No description available.

This dissertation examines the collapse of masonry structures in response to large support displacements and horizontal ground accelerations. There are two main classes of masonry structure: arches that thrust, and supporting elements, such as walls and buttresses, which resist the thrust. This dissertation analyses the safety of arches and buttresses and identifies the resulting collapse mechanisms due to support displacements or horizontal accelerations. In particular, this research investigates the stability of a masonry arch supported on buttresses and the conditions necessary for collapse to occur. Engineers are frequently asked to determine the safety of masonry structures that have been severely distorted over the years, often due to subsidence or other long-term movements in the foundations, and this dissertation provides guidance in the assessment of such structures. The resistance of masonry buttresses to high-level horizontal loads is examined. In the case of failure due to overturning, a fracture will develop in the masonry, significantly reducing the resistance of the buttress. The capacity is further reduced by outward leaning of the buttresses, a common source of distress for masonry structures due to movements in the supporting foundations. Based on these considerations, new measures of safety are proposed for buttresses under horizontal loading. Outward leaning of the buttresses increases the span of the arch or vault. Spreading supports will cause large deformations in the arch, which increase the horizontal thrust of the arch and may lead to collapse. In addition, lateral ground accelerations can cause the collapse of arches. The influence of seismic action can be approximated to first order by equivalent static analysis to determine the initial collapse mechanism. These problems are analysed for circular masonry arches, and the collapse conditions are identified for various geometries. The findings are combined to investigate the stability of the masonry arch supported on buttresses. The safety of the system is examined by studying the influence of imposed displacements. As the buttresses lean, the thrust of the vault increases and the resistance of the buttress decreases. The collapse mechanisms are identified for both the static case of leaning buttresses and the dynamic case of horizontal acceleration. This analysis illustrates that the arch will collapse and the buttresses will remain standing in most cases. Based on these considerations, new methods are proposed for assessing the safety of masonry structures and determining the influence of future movements on the stability of existing masonry structures.

The deterioration of the underground infrastructure of the major cities around the world, due to ageing, has become a topic of great concern among engineers. Visual inspection, as part of the routine maintenance procedures, is a common practice used in the condition assessment of infrastructure to ensure its safety and serviceability. This practice, however, is labour-intensive, costly and inaccurate and, therefore, a new system based on computer vision technology is presented in this thesis, aiming to tackle these inadequacies. This thesis proposes a novel mosaicing system for inspection reporting, which can create an almost distortion-free mosaic of tunnels, thus allowing a large area of tunnels to be visualised. The system relies on Structure from Motion (SFM), which enables the system to cope with images with a general camera motion, in contrast to standard mosaicing software that can cope only with a strict camera motion. The system involves the automatic robust estimation of a 3D cylindrical surface using a Support Vector Machine to classify 3D points to improve the accuracy of the estimation. It is shown that some curvatures are observed in the mosaics when an inaccurate surface is used for mosaicing, while the mosaics from a surface estimated using the proposed method are almost distortion-free. New feature matching algorithms aiming to improve the performance of SFM systems are proposed. These algorithms apply a spatial consistency constraint to match features with a similar topography, in contrast to other matching algorithms that rely on matching based on the similar appearance of local image patches. The Shape Context and Random Forest algorithms are combined in the proposed algorithm, revealing promising results. The final contribution is a new change detection system for monitoring cracks in multi-temporal images. The system can cope with images with a general camera motion achieved by geometrical registration using SFM, unlike other systems that assume fixed or controlled cameras. The system performs photometric normalisation to cope with illumination variation in the images, and also a motion-invariant change detection algorithm is applied to handle deformable objects. It is shown that the results from the proposed change detection system are still impractical for use with tunnel images from a real environment, and further study is required.

'Compliant' structures, i. e., structures that undergo large deformations as part of their normal behaviour, can perform the function of a complex mechanism with just a single, or very few, components. When multistability is introduced into compliant structures, an even greater simplification can be made, with actuators and/ or locking mechanisms becoming redundant. Corrugated shells are commonly encountered at all scales of engineering, providing shell structures of a dramatically increased stiffness at little extra cost or weight. What is historically less understood is the compliant behaviour of corrugated shells. The topic of this thesis, therefore,' is the development and analysis of new categories of structure incorporating corrugations, utilising their compliancy to achieve morphing behaviours that are not otherwise possible. Three distinct categories of shell are studied: (i) 'flat' corrugated sheets, which are multistable under the action of internal stresses, 'snapping' between their flat state and a cylindrically coiled state: these shells are also capable of developing 'twisted' stable states. An algebraic model based on internal strain energy determines the conditions for the various modes of multistability for uniform changes in curvature throughout the shell, and a plastic flow model describes the formation of the internal stresses; (ii) 'curved' corrugated sheets, 'which can morph between shapes of differing Gaussian curvature without plastic deformation. Again, a simplified algebraic model describes their behaviour, as does a numerical model. These models consider the strong coupling that occurs between bending and stretching in corrugated shells; and (iii) 'doubly-corrugated ' sheets, similar to an eggbox in concept, which , again, can morph between shapes of different Gaussian curvature, and also exhibit synclastic bending behaviour. Some of the analyses performed on the curved corrugated sheets are also applied to these shells. The qualitative behaviour of the analytical models matches, in every detail considered, the behaviour observed in prototypes. Natural-mode analyses on the category (ii) and (iii) shells demonstrate that the interesting behaviour occurs at relatively low stiffnesses, implying that t his behaviour is potentially useful. Quantitatively, however, the analyses for categories (i) and (iii) above do not prove simple to verify. Physical tests compare the internal stresses of the category (i) shells to those predicted by the plastic flow analysis: the predicted stresses exceed those measured by, typically, 50 %, but it is not established whether the discrepancy is due to the simplifications in the model, inaccuracies in the crude test method or a flmv in om understanding. On its prediction of the curvatures created, the model is more successful. A test is more easily devised for the category (ii) shells, and measurements of the shape change are within 4 % of both the finite-element simulations and the simplified algebraic models over 90 % of the test range. In measuring forces, to test the constitutive relations produced; the accuracy is lower, largely due to the difference between our material model and the real properties of the polymer used: there is strong agreement between the finite element model and the algebraic model. In conclusion, this thesis is successful in generating new varieties of structure, which have a a wide potential for application. A broad range of designs and analyses are presented, describing the behaviour of these structures well enough that our understanding of them seems justified. Nonetheless, this work merely scratches the surface of what may be achieved in this field, demonstrating some of the potential of such shells and leaving much to be done in their further evaluation and development.

Reinforced concrete (RC) structures are usually subjected to various types of loadings, such as permanent, sustained and transient during their lifetime. Reinforced concrete slabs are one of the most fundamental structural elements in buildings and bridges, which might be exposed to unfavourable conditions such as, impaired quality control, lack of maintenance, adverse environmental effects, and inadequate initial design. Therefore, the resistant capacity of the affected elements would dramatically be reduced which most likely leads to the partial or whole collapse of the structure. Non-destructive testing (NDT) techniques can be used to inspect for defects without further damaging the tested component. Significant research and development have been conducted on the performance of vibration characteristics to identify damage in different types of structures. The vibrations based damage detection methods, particularly modal based methods, are found to be promising in evaluating the health condition of a structure in terms of detection, localisation, classification and quantification of the potential damage in the structure. Damage in composites and the non-homogeneous material is tricky to assess from a surface inspection alone. Although the development of NDTs, especially experimental modal analysis (EMA), has been pushed forward by the aerospace industry where composites materials are employed in many safety critical applications, EMA is not widely employed to diagnose all types of RC structural members. Damage detection in reinforced concrete square slabs is the primary aim of this study. This is achieved experimentally using experimental modal analysis (EMA) and numerically using finite element method (FEM). Artificial neural network (ANN) is also used in this study to classify the void sizes. A whole testing procedure of EMA on freely supported slab was established in this research. It is based on impact hammer technique, as a relevant excitation source for field measurements. After the quality of the measurements had been ensured, the experimental data was collected from four pairs laboratory-scale reinforced concrete slabs modelled with various ranges of parameters. After collecting data, Matlab software was employed to obtain modal parameters, such as natural frequencies, mode shapes and modal damping ratios from two RC square slabs. EMA and FEM studies were undertaken to assess and improve modelling technique for capturing the aim. FEM was used to model the RC slabs using commercial ANSYS software. To balance model simplicity of RC slabs with the ability to reliably predict their dynamic response, both predicted and measured dynamic results were compared to ensure that the analytical model represents the experimental results with reasonable accuracy. ANSYS software was also employed to numerically extract the natural frequencies of the slab. Then, using Matlab software, the extracted natural frequencies were fed as the input to the ANN to classify the void sizes in the slab. The dynamic properties of the slab were investigated for each of four pairs to evaluate modal parameters (natural frequencies, damping ratio and mode shapes) sensitivity to slab's dimensions, degree of damage owing to incremental loading and induced void. The performance of EMA based on impact hammer technique was credibly tested and verified on measurements, which were collected from eight slabs with various parameters. EMA efficiency was conclusively proved on data from modal parameters sensitivity to slab's dimensions, incremental loading and induced void. The results indicated that using a bigger reinforced concrete slabs (1200 x 1200 mm2) could potentially have further reduced the discrepancy between theoretical (analytical and numerical) and experimental natural frequencies than smaller slabs (600 x 600 mm2). In general, for the specimens tested slabs, natural frequencies were more sensitive to the damage introduced than the damping ratio because the damping did not consistently increase or decrease as damage increased. The changes in mode shapes tended to increase with increasing damage level. Even small damage induced poised changes to the mode shapes, but it may not be obvious visually. Utilising sophisticated methods for damage identification, which are vital steps in higher level of damage detection in structures, is one of the major contributions to the knowledge. The proposed Modal Assurance Criterion (MAC) and Coordinate Modal Assurance Criterion (COMAC) techniques as advanced statistical classification model were employed in this study. From the vibration mode shapes induced void location can be identified via MAC and COMAC techniques when both intact and damaged data were compared. MAC provided a clear change in the mode shape while the COMAC provided the change in specific a location whereby the location of damage was identified. The outcomes of this two techniques can show the realistic location of the void. Beside the aforementioned contributions in this research, the feasibility of a Feed-Forward Back Propagation Neural Network (FFBPNN) was investigated using ten natural frequencies as input and the void sizes as output. Excellent results were obtained for damage identification of four void sizes, showing that the proposed method was successfully developed for damage detection of slabs. The results proved that the precision of the models was reduced when dealing with small size void. The large size void was detected more accurately than small size void as expected. This is because the natural frequencies of the small void of different location attributed together. Therefore, natural frequencies alone were not considerably good enough to make good identifications for small size void. Moreover, the natural frequencies set of three untrained void specifications were used as FFBPNN inputs to test the performance of the neural networks. The obtained results show that the proposed network can predict the void specifications of the unseen data with high accuracy. Overall, the methodology followed in this work for damage detection in reinforced concrete square slabs is novel when compared to the breadth and depth of all other previous works carried out in the field of reinforced concrete structures.

No description available.

Climate change poses real threats to the sustainability of slopes, particularly in the tropical region of the world. Its effects have caused a greater occurrence of extreme climate events that are reflected in a greater occurrence of slope failure incidents for this region. The hydro-mechanical characteristics of soils linked with climate variation are factors that can explain deterioration in slope stability. Therefore, the ability to analyse the hydro-mechanical behaviour properly is worthy of investigation and this can be done by the use of experimental investigation and numerical modelling using both saturated and unsaturated soil properties. In this thesis, the description of the important effects of climate impacts on slope stability has been made for a failed tropical residual soil slope located in Precinct 9, Putrajaya, Malaysia. Part of the work involved soil sampling for the acquisition of undisturbed soil samples from the slope. Series of advanced saturated and unsaturated laboratory testing for both hydrological and mechanical properties have also been implemented and were used in transient, unsaturated numerical modelling of slope stability analysis (using Plaxis 2D). The results demonstrate that within a slope the mobilised shear strength drops quickly during a rainfall event (due to rainfall infiltration) but recovers much more slowly during drying. This shows how a series of regular rain storms with short periods of drying in between can cause a ratcheting effect, with rapid loss of strength during each period of rain that is not recovered during the intermediate drying periods. In addition, the results also show that the adoption of critical state soil parameters is more suitable to match the observed failure. The failure was due to a very extreme amount of rainwater infiltration in the two days before the incident, including the largest daily rainfall in 2007 of 140mm.

The multi-disciplinary nature of closing the loop (CtL) between 4D seismic and reservoir engineering data requires integrated workflows to make sense of these different measurements. According to the published literatures, this integration is subject to significant inconsistency and uncertainty. To resolve this, an engineering consistent (EC) concept is proposed that favours an orderly workflow to modelling and inverting the 4D seismic response. Establishing such consistency facilitates a quantitative comparison between the reservoir model and the acquired 4D seismic data observation. With respect to the sim2seis workflow developed by Amini (2014), a corresponding inverse solution is proposed. The inversion, called seis2sim, utilises the model prediction as a priori information, searching for EC seismic answers in the joint domain between reservoir engineering and geophysics. Driven by a Bayesian algorithm, the inversion delivers more stable and certain elastic parameters upon application of the EC constraints. The seis2sim approach is firstly tested with a synthetic example derived from a real dataset before being applied to the Heidrun and Girassol field datasets. The two real data examples are distinctive from each other in terms of seismic quality, geological nature and production activities. After extracting the 3D and 4D impedance from the seismic data, CtL workflows are designed to update various aspects of the reservoir model according to the comparison between sim2seis and seis2sim. The discrepancy revealed by this cross-domain comparison is informative for robust updating of the reservoir model in terms reservoir geometry, volumetrics and connectivity. After applying tailored CtL workflows to the Heidrun and Girassol datasets, the statistical istributions of petrophysical parameters, such as porosity and NTG, as well as intra- and inter-connectivity for reservoir compartments are revised accordingly. Consequently, the 3D and 4D seismic responses of the reservoir models are assimilated with the observations, while the production match to the historical data is also improved . Overall, the proposed seis2sim and CtL workflows show a progression in the quantitative updating of the reservoir models using time-lapse seismic data.

The use of stone columns as a means of ground improvement has been in use for over 40 years in the United Kingdom and Europe. Their primary purpose is to reduce settlement, reduce consolidation time and increase the bearing capacity of soils. Currently the technique is applied to a variety of soil types, cohesive and granular. Soft cohesive soils have shown a tendency towards higher settlements due to the inability of the soil to restrain the lateral movement or bulging of stone columns. Current analytical design methods are based upon the unit concept which considers a stone column to be part of an infinite array of columns. Such methods have proved useful when designing large arrays such as those utilised beneath embankments or large rafts. Columns within the group are restrained equally on all sides and held in the same vertical stress conditions. However, at the edge of large (wide) load areas and in smaller foundation configurations columns are not generally restrained on all sides by other columns and must rely on the soil to provide restraint in the outward facing directions. The behaviour of small foundation configurations is more complex due to this lack of restraint with columns subject to deformation at lower stress levels than those in infinite arrays. This dissertation is concerned with the behaviour of stone columns and proposed composite stone columns installed in soft clay. This research compares the behaviour of small foundations supported by stone columns to behaviour within an infinite array of columns. Specifically the settlement and deformation behaviour of stone columns are considered to identify the main deformation mechanisms and to examine the effect of key design parameters and soft cohesive soils on column performance. A new form of composite stone column was then examined numerically to assess the potential for enhanced column behaviour and settlement reduction. PLAXIS 3D Foundation is utilised with column behaviour represented by the Mohr-Coulomb Perfect Plasticity model and the Hardening Soil model adopted to model soil behaviour. The soft soil profile adopted in this research is the well characterised Bothkennar soft clay site which was formerly the UK geotechnical test bed. The influence of key stone column design parameters, area ratio, column length, column confinement and arrangement, column stiffness, column strength, installation effects and the effect of stiff crust thickness was examined for a combination of foundation types with 432 numerical sensitivity studies conducted. The results reveal that area ratio and column length have a significant impact on the settlement performance of stone columns. Increasing the area ratio was found to reduce the restraint provided by neighbouring columns leading to increased settlement. Increasing column length was found to reduce settlement. When columns were modelled with low area ratios increasing column length had a greater effect on settlement reduction than at higher ratios. The design parameters of area ratio and column length are established as the controlling parameters for the mode of deformation. The mode of deformation was examined utilising settlement inferred deformation ratios (compression and punching) with comparison to total shear strain plots and stress states in the column. Two primary modes of deformation, bulging and punching (including sub-type termed 'block failure') were inferred. Punching failure was inferred for short columns by high punching ratios and low compression ratios with a concentration of shear strain observed at the base of the floating columns. A sub-type of punching, block failure, was inferred from low compression and low punching ratios for closely spaced columns with low area ratios in which the columns act as one unit punching into the underlying soil. Bulging failure was inferred by low punching ratios and high compression ratios coupled with a concentration of shear strain in upper region of the columns. The magnitude of bulging was found to be at its most severe for high area ratios. Bulging as a mode of failure occurred for column length to diameter ratios greater than 4 and area ratios greater than 8. Bulging was found to occur at the weakest of the soil profile which coincides with the top of the lower Carse clay. Consideration was given to a method of reducing the potential for lateral column deformation or bulging by the use of a novel composite column. The deformational characteristics of a stone column were identified for a composite of granular and the experimental Protomix materials. Laboratory testing was carried out to gain an understanding of the cohesive, stiffness and unconfined compressive strength properties of the composite before simulation studies were performed on key design parameters such as area ratio, column length, column confinement and arrangement for a combination of foundation types with 108 numerical analysis sensitivities conducted. The inclusion of a cohesive 'binder' material in the bulging zone was found to reduce settlement for all foundation configurations. Similarly to stone columns area ratio and column length were found to be the design parameters which influenced the results most. The composite stone columns (CSC) offered higher settlement reduction than traditional stone columns (SC). It was discovered that CSC with an area ratio of 8 were able to achieve the same settlement improvement factor as those with a ratio of 3.5 which suggests the columns could offer the same settlement control but with large column spacing's making their use more economical. The settlement inferred deformation ratios (compression and punching) were studied while monitoring the total shear strain field cross sections to examine if composite stone columns would behave similarly to a stone column. It was noted that the same modes of deformation of punching (including block failure) and bulging failure were observed. The increased stiffness in the bulging zone saw the transfer of bulging type effects to a depth below the composite treated zone. It was only observed for high area ratios. The improved settlement behaviour of CSC compared to SC is due to the treatment of the bulging zone by CSC and improved column restraint at depth provided by the soil. Punching failure was found to have a higher magnitude and occur to a deeper depth of 3.6 m compared to SC depth of 2.4 m due to the addition of the composite material. The modes of deformation observed for SC were also observed for the new novel CSC columns. This suggests that the same type of foundations can be used and so avoid the need for reinforcement of the foundations as used with piled foundations.

Building works include construction and demolition activities, which are common in cities across the world. Building-related activities contribute a considerable amount of the construction and demolition waste material worldwide. These activities have the potential to produce particulate matter (PM), including PM10 (≤10 μm), PM2.5 (≤2.5 μm) and PM1 (≤1 μm), and airborne ultrafine particles (≤0.1 μm). Recent studies have indicated that the rate of building works undertaken each year is growing exponentially, to meet new urban design guidelines and respond to demand from the adoption of new building technologies, which highlights the importance of measuring the amounts of particle emissions from these sources. The principles of sustainable urban development are well established, but the extent of pollution due to construction and demolition activities is still unknown. Through laboratory and field studies, this thesis aims to comprehensively investigate the release of coarse (referred to as PM2.5–10 fraction), fine (PM2.5) and ultrafine particles from various building works, assess their physicochemical properties, and estimate the associated occupational exposure risk from them to on-site workers and individuals in the close vicinity. Experiments for this thesis were carried out to measure PM and airborne ultrafine particles in the size range of (0.005–10 µm) using a fast response differential mobility spectrometer (DMS50), a tapered element oscillating micro balance (TEOM 1400), a GRIMM particle spectrometer (1.107 E) and OSIRIS (2315). Measurements were made in various locations: a controlled laboratory environment (i.e. concrete mixing, drilling, cutting), indoor field sites (i.e. building refurbishment) and at outdoor field sites (i.e. construction and demolition). Moreover, dust samples were collected simultaneously for physiochemical analyses (e.g. SEM, EDS, XPS and IBA). Several important findings were then extrapolated during the analysis. These findings indicated that ultrafine particles dominated (74-97%) the total particle number concentrations (PNCs) while the coarse particles (PM2.5-10) contributed to the majority of the total particle mass concentrations (PMCs), during the laboratory, indoor and outdoor field experiments. The highest proportion of PNCs and PMCs was found during the concrete cutting, drilling and wall chasing activities. In addition, the highest proportion of PMCs was observed in the excavator cabin during a building demolition at an outdoor field measurement site. Moreover, combining the results of SEM, EDS, XPS and IBA analysis suggested the dominance of elements such as Si, Al and S in the collected samples. The data were also used to assess the horizontal decay of the PMC through a modified box model to determine the emission factors and the occupational exposure to on-site workers and nearby individuals. The results confirmed that building-related works produce significant levels of coarse, fine and ultrafine particles, and that there is a need to limit particle emissions and reduce the occupational exposure of individuals by enforcing effective engineering controls. These findings could also be useful for the building industry to develop mitigation strategies to limit exposure to particulate matter during building works, particularly for ultrafine particles, which are currently non-existent.