Rozprawy doktorskie na temat „COLLAPSE ASSESSMENT”

The collapse of buildings over the last century as a result of abnormal loads has renewed interest in the field of structural engineering. Key events such as the disproportionate collapse of the Ronan Point building in London, the collapse of the Alfred Murray Building and the World Trade Centre are structural failures that have triggered more research into progressive collapse. Consequently, new design guidelines around the globe with a prescriptive recommendation for improving structural integrity based on tying force provision have been developed. However, in existing design guidelines and codes throughout the world, there is a lack of a codified modelling technique for progressive collapse. As a result of this limitation, researchers adopt different methods. Generally, during the progressive collapse, structural members experiencing significant displacements and rotations, while the beam-column connections are subjected to large tensile forces not envisaged at the conventional design phase. Hence, this study presents an assessment of the effect of column removal time, the modelling techniques and the susceptibility of simple connections designed to Eurocode 3 Part: 1-8 to progressive collapse. A computationally efficient approach and column removal time for progressive collapse assessment are proposed. The findings show that a braced framed system is likely to exhibit at least 35% progressive collapse when compared with a moment resisting frame system using the joint displacement and rotation criteria. Furthermore, the research shows that the UK tie provision in EN1991-1-7 underestimates the magnitude of the catenary force developed under the progressive collapse scenario. Consequently, the connection is disposed to progressive collapse with the shear force in the column and catenary action in the beam as the critical internal forces. Based on this assessment, five times the tensile force specified in EC3 for tensile force connection design checks is recommended. Shear force in the column and catenary force action in the beam are the internal governing forces that determine the maximum dynamic amplification factor of a simple connection. The work provides evidence that the tie beam-column web connection at the corner column is more critical under progressive collapse scenario as compared with the primary beam. Column web failure in yielding is attributed to the large catenary force developed in the tie beam connected to the web of the column.

The events of 11 September 2001 have instigated a comprehensive debate among the structural engineering community regarding the performance of tall buildings under extreme loading conditions such as blast, impact or fire. The main issues that have been identified include the dynamic robustness of such buildings, the parameters that could possibly initiate progressive collapse following the extreme event, and the design guidance that needs to be introduced in order for buildings to survive such events and assure life safety of their occupants. Since the structural components of buildings subject to extreme loading events are likely to undergo large inelastic deformations, which can induce excessive ductility demands in the joint regions of the members involved, the behaviour and modelling of joints is discussed in detail. With respect to design recommendations, this thesis proposes a multi-level framework for progressive collapse assessment of building structures subject to sudden column loss, which is the design scenario adopted by most recent guidelines to assess the potential of multi-storey buildings for progressive collapse. The proposed framework offers a rational and practical means for assessing structural robustness at various levels of structural idealisation, it accommodates both simplified and detailed models of the nonlinear structural response, and importantly it moves the debate on structural robustness towards the quantifiable. Application of the new approach is demonstrated with reference to steel-framed composite buildings with partial-strength joints. Furthermore, a methodology is developed, based on the proposed assessment framework for sudden column loss, to consider the impact of floor failure on a lower floor, in order to establish whether this would in fact trigger progressive collapse. Application of this methodology is also illustrated by means of a case study, where consideration is given to a floor grillage system subject to impact of the floor above, and the ability of the impacted floor members to sustain the dynamically induced loads associated with various impact scenarios is thoroughly examined. From the presented application studies, important conclusions are drawn relating to the inherent robustness of steel-framed structures, the factors influencing this robustness, and the adequacy of current regulations for the avoidance of progressive collapse.

Restrições econômicas e ecológicas têm limitado o investimento em novas usinas e linhas de transmissão de energia elétrica. Com os sistemas de potência trabalhando bastante carregados, o risco da ocorrência da instabilidade de tensão se acentua. Neste trabalho estabeleceram-se as características operacionais do fenômeno do colapso de tensão, e sua similaridade e diferença em relação ao problema da estabilidade angular. Forma desenvolvidos métodos para avaliar um ponto de operação do sistema quanto à proximidade da ocorrência do fenômeno. Os resultados foram comparados. Finalmente, foi abordado o problema da prevenção do colapso
Investiments on new generators and transmission lines for electrical power systems have been limited due to economical and environmental constraints. This dissertation established the operational characteristics of the voltage collapse phenomenon, as well as pointed out similarities and differences in relation to the angular stability problem. Voltage collapse assessment methods were developed and results compared. Finallu, the collapse prevention problem was mentioned.

This thesis investigates the progressive collapse behaviour of lightweight ship hull girders including the effects of compartment level buckling modes. An extension to the progressive collapse methodology is proposed, which has capabilities to predict the compartment strength of a lightweight aluminium midship section. Nonlinear finite element analysis is used to validate both the progressive collapse methodology and the analytical approach proposed for determining the buckling capacity of orthogonally stiffened substructures within the hill girder compartment. The research has been undertaken due to the continued growth in the size of large lightweight craft in both commercial and naval vessels, combined with increasing operability requirements for these vessels. The development of large and lightweight marine structures, predominantly built from aluminium alloy, has raised important issues regarding the response of the hull girder under primary hull girder bending.

Earthquakes represent a serious threat to the safety of masonry structures, with failure of these constructions under the influence of seismic action generally occurring via specific, well-documented collapse mechanisms. Analysis and assessment of these collapse mechanisms remains a challenge - while most analysis tools are time-consuming and computationally expensive, typical assessment methods are too simplified and often tend to underestimate the dynamic resistance of the structures. This dissertation aims to bridge the gap between the two through the development of a computational tool for the seismic collapse assessment of masonry structures, which uses rocking dynamics to accurately capture large displacement response, without compromising on computational efficiency. The tool could be used for rapid evaluation of critical mechanisms in a structure in order to prioritise retrofit solutions, as well as for code-based seismic assessment. The framework of the tool is first presented, wherein the rocking equations of motion are derived for a range of different collapse mechanisms, for any user-defined structural geometry, using as a starting point a geometric model of the structure in Rhino (a 3D CAD software). These equations of motion are then exported for solution to MATLAB. As a number of collapse mechanisms take place above ground level, a methodology to account for ground motion amplification effects is also proposed, while in the case of comparison of multiple different mechanisms, an algorithm to automatically detect critical mechanisms is presented. These developments make it possible to rapidly conduct a seismic analysis of structures with complicated three-dimensional geometries. However, the rocking equations of motion utilised thus far assume that the interfaces between the masonry macro-elements are rigid, which is not the case in reality. Thus, a flexible interface model is introduced, where the interfaces are characterised by a finite stiffness and compressive strength. This modelling strategy results in an inward shift of the rocking rotation points, and expressions are derived for these shifting rotation points for different interface geometries. The rocking equations of motion are also re-derived to account for the influence of the continuously moving hinges. However, the new equations tend to be highly non-linear - especially in the case of more complex collapse mechanisms. Thus to reduce computational burden, the semi-flexible interface model is proposed, which accounts for the shifting hinges in a more simplified manner than its fully-flexible counterpart. These new analytical models enable more accurate prediction of the seismic response of real-world structures, where interface flexibility tends to have a significant influence on dynamic response, while material damage in the form of crushing of the masonry also reduces dynamic resistance. The ability of the tool to be used for both seismic analysis and assessment is finally demonstrated by using it to perform a rocking dynamics-based analysis as well as a code-based seismic assessment of the walls of a historic earthen structure.

The Buller Coalfield comprises the northern end of the Paparoa Trough, an elongate basin that began to subside in the mid Cretaceous. Subsidence occurred in response to mid Cretaceous extension, leading to crustal thinning, and culminating in opening of the Tasman Sea. The area underwent asymmetric subsidence between the mid-late Eocene and the late Oligocene, controlled by normal faulting, inferred to occupy the same position as the present day Kongahu Fault Zone. Inversion of the Paparoa Trough commenced in the late Oligocene, by reactivation of normal faults as reverse/thrust faults through a regional change from extension to shortening and establishment of the Alpine Fault as a new plate boundary. Positive inversion progressed through a number of phases over the last 25Ma producing the present day Buller Coalfield. Four sets of Quaternary coastal marine terraces are recognised within the Westport region. Preservation and tilting of this terrace sequence is indicative of progressive regional uplift continuing through to the present day. Large scale gravitational collapse structures (forming the Kongahu Fault Zone Failure Complex, with a surface area of approximately 18km² have formed over several hundred thousand years, along the escarpment separating Tertiary units on Denniston Plateau from Quaternary deposits along the coastal plain. Landslide materials of the Kongahu Fault Zone failure are very complex and have been subdivided into four zones based on slide geology and surface morphology. Six separate deformation phases have been identified based on interpretations of geomorphic evolution of the failure complex. Initial failure is inferred to have taken place along unfavourably oriented rockmass defects, such as bedding planes, joint sets and faults, with destabilisation initiated through head loading (caused by tectonic uplift) and removal of toe support through erosion of Late Tertiary units. Preservation of Caledonian Formation marine terraces and associated deposits, on the landslide complex, places this event beyond 334 000 years BP. Later phases of reactivation of the landslide complex are related to interglacial high stands in sea-level and ongoing fluviatile erosion, removing toe area support. The initial rupture surface is inferred to have propagated along bedding planes within the Brunner Coal Measures, but as the failure complex evolved the rupture surface propagated into sheared granitic basement, forming large-scale, deep-seated III collapse. Preservation of coastal marine terraces in the toe area of the main failure complex, fonned during the last interglacial period are indicative of stability of the main failure complex since approximately 58-72 000 years BP. However, interpretation of geomorphic features upon the coastal plain indicate extremely slow deep-seated activity within the central "Mt Rochfort Failure". A seismic hazard assessment of the main Kongahu Fault Zone failure complex indicates that it is inherently stable and unlikely to undergo large scale reactivation through high intensity ground shaking. Seismically triggered local rock falls , rock avalanches and rapid soil flows form the dominant hazard associated with earthquake triggered failure. Only one section of the failure complex, the "Mt Rochfort failure", is considered to still be active although inferred to be failing as extremely slow, deep creep. Localised recent failures are primarily related to antecedent pore water conditions and triggered by intense or prolonged rainfall and seismic events. These create a low level hazard due to lack of human interaction in areas where the failures occur. Reactivation of debris within fluvial channels leading to avulsion onto fan surfaces along the coastal plain forms the dominant hazard. Lake Rochfort is a landslide formed lake (approximately 320 000m ³), 460m above the coastal plain, located within the active Mt Rochfort Failure. By comparison with the (1981) Ram Creek Dam burst, it has been concluded that catastrophic failure of Lake Rochfort would destroy property and services with the potential for causing serious injury and loss of life on the coastal plain.

Vulnerability of buildings to disproportionate (or progressive) collapse has become an increasingly important performance issue following the collapses of the Alfred P. Murrah Federal Building in Oklahoma City in 1995 and the World Trade Center in 2001. Although considerable research has been conducted on this topic, there are still numerous unresolved research issues. This dissertation is aimed at developing structural models and analysis procedures for robustness assessment of steel building structures typical of construction practices in the United States, and assessing the performance of these typical structures. Beam-column connections are usually the most vulnerable elements in steel buildings structures suffering local damage. Models of three typical frame connections for use in robustness assessment have been developed with different techniques, depending on the experimental data available to support such models. A probabilistic model of a pre-Northridge moment-resisting connection was developed through finite element simulations, in which the uncertainties in the initial flaw size, beam yield strength and fracture toughness of the weld were considered. A macro-model for a bolted T-stub connections was developed by considering the behavior of each connection element individually (i.e. T-stub, shear tab and panel zone) and assembling the elements to form a complete connection model, which was subsequently calibrated to experimental data. For modeling riveted connections in older steel buildings that might be candidates for rehabilitation, a new method was proposed to take advantage of available experimental data from tests of earthquake-resistant connections and to take into account the effects of the unequal compressive and tensile stiffnesses of top and bottom parts in a connection and catenary action. These connection models were integrated into nonlinear finite element models of structural systems to allow the effect of catenary and other large-deformation action on the behavior of the frames and their connections following initial local structural damage to be assessed. The performance of pre-Northridge moment-resisting frames was assessed with both mean-centered deterministic and probabilistic assessment procedures; the significance of uncertainties in collapse assessment was examined by comparing the results from both procedures. A deterministic assessment of frames with full and partial-strength bolted T-stub connections was conducted considering three typical beam spans in both directions. The vulnerability of an older steel building with riveted connections was also analyzed deterministically. The contributions from unreinforced masonry infill panels and reinforced concrete slabs on the behavior of the building were investigated. To meet the need for a relatively simple procedure for preliminary vulnerability assessment, an energy-based nonlinear static pushdown analysis procedure was developed. This procedure provides an alternative method of static analysis of disproportionate collapse vulnerability that can be used as an assessment tool for regular building frames subjected to local damage. Through modal analysis, dominant vibration modes of a damaged frame were first identified. The structure was divided into two parts, each of which had different vibration characteristics and was modeled by a single degree-of-freedom (SDOF) system separately. The predictions were found to be sufficiently close to the results of a nonlinear dynamic time history analysis (NTHA) that the method would be useful for collapse-resistant design of buildings with regular steel framing systems.

Existing reinforced concrete buildings lacking details for ductile response during earthquake shaking represent prevalent construction type in high seismic zones around the world. Seismic rehabilitation of these existing buildings plays an important role in reducing urban seismic risk; however, with the massive inventory of existing concrete buildings and high costs of seismic rehabilitation, it is necessary to start by identifying and retrofitting those buildings which are most vulnerable to collapse. The collapse of most non-ductile concrete buildings will be controlled by the loss of support for gravity loads prior to the development of a side-sway collapse mechanism. “Gravity load collapse” may be precipitated by axial-load failure of columns, punching-shear failure of slab-column connections, or axial-load failure beam-column joints. In this dissertation, system-level collapse criteria are developed and implemented in a structural analysis platform to allow for a more accurate detection of collapse in these existing moment frames. Detailed models for primary components, which may precipitate gravity-load collapse of the concrete moment frame, are first required to achieve this objective and develop the collapse assessment framework. An analytical model based on mechanics is developed to reliably capture the lateral load–deformation response of a broad range of reinforced concrete columns with limited ductility due to degradation of shear resistance, either before or after flexural yielding. The robust collapse performance assessment could be used for many structural applications. In this dissertation, it is used to identify collapse indicators, design and response parameters that are correlated with “elevated” collapse probability. The collapse assessment framework is also used to identify the relative collapse risk of different rehabilitation techniques. Finally, the framework is used to estimate the impact of collapse criteria on the expected financial losses for existing concrete frame buildings in high seismic zones. This dissertation includes important contributions to (1) modeling techniques for components in existing concrete frames through the development of a mechanical model for existing concrete columns, (2) development of system-level collapse criteria, and (3) application of collapse fragilities in defining collapse indicators, improving loss estimation of existing concrete frames, and differentiating the collapse performances of existing and retrofitted concrete frames.

Accidental events, such as impact loading and explosions, are rare events with a very low probability of occurrence, but their effects often lead to very high human losses and economical consequences. Vulnerability of structures to the effects of local damages and its mitigation are issues widely discussed inside the scientific community. The structural property associated with such a vulnerability is named robustness. Depending on the type of the structural system and on the importance of consequences, specific design strategies can be adopted in order to ensure a robust structural response. Among them, the system redundancy, the joints and members ductility and the alternate load paths are the ones commonly adopted in case of multi-storey framed buildings. The present work focuses on the study of the behaviour of steel-concrete composite structures subjected to a column loss, and proposes a global overview to quantify the robustness of such systems subjected to this hazard scenario. The description of validated finite element models and of a new analytical tool to predict the response of flat concrete slabs subjected to large displacement are reported in this dissertation. Furthermore, important design hints for composite buildings are proposed. The starting point of the research is an experimental campaign conducted at the University of Trento. Two tests on 3D full-scale one storey composite steel-concrete frames, extracted from five storeys frames designed in accordance to the Eurocodes, were performed simulating the central column removal. The role of the beam-to-column connections and of the concrete slab for the force redistribution was investigated. The experimental data have been then taken as reference for the calibration of finite element models that allowed to conduct further numerical analyses on different structural configurations and design scenarios. In particular, it was studied the influence of the location of the removed column on the structural behaviour. The collapse of central, lateral and corner columns were investigated in order to understand the load transfer mechanism, the requirement of joint ductility and the influence of the concrete slab on the development of alternate load paths. Both experimental and numerical results showed that the concrete slab plays a key role on the load transfer mechanism within the structure: it can hence contribute significantly to the robustness of the system preventing progressive collapse. The knowledge of the response of reinforced concrete slabs subjected to large displacements, as in the case of a column loss, allows quantifying the contribution to the resistance of the building to collapse associated with activation of membrane forces. Regarding this aspect, a new analytical simplified method, based on the principle of virtual works, was developed to predict the load-deflection response of simply supported reinforced concrete slabs with planar edge restraints subjected to large displacement. In conclusion, the present work provides a significant contribution to the knowledge of composite steel-concrete structures subjected to extreme loading conditions and open the way to extend results to different structural configurations and loading scenarious.

Accidental events, such as impact loading and explosions, are rare events with a very low probability of occurrence, but their effects often lead to very high human losses and economical consequences. Vulnerability of structures to the effects of local damages and its mitigation are issues widely discussed inside the scientific community. The structural property associated with such a vulnerability is named robustness. Depending on the type of the structural system and on the importance of consequences, specific design strategies can be adopted in order to ensure a robust structural response. Among them, the system redundancy, the joints and members ductility and the alternate load paths are the ones commonly adopted in case of multi-storey framed buildings. The present work focuses on the study of the behaviour of steel-concrete composite structures subjected to a column loss, and proposes a global overview to quantify the robustness of such systems subjected to this hazard scenario. The description of validated finite element models and of a new analytical tool to predict the response of flat concrete slabs subjected to large displacement are reported in this dissertation. Furthermore, important design hints for composite buildings are proposed. The starting point of the research is an experimental campaign conducted at the University of Trento. Two tests on 3D full-scale one storey composite steel-concrete frames, extracted from five storeys frames designed in accordance to the Eurocodes, were performed simulating the central column removal. The role of the beam-to-column connections and of the concrete slab for the force redistribution was investigated. The experimental data have been then taken as reference for the calibration of finite element models that allowed to conduct further numerical analyses on different structural configurations and design scenarios. In particular, it was studied the influence of the location of the removed column on the structural behaviour. The collapse of central, lateral and corner columns were investigated in order to understand the load transfer mechanism, the requirement of joint ductility and the influence of the concrete slab on the development of alternate load paths. Both experimental and numerical results showed that the concrete slab plays a key role on the load transfer mechanism within the structure: it can hence contribute significantly to the robustness of the system preventing progressive collapse. The knowledge of the response of reinforced concrete slabs subjected to large displacements, as in the case of a column loss, allows quantifying the contribution to the resistance of the building to collapse associated with activation of membrane forces. Regarding this aspect, a new analytical simplified method, based on the principle of virtual works, was developed to predict the load-deflection response of simply supported reinforced concrete slabs with planar edge restraints subjected to large displacement. In conclusion, the present work provides a significant contribution to the knowledge of composite steel-concrete structures subjected to extreme loading conditions and open the way to extend results to different structural configurations and loading scenarious.

Performance-Based Earthquake Engineering necessitates the development of simulation models that can predict the nonlinear behavior of structural components as part of a building subjected to seismic loading. For reliable seismic assessment of buildings, these models need to be calibrated with large sets of experimental data. This thesis advances the state-of-knowledge on the collapse assessment of concentrically braced frames (CBFs) designed in seismic regions. The thesis discusses the development of a database that includes extensive information from more than 300 tests of steel braces that have been conducted worldwide over the past 40 years. Statistical information of various properties of steel braces that can be used for quantification of modeling uncertainties is summarized and implications regarding the expected yield properties of various steel types as part of current design provisions are discussed. The steel brace database is utilized to develop drift-based and dual-parameter fragility curves for different damage states of steel braces. These curves can be used as tools for rapid estimation of earthquake damage towards the next generation of performance-based evaluation methods for new and existing buildings. Through extensive calibrations of an inelastic fiber-based steel brace cyclic model, modeling recommendations for the post-buckling behaviour and fracture of steel braces due to low-cycle fatigue are developed for three different brace shapes. The effectiveness of these recommendations is demonstrated through two case studies including concentrically braced frames (CBFs) subjected to earthquake loading. The emphasis is on the accurate assessment of the collapse capacity of concentrically braced frames with the explicit consideration of strength and stiffness deterioration of various structural components that are part of local story mechanisms that develop in CBFs after the steel braces fracture. The influence of modeling classical damping on the collapse capacity of CBFs is also discussed.
Le génie parasismique basé sur la performance des structures nécessite le développement des modèles de simulation qui peuvent estimer le comportement non-linéaire des composantes structurales faisant partie d'un bâtiment sujet ti aux efforts sismiques. Afin d'avoir une évaluation sismique fiable, les modèles doivent être étalonnés avec un grand inventaire de données obtenues expérimentalement. Cette thèse avance l'état des connaissances sur l'évaluation de l'effondrement des contreventements en treillis concentrique conçus dans les régions sismiques. Cette thèse adresse le développement d'une banque de données qui inclut plus de 300 essais effectués autour du monde sur des contreventements en acier depuis plus de 40 ans. Les données statistiques de plusieurs propriétés du contreventement en acier qui peuvent être utilisées pour la quantification des incertitudes de la modélisation sont résumées. Également les implications reliées aux propriétés limi d l'élasticité qui sont attendues selon le type d'acier sont présentées en fonction des règles d'actuelles de conception. La banque de données des contreventements en acier est utilisée afin de développer des drift-based et dual-parameter fragility curves courbes de fragilité à deux paramètres en fonction du déplacement horizontal relatif de l'étage pour différents degrés de dommage. Ces courbes servant à estimer efficacement et rapidement les dommages sismiques, amènt vers la prochaine génération des méthodes d'évaluation de la performance des structures. À travers une vérification approfondie de l'étalonnement du modèle non-linéaire cyclique à fibres du contreventement en acier des recommandations de modélisation du postflambement et de la rupture en fatigue oligocyclique sont développées pour trois différentes types de contreventement. L'efficacité de ces recommandations est démontrée à travers des études de cas incluantes des contreventements concentriques qui reprisent des efforts sismiques. L'accent est mis sur l'évaluation précise de la capacité de l'effondrement des contreventements en treillis concrentriques en prenant en compte explicitement le processus de dégradation de la capacité et de la rigidité des plusieurs composants structuraux qui font partie des mécanismes du dommage local qui s'évoluentdans différents étages d'une structure en contreventements concentriques en acier une fois que le contreventement s'est fracturé. L'effet de la modélisation de l'amortissement de la structure sur la capacité à l'effondrement des contreventements concentriques en acier est également considéré.

The aim of this research is to develop a coupled thermo-mechanical damage model for implementation in finite element software in support of fire-induced collapse assessment of steel structures. The need for properly modelling steel deterioration behaviour remains a challenging task in structural fire engineering because of the complexity inherent in the damage states of steel at large strains and high temperatures. A fully three-dimensional damage-coupled constitutive model is developed based on the hypothesis of effective space elastoplasticity and isotropic damage theory. The coupled damage is simulated by a coupling formulation between a mechanical damage component and a thermal damage component in attempt to capture the coupled damage growth under combined actions of mechanical loading and fire loading. The proposed damage model comprises a limited number of parameters that could be identified at unloading slopes of stress-strain relationships through tensile coupon tests. Alternatively, an inverse analysis type of calibration procedure could be adopted when coupon test data is unavailable. The proposed damage model is successfully implemented in the finite element software ABAQUS and calibrated with a comprehensive range of experimental results and established numerical results. The damage-affected structural response is accurately reproduced under various loading conditions and a wide temperature range, demonstrating that the proposed damage model is a useful tool in giving a realistic representation of steel deterioration behaviour under combined actions of fire and mechanical loads. Three-dimensional FE models of a five-storey and a ten-storey steel-framed office building are developed in ABAQUS and the proposed damage model is adopted in assessing their susceptibility to progressive collapse. Three types of accidental scenarios are investigated : (i) fire only scenario, (ii) post-blast fire scenario, and (iii) fire-triggered explosion scenario. The location of the compartment where triggering loads occur is varied and the most vulnerable location is at the mid-height of both building systems. Estimation of ultimate failure time by incorporating damage model with the suggested damage parameter set has the potential to be utilized as a useful tool in helping designers to determine how much time is realistically available for evacuation before progressive collapse occurs in this type of buildings. Results show that the proposed damage model significantly affects the limit state of steel buildings under fire, and especially under combined actions of blast and fire. Compared to conventional numerical approaches, the consideration of coupled thermo-mechanical damage accumulation results in an 8.25% ∼ 23.47% decrease of collapse resisting time. A key finding from this study is that the alternative load path, which is a crucial factor in deciding the survival of buildings upon local column failure, may be severely compromised due to the coupled thermo-mechanical damage propagation in surrounding columns. Based on the identified collapse mechanisms, effective strategies are suggested to improve the survivability of buildings under blast and fire.

The Simplified Progressive Collapse Method is a quick and well‐established method recommended by International Association of Classification Societies (IACS) for the evaluation of a ship’s ultimate strength due to longitudinal bending. However, in the case which the torsional rigidity of the structure is reduced i.e. containerships, longitudinal bending may not be the dominant reason for failure. Torsion and shear forces may influence the global strength and therefore the effect of combined loading needs to be investigated. The current research aims to understand hull girder failure modes under these combined loads both for intact and damage case scenarios and incorporate torsional loading effect into the existing method. A hull girder which is subjected to longitudinal bending moment and torsional loading generates compressive/tensile and shear stresses on its plates and stiffened panels. Therefore, a thorough investigation of plates under these combined loads has been carried out. The outcome of this study is interaction diagrams of compression/tension and shear for steel and aluminium plates. The ultimate strength of the structure is then estimated for an applied amount of torsion calculating the shear flow distribution of the plates in the cross section and using the results of the previous study. The same procedure is repeated for different amounts of torsion and the interaction diagram of vertical/horizontal bending moment and torsional moment is derived. For validation, the proposed method is applied to a number of different intact box girders and to a hull girder of a 10000 TEU containership. The effect of damage on the ultimate strength is examined only under bending due to the current representation of damage in the simplified method. The results are compared with the results of non‐linear finite element models which have been generated and analysed for this purpose. The results for all studies show very good correlation, however the simplified method provides a sufficient advantage of time estimation and simplicity in comparison with the existing methods. It can be used in both concept and preliminary design to provide accurate estimation of hull girder strength. This extension of the Simplified Progressive Collapse Method, which accounts for combined load effects, is particularly useful in cases which require quick estimate of ultimate strength.

Includes bibliographical references (leaves 40-43).
In many of the small communities of South Africa's West Coast, the economic driver has traditionally been the fishing industry. Employment opportunities were largely located either on board the vessels or in a fish-processing factory which in some smaller centres was a monopsonistic employer. The last two decades have seen this system under threat. Fish stocks have declined and fish populations have move southward, while the fishing industry has been restructured to meet BEE imperatives, meaning that old established firms found their quotas even further decreased. To cut costs, fishing companies shed jobs and in extreme cases shut down their smaller operations. As they left the smaller centres they took with them their managerial skills, as well as capital and employment. The fishermen and women in these towns, have found it difficult to fill the vacuum, lacking as they do, organisation, access to credit, administrative and marketing skills, and above all critical information related to the process of issuing fishing rights (Isaacs, 2006, 57), (Amason & Kashorte, 2006, 48). The decline of the West Coast fisheries was latterly accompanied by the extension of the permit process; access to the resource being restructured initially in a 'medium term' and then in a long term rights application process. Those fishermen who were unsuccessful in acquiring access rights were trapped in a cycle of poverty and increasingly forced to fish illegally or 'poach' to survive. The decline of the stock means that there are no simple answers to the problem, I argue however, that it would be beneficial for the South African Government to embark on a co-management programme with these fishing communities.

This thesis relies on a Langrangian framework used for conservative tracer transport simulations through 2-D heterogeneous porous media. Conducted numerical simulations enable large sets of concentration values in both spatial and temporal domains. In addition to the advection, which acts on all scales, an additional mechanism considered is local scale dispersion (LSD), accounting for both mechanical dispersion and molecular diffusion. The ratio between these two mechanisms is quantified by the Peclet (Pe) number. In its base, the thesis gives answers to contaminant concentration features when influenced by: i) different log-conductivity variance; ii) log-conductivity structures defined by the same global variogram but with different log conductivity patterns cor-related; and iii) for a wide range of Peclet values. Results conducted by Monte Carlo (MC) analysis show a complex interplay between the aforementioned pa-rameters, indicating the influence of aquifer properties to temporal LSD evolu-tion. A stochastic characterization of the concentration scalar is done through moment analysis: mean, coefficient of variation (CVC), skewness and kurtosis as well as through the concentration probability density function (PDF). A re-markable collapse of higher order to second-order concentration moments leads to the conclusion that only two concentration moments are required for an accurate description of concentration fluctuations. This explicitly holds for the pure advection case, while in the case of LSD presence the Moment Deriv-ing Function (MDF) is involved to ensure the moment collapse validity. Fur-thermore, the expected mass fraction (EMF) concept is applied in groundwater transport. In its origin, EMF is function of the concentration but with lower number of realizations needed for its determination, compared to the one point PDF. From practical point of view, EMF excludes meandering effect and incorporates information about exposure time for each non-zero concentration value present. Also, it is shown that EMF is able to clearly reflect the effects of aquifer heterogeneity and structure as well as the Pe value. To demonstrate the uniqueness of the moment collapse feature and ability of the Beta distribution to account for the concentration frequencies even in real cases, Macrodisper-sion Experiment (MADE1) data sets are used.

QC 20131104

unto L’anguilla europea, Anguilla anguilla L., è una specie catadroma e semelpara che vive quasi tutta la sua vita negli ambienti di acqua dolce, di transizione o di mare costieri (stadio di anguilla gialla). E’ presente, sebbene per poco tempo, anche in ambienti oceanici, infatti quando raggiunge la maturità sessuale allo stadio di anguilla argentina, gli individui iniziano a migrare dai sistemi di acqua dolce o marini costieri e di transizione, raggiungono il Mar dei Sargassi (Oceano Atlantico) per compiervi l’accoppiamento e la deposizione delle uova da parte delle femmine e successivamente gli animali muoiono. Le larve, allo stadio di “leptocefalo”, utilizzando le correnti oceaniche del Oceano Atlantico, compiono il percorso inverso raggiungendo le coste europee dove con una ulteriore metamorfosi si trasformano in “cieche” che si portano negli ambienti di transizione o di acqua dolce. I dati sugli stock giovanili indicano in modo inequivocabile un marcato declino durante gli ultimi quarant’anni, questo è vero non soltanto per A. anguilla, ma anche per A. rostrata L. (l’anguilla americana) e l’A. japonica T. & S. (l’anguilla giapponese). La pesca dell’anguilla nelle Valli di Comacchio (Italia, Nord Adriatico), dove è presente una delle più antiche tradizioni di pesca organizzata dell’anguilla al mondo, dimostra largamente questo declino. Prendendo in esame e mettendo a confronto i dati di A. anguilla a Comacchio, da periodi passati di analisi e dati di raccolte effettuate nel 2011-2012, oltre che dati di letteratura, sono state svolte le ricerche inerenti la tesi di dottorato con i seguenti obbiettivi: a) Sviluppare una nuova relazione lunghezza-peso (LWR) e una nuova relazione lunghezza –età (LAR) per Anguilla anguilla della Valle di Comacchio sulla base dei dati raccolti nel 2011, e confrontarle con le relazioni descritte in precedenza in bibliografia . b) Sviluppare un modello dimensione-età con metodi Bootstrap e Bayesiano per la comprensione della dinamica di popolazione dell’anguilla in una laguna semichiusa, ed applicare il modello medesimo alla popolazione di Comacchio. c) Analizzare una serie di lungo termine sulla produzione di A. anguilla a Comacchio, ed analisi della bibliografia per identificare il ruolo sia al livello locale sia al livello globale, delle varie tipologie di stress sul collasso della popolazione. d) La maggior parte della tesi utilizza modelli matematici relativi alla dinamica della popolazione di anguilla e alle caratteristiche morfometriche. Tali modelli consistono di molte funzioni bivariate che descrivono attributi isolati delle popolazioni. Per questo motivo è stato aggiunto nella tesi un ulteriore capitolo teorico che riporta una review della letteratura e una sintesi di vari tipi di molte funzioni che possono essere usate per risolvere problemi ecologici, ambientali o più genericamente biologici. I risultati della tesi evidenziano che lo stock di Anguilla di Comacchio presenta circa il 99% di femminilizzazione, questo probabilmente legato alla riduzione del numero degli individui della popolazione. L’analisi della relazione LWR mostra che questa non viene influenzata dalla riduzione del numero degli individui della popolazione e si avvicina a quanto stimato alla fine degli anni Settanta prima del crollo della popolazione. Invece LAR viene influenzata dalla riduzione numerica sì da ridurre le classi di età e di conseguenza i tassi di maturazione risultano più veloci (anguille argentine più giovani, più lunghe e più pesanti prima della loro migrazione). Il modello dimensione-età è stato calibrato con i dati 2011 ed ha restituito una curva di sopravvivenza, un valore di stock, di tasso di reclutamento e un tasso di metamorfosi (da gialla ad argentina) per la popolazione di Comacchio. Il modello è stato validato con successo usando i dati 2012. L’approccio modellistico includeva un metodo di correzione degli errori dovuti alla dimensione delle maglie delle reti, mentre una nuova funzione bivariata per la stima della curva di sopravvivenza è stata inserita nel modello. Il procedimento di bootstrap era utilizzato per valutare il livello di incertezza per ogni parametro inserito nel modello utilizzando gli intervalli 95% della distribuzione “highest posterior density” (approccio Bayesiano). Lo stock stimato e il reclutamento del modello erano almeno dieci volte più bassi delle stime rispettive ottenute in precedenti studi usando dati della fine degli anni ’80 mettendo in evidenza lo stato cruciale della popolazione. I dati di produzione di anguille argentine dalle Valli di Comacchio, che equivale alla totalità degli individui migranti, copre il periodo dal 1781 al 2013, e costituisce la più lunga raccolta di dati annuale al mondo per la pesca di uno specifico tipo di pesce. I dati includono anche informazioni sulla perdita di habitat e di altri fattori di stress per la popolazione (i.e. temperature molto basse, ipersalinità, inondazioni, inquinamento, ecc.). Il ruolo dei fattori di stress locali sono stati analizzati come causa del declino della popolazione, mentre informazioni addizionali, provenienti dalla letteratura, venivano anche usate e discusse per verificare effetti di stress di tipo globale (i.e. raccolta di cieche a scopi acquacolturali, cambiamenti climatici oceanici, perdita di habitat, inquinamento e parassitismo) su tre differenti specie di anguilla, A. anguilla, A. rostrata e A. japonica. Il collasso della popolazione nelle Valli di Comacchio, che ha avuto inizio negli anni ’70, non mostra segni di possibile recupero, e non può essere spiegato dagli stress di tipo locale. La letteratura relativa agli stress di tipo globale, suggerisce che le tre specie di anguille, subiscono l’effetto combinato di più fattori negativi. L'acquacoltura, che dipende interamente dalle cieche catturate in natura, svolge un ruolo chiave nel declino degli stock naturali. La relazione fra produzione da acquacoltura europea rispetto alle rese delle Valli di Comacchio ed altri dati pubblicati dimostrano, nella riduzione delle popolazioni, il ruolo chiave delle catture di cieche a scopi acquacolturali. Stime conservative fatte usando dati FAO, mostrano che la quantità corrente di cieche necessarie a sostenere la produzione acquacolturale in Europa e in Asia è di circa 2x109 individui. Questa domanda, largamente soddisfatta da cieche di specie Anguilla anguilla, può giustificare il marcato declino della specie, in quanto il mercato delle cieche si è espanso a livello internazionale. Un ultimo studio teorico ha prodotto un totale di 20 modelli che possono descrivere curve a campana simmetriche e non, curve convesse o semplici sigmoidi (tipo curva di crescita con saturazione), curve doppio sigmoidi (tipo curva di crescita con saturazione), curve bilineari e periodiche. I modelli possono anche essere modificati per descrivere la relativa variazione di una variabile dipendente (range della variabile dipendente fra 0 e 1). Sono state anche prodotte linee guida aggiuntive su come creare una curva specchio basata su ognuno dei 20 modelli.
The European eel (Anguilla anguilla L.) is a catadromous and semelparous species that spends most of its life in fresh water, brackish and coastal habitats (yellow eel stage). When reaching maturity passes to the silver eel stage and migrates to the Sargasso Sea (Atlantic Ocean) in order to spawn and die. The larvae (leptocephalus) drift back using oceanic currents and metamorphose into transparent glass eels when they reach the European coastlines. Records of juvenile stocks indicate a tremendous decline during the last four decades not only for A.anguilla but also for other important eel species like the American eel (Anguilla rostrata L.) and the Japanese eel (Anguilla japonica T. & S.). The eel fishery in the Comacchio Lagoon (Italy), which is one of the oldest organized eel fisheries in the world, also faces large stock decline. Taking into account data about A.anguilla in Comacchio from older surveys and surveys performed during 2011-2012 and other information from the international literature, the following objectives were set in the context of the thesis: a) Development of new length-weight (LWR) and length-age (LAR) relationships of A.anguilla from the Comacchio Lagoon using data of 2011 and comparison with previous surveys. b) A size-age model development based on bootstrapping and Bayesian approaches for the assessment of eel population dynamics in semi-closed lagoons and application of the model for the Comacchio population. c) Analysis of the long-term series of A.anguilla production in the Comacchio and conducting a literature review and analysis about the contribution of local and global stressors on the population collapse. d) The major part of the thesis deals with mathematical models related to eel population dynamics and morphometric characteristics. Such models consist of many bi-variate functions which describe isolated attributes of the populations. For this reason, a supplementary theoretical chapter was included in the thesis and concerns the literature review and synthesis of various types of such functions which can be used in ecological, biological and environmental problems. The results of the thesis showed that the eel stock of Comacchio has undergone 99% feminization, probably due to the population density reduction. The analysis of LWR showed that it was not affected by the reduction of population density and approximates the estimated ones of the late seventies before population collapse. On the other hand, LAR was affected leading to age classes reduction and consequently faster maturation rates (younger, longer and heavier silver eels before their migration). The size-age model was calibrated using the data of 2011 and assessed the survival curve, stock, recruitment and metamorphosis rates (from yellow to silver) of Comacchio population. The model was successfully validated using data from 2012. The modeling approach included a method for correcting errors inserted by net selectivity while a new bi-variate function for estimating survival curve was also incorporated. A bootstrap procedure was used to assess the level of uncertainty for each model parameter using the 95% intervals of the highest posterior density distribution (Bayesian approach). The estimated stocks and recruitment by the model were at least ten times lower from the respective estimations of previous studies using data from the late 80s highlighting the crucial state of the population. The data for the silver eel production from Comacchio Lagoon (equivalent to the total migrating population) cover the period 1781-2013 and constitute the longest annual records in the world about the fishery of the specific fish species. The data include information related to habitat loss and other local stressors of the population (e.g. frost, hypersalinity, floods, pollution events etc). The role of the local stressors on the decline of the local stock was investigated while additional information from the literature was also used to discuss the effects of global stressors (e.g. glass eel harvest for aquaculture, climate-oceanographic changes, habitat loss, pollution and parasitism) on the three eel species A.anguilla, A.japonica, A.rostrata. The population collapse in Comacchio, which started in the ‘70s with no signs of recovery, could not be explained by local stressors. The literature about the global stressors suggested that the three eel species are under a combined threat from various directions. Aquaculture, which depends entirely on wild-caught glass eels, was found to play a key role in the decline of natural stocks. The correlations between European aquaculture production versus the Comacchio yields and other published data from other European eel and glass eel fisheries were found significantly high exposing the crucial role of aquaculture. Conservative estimations using FAO data showed that the current amount of glass eels needed to support aquaculture production in Europe and Asia exceeds the 2×109 specimens. This demand, largely covered by A. anguilla glass eel, can justify eel populations decline since glass eel trade has been expanded at international level. The supplementary theoretical study provided a total of 20 models which can describe symmetric and non symmetric bell-shaped curves, convex and simple sigmoid curves (saturation-growth type), double sigmoid curves (saturation-growth type), bilinear and periodical curves. The models were also modified in order to describe the relative variation of a dependent variable (range of dependent variable between 0-1). Additional guidelines were also provided on how to create a mirror curve based on each one of the aforementioned 20 models.

Les ruisseaux couverts sont d’anciens tunnels maçonnés à vocation hydraulique, recouverts de stériles miniers au-dessus desquels différentes infrastructures ont été construites. De récents effondrements posent aujourd’hui la problématique de l’estimation du risque d’effondrement de ces ouvrages. Dans cette thèse, nous avons tenté de proposer une méthodologie permettant de répondre à cette problématique. Du fait de l’intensité du phénomène étudié, l’étude s’est concentrée sur la détermination de la probabilité d’occurrence et sur les enjeux.L’utilisation de la méthode multicritère AHP a permis de proposer une note de risque à partir des enjeux et des désordres en présence. Du fait de l’incapacité du modèle à estimer rétroactivement les effondrements relevés sur 28 ouvrages, l’étude s’est par la suite concentrée sur l’estimation de la probabilité d’occurrence des effondrements.Une analyse statistique a permis d’estimer que les effondrements rencontrés dans ces ouvrages étaient liés à l’effondrement des piédroits (83% des cas) et à l’effondrement de la sortie des ouvrages (17% des cas). L’utilisation de la méthode de la régression logistique a permis, à partir de paramètres géométriques et de désordres observés, d’estimer rétroactivement et avec un F1-score moyen de 84% la probabilité d’occurrence de ces deux types d’effondrement.Afin de prendre en compte la dégradation des propriétés mécaniques des maçonneries, nous avons proposé un méta-modèle d’estimation du coefficient de sécurité des piédroits à partir de modèles numériques. L’approche a été évaluée rétroactivement et a permis d’obtenir un F1-score de 82%.Une combinaison des approches a ensuite été utilisée pour estimer le risque effondrement de 28 ouvrages découpés virtuellement en 180 tronçons. La méthodologie développée et les résultats obtenus pourront permettre de prioriser des actions préventives (réparations d’ouvrages, sécurisations de zones potentielles d’effondrement et mise en sécurité des personnes)
Covered stream tunnels are old masonry hydraulic tunnels, covered with tailings, over which various infrastructures were constructed. Recent and unforeseen collapses have raised the issue of the lack of knowledge on the risk assessment of these tunnel collapses. In this thesis, we have proposed a methodology to tackle such an issue. Because of the intensity of the phenomenon, the study focused on determining the probability of occurrence of this identified hazard and the stake value.The application of the multi-criteria analysis enabled to propose a risk-scoring model based on the issues and the disorders involved. As the model fails to retroactively predict the collapses observed on 28 structures, the study then focused on estimating the probability of the collapse occurrence.A statistical analysis has enabled us to estimate that the collapses encountered in these tunnels were related to the collapse of the sidewalls (83% of the total number of collapses) and the tunnel exit collapse (17% of the total number of collapses). The application of the logistic regression method, by using the geometrical features and the disorders observed in-situ, enabled to evaluate retroactively, with an average F1-score of 84 %, the probability of occurrence of these two types of collapses.In order to consider the degradation of the mechanical properties of masonry, we have proposed a meta-model that could estimate a safety coefficient of the sidewalls from numerical models. The approach was evaluated retroactively and resulted in an F1 score of 82%.All of these approaches were then aggregated and used to assess the collapse risk of 28 underground tunnels virtually divided into 180 sections. The methodology developed and the results obtained will enable us to prioritize preventive actions (structural repairs, securing potential areas of collapse and securing people)

La cavitation est la formation de bulles de vapeur dans un liquide statique ou en écoulement. L’érosion de cavitation se produit quand ces bulles collapsent à cause de la récupération de pression. Ce phénomène peut endommager les parois à proximité desquelles les bulles collapsent. Il s’agit d’un problème majeur dans les machines hydrauliques. Par exemple, les turbines hydrauliques fonctionnent aujourd’hui souvent dans des régions défavorables du point de vue de la cavitation, pour réguler le réseau électrique. Mesurer la cavitation et le taux d’érosion est souvent très difficile voire impossible. L’émission acoustique (EA) est une méthode qui permet la mesure de cavitation sans accès direct à l’écoulement ; toutefois, les données sont difficiles à interpréter. Cette thèse présente quelques possibilités de traitement des données de l’EA pour quantifier les diamètres des indentations créées par impacts individuels de la cavitation et aussi pour évaluer l’érosion de cavitation. De plus, les taux d’érosion de trois matériaux d’aubes de turbine Francis ont été caractérisés. Les raisons pour les différences dans le taux d’érosion de deux aciers inoxydables et martensitiques sont analysées. Tous les essais de cavitation ont été réalisés dans le même tunnel de cavitation haute vitesse. Un premier résultat majeur de cette thèse est le développement d’une méthode pour compter les pics d’EA par une technique d’enveloppe du signal. Les distributions cumulées des pics d’EA sont comparées à celles des diamètres d’indentations. Une relation est proposée entre l’amplitude des pics d’EA et le diamètre des indentations. Le deuxième résultat majeur est le lien entre l’évolution de l’érosion de cavitation et la fréquence de lâcher des nuages de cavitation. Bien que les signaux d’EA soient mesurés en haute fréquence, un processus de démodulation a été mis en œuvre qui permet de mettre en évidence la basse fréquence de lâcher. Cette fréquence augmente avec la rugosité et la déformation de surface au fur et à mesure de la progression de l’endommagement. Par ailleurs, les raisons entre les différences de taux d’érosion des aciers inoxydables et martensitiques ont été identifiées : la taille des grains d’austénite initiale, les tailles des plaques et plaquettes et la quantité d’austénite résiduelle sont les principaux facteurs influants. Cette thèse propose plusieurs résultats directement utilisables, comme la classification entre les aciers inoxydables martensitiques, ainsi que des méthodes pour surveiller la cavitation mises au point en laboratoire dans un tunnel de cavitation et potentiellement applicables aux machines hydrauliques. Le résultat majeur est que l’EA a un fort potentiel pour surveiller la cavitation et l’érosion de cavitation avec l’avantage important qu’elle ne nécessite pas d’accès direct à l’écoulement
Cavitation is the formation of vapor bubbles either in a static liquid or in a liquid flow due to a drop in static pressure. When these bubbles collapse, as a result of pressure recovery, they may damage adjacent surfaces. These events are major causes of damage and nuisance in hydro machines. Modern hydro turbines are often used to regulate power grids; therefore, they may be operated out of their designed range. The flow-related optimal operation is different from the economic optimal usage. Detecting and characterizing cavitation and assessing damage during operation can be difficult or even impossible. Acoustic emission (AE) measurements provide a way to measure cavitation without access to the flow, but interpreting the data is challenging. This thesis presents insights in the ways of treating the AE data both in characterizing individual pits created by cavitation impacts and in tracking the evolution of cavitation erosion. Additionally, the erosion rates of three turbine materials were compared, and the main reasons behind the differing erosion rates of two martensitic turbine steels were discovered. The same high-speed cavitation tunnel was used in all cavitation experiments. This thesis firstly presents a method for enveloping an AE waveform signal and for counting the peak voltage values. The resulting cumulative distributions were compared to those of cavitation pit diameters, and from this comparison, a connection was proposed between AE peak voltage value and pit diameter. The second result was the connection between cavitation cloud shedding frequency and erosion evolution. The process of demodulating high frequency AE signals effectively promotes the low frequency shedding. The shedding frequency increased with accumulating material loss, and it was concluded that this increase is due to geometry effects, namely surface roughness. In addition to the two proposed methods, it was found that the decisive factors in the differing erosion rates of the martensitic stainless steels are the prior austenite grain size, packet and block sizes and the retained austenite fraction. This thesis provides guidelines directly applicable, such as the martensitic steel classifying, and methods that require further development, if one wishes to utilize them in hydro machine cavitation monitoring instead of laboratory measurements in a cavitation tunnel. The main outcome is that AE is a potential way to monitor cavitation, with the important benefit of not requiring any access to the flow

Pastaruosius du dešimtmečius Lietuvoje ir kitose šalyse aukštojo mokslo kokybei skiriamas vis didesnis dėmesys, tačiau Lietuvoje nėra atlikta sisteminių tyrimų apie kolegijų veiklos kokybės išorinio institucinio vertinimo patirtį ir rezultatus, dar daugiau – vertinimo procedūrų ir turinio tobulinimas vyksta epizodiškai ir iš dalies pagrįstai. Tyrimo objektas – kolegijų veiklos kokybės išorinio institucinio vertinimo sandara, akcentuojant išorinio vertinimo procedūras. Tyrimo tikslas - teoriškai pagrįsti ir empiriškai patikrinti kolegijų veiklos kokybės išorinio institucinio vertinimo proceso (analizuojant tik taikomas vertinimo procedūras) modelį ir nurodyti studijų kokybės vertinimo proceso tobulinimo kryptis. Magistro darbe yra apibrėžiamos kolegijų išorinio institucinio vertinimo ir įvertinimo sampratos, analizuojant kolegijų paskirtį; kolegijų veiklos kokybės koncepcijas; vertinimo ir įvertinimo procesus; vertinimo tipus; institucinio vertinimo vietą ir reikšmę aukštojo mokslo vertinimo sistemoje; sąsajas tarp vidinio ir išorinio vertinimo bei vertinimo principus. Šiame darbe aptariamos Europos aukštojo mokslo kokybės užtikrinimo nuostatos, kurios jau yra pradėtos diegti daugelyje Europos šalių, tame tarpe ir Lietuvoje. Analizuojamos aukštųjų mokyklų išorinio kokybės vertinimo sistemos Europos šalyse, atpažįstami šiose sistemose taikomi bendrieji Europos aukštojo mokslo kokybės užtikrinimo principai. Apibendrinama kolegijų išorinio institucinio vertinimo... [toliau žr. visą tekstą]
Attention to the quality of higher education has considerably increased in Lithuania and other countries during the last two decades. The systematic research on the experience of external institutional quality assessment of colleges still has not been executed in Lithuania. Furthermore the improvement of the procedures and the content of assessment is episodic and poorly based. The master theses define the conception of external institutional quality assessment of colleges and the decisions taken after their assessment; the conceptions of colleges’ quality, the processes of evaluation and assessment, the types of assessment, the place and the meaning of institutional assessment in the context of higher education assessment system, the links between internal and external assessment; the fundamentals of assessment. The master theses deal with the discussion of the European Standards for quality assurance in higher education. These standards in a number of European countries including Lithuania are under development and the common principles of European quality assurance in higher education have been analyzed. The experience in external institutional quality assessment of colleges have been summarized and the model of the process of external quality assessment of colleges have been provided. The model that has been analyzed consists of 5 main stages: 1) preparation for external assessment; 2) analysis and evaluation of self-assessment documents; 3) visit to the institution... [to full text]

碩士
中華科技大學
土木防災工程研究所
99
The progressive damage of the steel moment resisting frame building is conducted in this research. The feature of this is investigated with a nine-story moment frame prototype building. The loss column scenario leads to develop the plastic hinges of beams and columns having addressed accordingly. The vulnerability of frames due to sudden column removal is performed with a nonlinear pushover analysis. The capacity curves of the nonlinear pushover analysis and the configurations of plastic hinges are constructed to identify the risk of the progressive damage. An extensive nonlinear time history analysis is conducted to trace the stress propagating path. The various number of column loss includes interior and exterior columns on the different stories. The corresponding fragility curves are achieved with the maximum likelihood method as a design reference for essential structures.

The issue of progressive collapse has been trending since it's connected with uncertainties that can make it difficult to accurately assess a structure's safety. The purpose of the current is to perform bibliometric analysis along with literature review of progressive collapse and execute progressive collapse analysis of a seven-storey RC building in SAP2000 and study the influence of different parameters of the building. In this study nonlinear dynamic analysis coupled with response surface methodology (RSM) is employed to investigate progressive collapse of a seven-storey RC building. For nonlinear dynamic approach of progressive collapse, structural analysis software SAP2000 is used. In response surface, Box–Behnken design is employed to analyse the progressive collapse of the structure with three positions of column elimination i.e. corner, middle and penultimate position. The current study considered three independent input variables namely grade of concrete, length and depth of beam with three levels and deflection of beam is taken as a response. Based on the ANOVA results, all three input parameters have substantial impact on the response in each of the three positions of column elimination. In each case RSM fits quadratic model for deflection of beam with confidence interval of 95%. The response calculated using the generated model is found to be quite close to the actual readings. The main effects plots are not horizontal line which describes the significance of individual factors with different levels on the response. Results shows that with the increase in the values of grade of concrete and depth of beam, the vertical v deflection of the upper node of column removal point decreases whereas increase in beam length increases the deflection. The interaction effect of different factors, grade of concrete versus beams length and beam depth versus beam length, is significant in corner column elimination. But in middle column elimination case, the interaction effect of beam length versus depth is close to significant while no interaction effects are found significant in penultimate column removal case. The values of grade of concrete and beam depth should be in the higher range and beam length should be in the lower range to get the optimal response. It also covers limitations and future research of the current study.

碩士
國立成功大學
土木工程學系
105
The casualty risk and social impact caused by the collapse of these buildings should not be underestimated. Furthermore, if mid-rise buildings of critical facilities, e.g. hospital, high-tech factory etc., were damaged during earthquakes will also cause great economic loss. Therefore, developing suitable assessment methods to identify seismic performance levels and collapse risk of these buildings become a critical issue. Even though traditional seismic assessment methods, which usually employ the nonlinear static pushover analysis, have been successfully applied to regular low-rise buildings, these methods are unable to reflect higher-mode effect on the responses of mid-rise buildings. Furthermore, a traditional approach usually leads to a deterministic result that could not account for the uncertainty in seismic motions and structural responses of a mid-rise building, which is usually more complicated and involves more structural uncertainties than a low-rise building. For this reason, this paper presents a procedure to assess the risk of collapse and various seismic performance levels for mid-rise buildings based on the methodology proposed by FEMA P-58 and also acceptance criteria suggested in ASCE 41-13 and FEMA 356. To establish the fragility curves, this approach employs nonlinear time history analysis together with the method of incremental dynamic analysis (IDA) to estimate structural response parameters. For demonstration, the proposed approach is applied to assess the seismic risk of a mid-rise building that collapsed in the Meinong earthquake (2016) for various performance levels. In addition, the collapse risk of the building was assessed by using the proposed method and then compared with the observation in the Meinong earthquake.

碩士
國立臺灣海洋大學
河海工程學系
107
Taiwan is surrounded by the ocean and the plain area is small. With the population growth in the past, the demand for land development is increasing. To achieve the balance between the land utilization and demands, it must develop more slope lands. In addition, because of the climate change in recent year, the extreme rainfall frequently happened, such as rainfall strength and duration. Moreover, it caused the collapse of Taiwan’s mountainous areas to increase the risk of neighboring slope communities and roads. In the past, domestic and foreign research focused on the hazard for slope land disasters, and less risk assessment of the overall risk of slope disasters. Therefore, this study is adopted a definition of disaster risk is function of hazard and vulnerability by the UNISDR (United Nations International Strategy for Disaster Reduction). In addition to the spatial distribution of slope disaster risk, the research scale uses village level to explore the risk of shallow collapse in the slopes of Keelung City. In this study, the hydrological model - topographical index model of the topographical characteristics of the basin area is used to calculate the relationship between the topography and the groundwater level. And the stability analysis of the infinite slope is used to investigate the influence of different groundwater level heights on the slope land stability of the study area. The slope land collapse factor is summarized as the hazard aspect of the study. Meanwhile, the research area is affected by the vulnerability of the slope land disaster, with the social, economic, environmental, physical aspects, and the resilience is added to vulnerability index. Vulnerability factors such as vulnerable population, population density, road density, disaster record, household income, disaster temporary shelters were selected. The vulnerability analysis was performed using the Pareto Ranking method. The calculated hazard map and the vulnerability map are combined with the risk matrix to evaluate the slope land risk level and use the Geographic Information System (GIS) to display the risk map. Finally, the risk assessment model for shallow collapse disasters on slope land is established. The risk assessment of shallow collapse on slope land shows that most of the villages are concentrated in the metropolitan area of Renai and Zhongzheng District in Keelung City, while others are in Qidu, Zhongshan and Anle District in the face of the impact of sloping land disasters. Due to their vulnerability are larger than other area, which leads to the situation that the risk level of these villages is "high" to "very high". This study explores the risk of shallow collapse on slope land from the perspective of risk. Compared with the past, it only discusses the hazard orientation of slope land, and can better reflect the relative risk each region. It can effectively focus on high-risk areas for decision-making units in regional risk management.

Dissertação de Mestrado em Construção Metálica e Mista apresentada à Faculdade de Ciências e Tecnologia
Robustness for buildings is a compilation of lessons learned from past experiences in the engineering world. The main purpose is always the same: to avoid the progressive collapse on buildings second to an accidental load like fire, explosion, impact or the consequence of a human error. This is why the construction norms for Europe, EN 1991 part 1-7, is focused in that matter. However, preparing a building to withstand the additional stress caused by these events, can make the final cost of the structure out of reach for the investor. This is what motivated the research at hand, so that we could design a structure, on top of the building, capable of redistributing the loads.In order to reach this objective, a parametric numeral study was done, where two buildings were designed under three different conditions. The first one was a simple structural design following the consideration on the European norms for ultimate and serviceability limit state, used as a refence point. On the second one, the buildings were design following the Eurocode 1 part 1-7 for accidental load, making the structure with enough redundancy in order to tolerate the stress applied. On the third one, the latter was applied by using a super-structure to redistribute the load. The solutions were compared based on the final weight and connection rigidity of the building. On both cases the building with the super structure was verified for the accidental combination loads. However, the smaller one, when checked for normal conditions for the ULS and SLS, was not satisfactory, having to be redesigned for the additional weight of the super structure.Making a comparison of the final solution for both buildings, we arrived at the conclusion that the super-structure that was considered, helped the structural design. Even though for the smaller building the solution was not lighter, the connection rotational stiffness was considerably lower, whereas for the second building, both conditions were satisfactory.
Robustness for buildings is a compilation of lessons learned from past experiences in the engineering world. The main purpose is always the same: to avoid the progressive collapse on buildings second to an accidental load like fire, explosion, impact or the consequence of a human error. This is why the construction norms for Europe, EN 1991 part 1-7, is focused in that matter. However, preparing a building to withstand the additional stress caused by these events, can make the final cost of the structure out of reach for the investor. This is what motivated the research at hand, so that we could design a structure, on top of the building, capable of redistributing the loads.In order to reach this objective, a parametric numeral study was done, where two buildings were designed under three different conditions. The first one was a simple structural design following the consideration on the European norms for ultimate and serviceability limit state, used as a refence point. On the second one, the buildings were design following the Eurocode 1 part 1-7 for accidental load, making the structure with enough redundancy in order to tolerate the stress applied. On the third one, the latter was applied by using a super-structure to redistribute the load. The solutions were compared based on the final weight and connection rigidity of the building. On both cases the building with the super structure was verified for the accidental combination loads. However, the smaller one, when checked for normal conditions for the ULS and SLS, was not satisfactory, having to be redesigned for the additional weight of the super structure.Making a comparison of the final solution for both buildings, we arrived at the conclusion that the super-structure that was considered, helped the structural design. Even though for the smaller building the solution was not lighter, the connection rotational stiffness was considerably lower, whereas for the second building, both conditions were satisfactory.

Dissertação de Mestrado em Construção Metálica e Mista apresentada à Faculdade de Ciências e Tecnologia
Robustness for buildings is a compilation of lessons learned from past experiences in the engineering world. The main purpose is always the same: to avoid the progressive collapse on buildings second to an accidental load like fire, explosion, impact or the consequence of a human error. This is why the construction norms for Europe, EN 1991 part 1-7, is focused in that matter. However, preparing a building to withstand the additional stress caused by these events, can make the final cost of the structure out of reach for the investor. This is what motivated the research at hand, so that we could design a structure, on top of the building, capable of redistributing the loads.In order to reach this objective, a parametric numeral study was done, where two buildings were designed under three different conditions. The first one was a simple structural design following the consideration on the European norms for ultimate and serviceability limit state, used as a refence point. On the second one, the buildings were design following the Eurocode 1 part 1-7 for accidental load, making the structure with enough redundancy in order to tolerate the stress applied. On the third one, the latter was applied by using a super-structure to redistribute the load. The solutions were compared based on the final weight and connection rigidity of the building. On both cases the building with the super structure was verified for the accidental combination loads. However, the smaller one, when checked for normal conditions for the ULS and SLS, was not satisfactory, having to be redesigned for the additional weight of the super structure.Making a comparison of the final solution for both buildings, we arrived at the conclusion that the super-structure that was considered, helped the structural design. Even though for the smaller building the solution was not lighter, the connection rotational stiffness was considerably lower, whereas for the second building, both conditions were satisfactory.
Robustness for buildings is a compilation of lessons learned from past experiences in the engineering world. The main purpose is always the same: to avoid the progressive collapse on buildings second to an accidental load like fire, explosion, impact or the consequence of a human error. This is why the construction norms for Europe, EN 1991 part 1-7, is focused in that matter. However, preparing a building to withstand the additional stress caused by these events, can make the final cost of the structure out of reach for the investor. This is what motivated the research at hand, so that we could design a structure, on top of the building, capable of redistributing the loads.In order to reach this objective, a parametric numeral study was done, where two buildings were designed under three different conditions. The first one was a simple structural design following the consideration on the European norms for ultimate and serviceability limit state, used as a refence point. On the second one, the buildings were design following the Eurocode 1 part 1-7 for accidental load, making the structure with enough redundancy in order to tolerate the stress applied. On the third one, the latter was applied by using a super-structure to redistribute the load. The solutions were compared based on the final weight and connection rigidity of the building. On both cases the building with the super structure was verified for the accidental combination loads. However, the smaller one, when checked for normal conditions for the ULS and SLS, was not satisfactory, having to be redesigned for the additional weight of the super structure.Making a comparison of the final solution for both buildings, we arrived at the conclusion that the super-structure that was considered, helped the structural design. Even though for the smaller building the solution was not lighter, the connection rotational stiffness was considerably lower, whereas for the second building, both conditions were satisfactory.

The process which culminated in the establishment of the East African Community (EAC) in 1967 started in the early 1920s. The idea was first conceived in Britain. Initially, East Africans vehemently opposed this idea fearing that it would sustain British hegemony in the region, but their resentment did not prevent the establishment of the East African High Commission (EAHC) in January 1948. It was only in the 1950s and 1960s that East African leaders embraced the idea due to political and economic reasons. In 1961 they converted the EAHC into the East African Common Services Organisation (EACSO) and in 1967 they established the EAC. Nationalism and sub-nationalisms in the region cast a spell on the EAC. The coup, which took place in Uganda in 1971, strained relations between Idi Amin and Presidents Nyerere and Kenyatta thus making it impossible to hold regional meetings. Eventually, the EAC collapsed in June 1977.
Political Science
M.A. (Politics)

Dissertação de Mestrado em Mecânica dos Solos e Engenharia Geotécnica apresentada à Faculdade de Ciências e Tecnologia
Reservatório Cerro da Mina é um reservatório de águas industriais, parte do complexo mineiro de Neves-Corvo, ao sul de Portugal. Impermeabilizado a montante por uma membrana de PEAD e construído aproximadamente metade em enrocamento e metade em rocha escavada, esta barragem esteve sujeita a três momentos de assentamento abruptos no aterro nos seus primeiros anos de operação. Este comportamento levantou questões acerca da natureza dos movimentos e da possibilidade de algum problema inesperado. A análise dos dados de nove extensómetros e de um inclinómetro instalados na secção de maior altura do enrocamento, juntamente com a avaliação das condições ambientais nos períodos em causa, revelaram que os deslocamentos significativos e inesperados coincidiram com períodos de intensa pluviosidade e subida no nível de água no reservatório. Tanto as deformações verticais como as horizontais apresentaram tendência de aumento acelerado sempre que um novo máximo no histórico de precipitações era registrado. O comportamento observado sugere que o aumento da humidade nos vazios do enrocamento gera uma redução significativa nos valores de sucção nos poros dos elementos rochosos, causando colapsos induzidos por molhagem no enrocamento. Além disso, os dados de observação indicam uma reduzida influência da oscilação do nível de água no reservatório na direção vertical, descartando este fator como causa principal dos assentamentos no enrocamento. As taxas de deformações verticais a longo prazo foram calculadas e apresentaram tendência similar ao previsto para este tipo de estrutura, não demonstrando sinais de problema neste sentido.
Reservatório Cerro da Mina is an industrial water reservoir part of Neves-Corvo mining compound, in the south of Portugal. Covered by an upstream impervious HDPE membrane and constructed approximately half on rockfill embankment and half on excavated rock, this dam experienced three moments of abrupt settlements on its embankments in the first years of operation. This behaviour raised concerns regarding the nature of the movements and the possibility of unanticipated problems. The analysis of the data from nine extensometers and one inclinometer installed in the highest section of the rockfill embankment, along with the assessment of the environmental conditions in the periods of interest, revealed that these significant unexpected vertical displacements coincided with periods of intense rainfall and rise in the water level in the reservoir. Both vertical and horizontal deformations of the rockfill showed a tendency of sudden increase when a new maximum in the precipitation record occurred. This represents an indication that the increase in humidity in the rockfill voids led to a significant decrease in the rock pore suction, causing wet-induced collapses in the rockfill. Additionally, the influence of the oscillation of the water level reservoir was estimated very small in the vertical direction, rejecting this factor as a major source of settlements in the rockfill. Long-term vertical deformation rates in the rockfill were calculated and presented a tendency fairly similar to what is expected for the kind of construction, showing no evidences of problems in that matter.

It is important to be able to accurately assess seismic risk so that vulnerabilities can be prioritized for retrofit, emergency response procedures can be properly informed, and insurance rates can be sustainably priced to manage risk. To assess the risk of a building (or class of buildings) collapsing in a seismic event, procedures exist for creating one or more mathematical models of the structure of interest and performing nonlinear time history analysis with a large suite of input ground motions to calculate the building's seismic fragility and collapse risk. In this dissertation, three aspects of these procedures for assessing seismic collapse risk are investigated for the purpose of improving their accuracy.

It is common to use spectral acceleration with a damping ratio of 5% as a ground motion intensity measure (IM) for assessing collapse fragility. In this dissertation, the use of 70%-damped spectral acceleration as an IM is investigated, with a focus on evaluating its sufficiency and efficiency. Incremental dynamic analysis (IDA) is performed for 22 steel moment frame (SMF) models with 50 biaxial ground motion records to formally evaluate the performance of 70%-damped spectral acceleration as an IM for highly nonlinear response and collapse. It is found that 70%-damped spectral acceleration is much more efficient than 5%-damped spectral acceleration and much more sufficient with respect to epsilon for all considered levels of highly nonlinear response. Its efficiency and sufficiency compares also compares well with more advanced IMs such as average spectral acceleration.

When selecting input ground motions for nonlinear time history analysis, most engineers select ground motion records from the NGA-West2 database, which are processed with high-pass filters to remove long-period noise. In this dissertation, the extent to which these filters remove actual ground motion that is relevant to nonlinear time history analysis is evaluated. 52 near-source ground motion records from large-magnitude events are considered. Some records are processed by applying high-pass filters and others are processed by record-specific tilt corrections. Raw and NGA-West2 records are also considered. IDA is performed for 9-, 20-, and 55-story steel moment frame models with these processed records to assess the effects of ground motion processing on the calculated collapse capacity. It is found that if the cutoff period (Tc) is at least 40 seconds, then applying a high-pass filter does not have more than a negligible effect on collapse capacity for any of the considered records or building models. For shorter Tc (e.g. 10 or 15 seconds), it is found that the filters sometimes have a large effect on calculated collapse capacity, in some cases by over 50%, even if Tc is much larger than the building’s fundamental period. Of the considered ground motions, simply using the raw, uncorrected records usually yields more accurate results than using ground motions that have been processed with Tc less than or equal to 20 seconds.

For an existing building with unknown design plans, one might perform a collapse risk assessment using an archetype model for which the specific member sizes are assumed based on the relevant design code and building site. In this dissertation, the sensitivity of seismic collapse risk estimates to design criteria and procedures are evaluated for six 9-story and four 20-story post-Northridge SMFs. These SMFs are designed for downtown Los Angeles using different design procedures according to ASCE 7-05 and ASCE 7-10. Seismic risk analysis is performed using the results of IDA with 44 ground motion records and the results are compared to those of pre-Northridge models. It is found that the collapse risk of 9-story SMFs designed according to performance-based design vary by 3x, owing to differences in GMPEs used to generate site-specific response spectra. There is generally less variation in the collapse risk estimates of 20-story post-Northridge SMFs when compared to 9-story post-Northridge SMFs because wind drift limits control the design of many members of the 20-story SMFs. Differences in collapse risk between pre- and post-Northridge SMFs are found to be at least 4x and 8x for the 9- and 20-story models, respectively. Furthermore, in response to four strong ground motion records from large-magnitude events, some of the 9-story and all of the 20-story pre-Northridge SMFs experience collapse and most of the post-Northridge SMFs experience significant damage (MIDR > 0.03).

碩士
國立中央大學
土木工程研究所
96
A series of centrifuge modeling tests were performed to study the effect of collapse of the adjacent constructing pile and the groundwater lowering on the existed pile in saturated sandy ground. Two topics are investigated. The first is the effect of the collapse of constructing pile on the existed pile. The second is the changes of axial force and settlement on the existed pile and the variation of the ground surface settlement as a result of different groundwater withdraw level. The test results show that, at the self-weight consolidation stage, the settlement of the soil is greater than that of the existed pile and the neutral point of pile in all the tests is located at near the pile tip, leading to the axial force of existed pile increases with the increasing depth. In the next stage while the work load was applied on the existed pile head, the settlement of the existed pile is greater than that of the soil resulting in the positive skin friction developed along the pile. When the distance between the existed and the constructing piles is 1.5 m, the collapse of constructing pile leads to the significant changes of the axial force within the existed pile and the occurrence of the negative skin friction along the existed pile. But it would disappear when the distance of piles is 3 m. Besides, the collapse of constructing pile leads to the decrease in the skin friction of the existed pile because of the decrease in the lateral earth pressure, and so does the lowering groundwater level resulting from the increase in the axial force. In addition, the measured ground surface settlement, skin friction and axial force of pile are in good agreement with that obtained from the theoretical analysis. The estimated Young’s modulus Es at each stage of testing procedure also corresponds with that proposed in the past studies.