zebrafish because it showed tissue specific manner (i.e. reduce mosaicism) and Tol2 transposon has the capacity to improving greatly the chances for generating TG fish such as high germline transmission frequency. The construct pBR-Tol2-ERE-Gal4ff required to examine the functional capability of using transient expression assay before generating transgenic fish. The Gal4-UAS/GFP method was adopted and produced a two step amplification of the oestrogenic signal. A novel transient expression assay system was developed using a synthetic oestrogen responsive element, the Tol2 mediated Gal4-UAS systems and the GFP reporter gene, which are responsive to environmental oestrogens using green fluorescent microscopy in zebrafish (Danio rerio) and medaka (Oryzias latipes). The construct worked well and vector system in transient expression assays proved a rapid, sensitive, tissue specific system for the detection of oestrogenic EDCs in both the zebrafish and medaka, indicating the likely wide suitability for application to other fish species. These data indicate that this system would be a particularly powerful technique for use in species with long generation times and/or where there are other difficulties for generating transgenic lines in those species. After the transient expression assay, the construct pBR-Tol2-ERE-Gal4ff with transposase mRNA was co-injected into early one cell stage and bred for 3 months. The embryos were collected from the founders (a male and a female) and exposed to EE2 to identify the transgenic zebrafish. An oestrogen responsive transgenic zebrafish (ERE-TG fish) was established under an oestrogen inducible promoter derived from multiple tandem oestrogen responsive elements. Gal4ff-UAS system was adopted to generate ERE-TG fish to enhance the sensitivity, which has not been used for generating biosensor zebrafish yet. Oestrogen exposures were shown to induce specific GFP expression in the heart, muscle, otic vesicle, brain, neuromasts, eye/ear ganglions and fin, in addition to that in the liver and gonad, which has not been shown previously in other oestrogen responsive transgenic zebrafish, illustrating both the enhanced sensitivity of our detection system and the potential for these tissues as target sites for wider health effects for exposure to environmental oestrogens. Furthermore, oestrogen chemicals are converted to an oestrogenic signal in different tissues preference. Oestrogen receptors (ER α, β1 and β2) morpholinos (MOs) and exposures with oestrogen receptor antagonist were carried out to assess whether the GFP expression was mediated through the ER, regardless of the subtypes. GFP expression was inhibited through injection of the mixture of ERs MOs compared with uninjected transgenic fish larvae. This result indicated that GFP expression was mediated through the ERs. The lowest detectable concentration of EE2, E2, BPA and NP was 1 ngEE2/L, 5 ngE2/L, 100 µgBPA/L and 1 µgNP/L in ERE-TG fish embryos/larvae. These findings provide that ERE-TG fish embryos/larvae systems are useful both for studying physiological mechanisms and for detecting biological target sites of environmental oestrogens. As a preliminary experiment, immature (40 day old) and mature (3 month old) ERE-TG fish were exposed to low concentrations of EE2 for 7 days to prove its potential for developing tissue-specific models of EDCs at different life stages. The lowest detectable EE2 effect concentration was 5 ngEE2/L in the liver and gonad and 10 ngEE2/L in the muscle in both immature and mature ERE-TG fish. These data demonstrate that muscle is as susceptible as liver and gonad to EE2 and ERE-TG fish (both immature and mature fish) would appear to be a useful system for both detecting target sites for oestrogen chemicals in these life stages fish. In summary, the work undertaken in this thesis has developed transiently and stably transfected zebrafish as a tool for screening oestrogen chemicals to assess for the potential health impacts of oestrogens in the environment, provided novel insights into many tissue target tissues by oestrogen exposure, and has established different patterns of tissue responses for different environmental oestrogens tested suggesting differing functional implications.

Vibration induced by walking pedestrians has motivated research in the civil engineering community for many years. An area within this broad field that has received particular attention is the dynamic interaction that can occur between pedestrians and laterally flexible bridge structures. Perhaps the most notable example occurring on the opening day of London's Millennium Bridge. The enduring interest in this research problem is fuelled by two of its key features; (i) the sensitivity and adaptability of human balance to lateral motion and (ii) the spatial and temporal variation in flow characteristics exhibited by a pedestrian crowd. Both of these features are addressed herein. In this project an experimental campaign was executed with the aim of identifying the interaction mechanism by which pedestrians produce force harmonics, that resonate with the oscillating structure on which they walk. These so-called self-excited forces have been experimentally identified by others but the underlying reason for their existence has remained an open question. In an effort to address this, human balance behaviour while walking on a laterally oscillating treadmill was recorded using 3-dimensional motion capture equipment. Subsequent analysis revealed that human response to sinusoidal base motion is dominated by periodic alteration of foot placement position. This produces amplitude modulation of the lateral component of the ground reaction force and is ultimately responsible for the self-excited force harmonics. It was further revealed that human centre of mass motion while walking on an oscillating structure is predominantly passive. The passive inverted pendulum model is thus an excellent model of pedestrian frontal plane balance. The second facet of this work is concerned with developing a crowd-structure interaction model that builds upon the current state of the art. The model presented utilises the understanding of human-structure interaction identified above and employs an agent-based modelling approach. Thus, the resulting 'virtual crowd' is capable of simulating key crowd features, such as inter-subject variability and emergent velocity-density flow behaviour. Using this model, it is shown that the experimentally identified human-structure interaction mechanism can lead to large amplitude lateral deck oscillations, consistent with field observations reported in the literature. The model successfully predicts the multi-mode instability of Bristol's Clifton Suspension Bridge in the absence of step frequency tuning among the crowd. This provides supporting evidence for the model's validity. The work described above has resulted in a clearer understanding of the feedback between pedestrian balance behaviour and bridge response. Furthermore, the modelling techniques developed have potential for application in the wider study of crowd-induced vibration of dynamically susceptible structures.

This thesis focuses on the simulation of flow around bluff bodies and bridge deck sections, in which unsteady nature and vortex shedding of flow are commonly found, using computational fluid dynamics (CFD). Various turbulence models have been tested to develop understanding and proper modelling techniques for the flow around such bodies. Throughout the thesis, the turbulence models employed, mainly large eddy simulation (LES) and detached eddy simulation (DES), have been validated through comparative study with experimental work. The major part of the work discusses flow around bluff bodies ranging from a simple circular cylinder, a square cylinder to rectangular sections with various aspect ratios (1:2 to 1:8). The research section concentrates on modelling flow characteristics around bluff bodies to investigate the impact of fluid flow on them. This aids in the understanding of a more complex flow around bridge deck sections. The thesis combines investigation and discussion of the vortex shedding nature on the flow around bluff bodies, in which the simulations are done using advanced modelling techniques on high performance computing system. Work also includes a sectional wind tunnel test of the bridge deck section for the comparative study with the numerical solution. Finally, the conclusions outline the achievements and findings of the work done in this thesis and give recommendations for further research on the topic.

Bridges are an important part of the infrastructure of both road and rail networks. As bridge stocks age it is becoming increasing important to monitor their health and predict their lifespan. Current health assessment methods of visual inspection have many drawbacks and so non-destructive evaluation methods such as GPS are becoming more important. This study focuses on the use of single frequency GPS for bridge deformation monitoring. Previous studies have focussed on the use of more expensive dual frequency receivers. This thesis has resulted in the development of single frequency processing software that has enabled these receivers to be used in bridge deformation situations. Improvements in integer ambiguity resolution methods mean it is now possible to be resolve ambiguities instantly for small bridges and greatly reduces ambiguity time for long bridges. The development of this software is outlined along with results from bridge trials. The thesis further looks at extensions to the use of single frequency GPS by outlining experiments conducted with Garmin handheld receivers and also with JNS 100 receivers measuring at 50 Hz. The potential to use Garmin receivers in monitoring applications is demonstrated. The use of 50 Hz data enables the identification of higher frequency bridge dynamics than has ever been possible before. The final investigation looks at using pseudolites to augment the current GPS constellation specifically for bridge monitoring applications. The introduction of pseudolites led to improvements in all three coordinate directions, with the most improvement being seen in the vertical direction.