1,721,021 research outputs found
Propagation and band width of smeared cracks
No full textThe crack band approach (in the smeared crack concept) is widely used for the modeling of concrete fracture and is an important analysis technique within advanced engineering. However, the simulations can be impeded by mesh-induced directional bias. Cracks prefer to propagate along continuous mesh lines, which causes a dependency of the numerical results on the structure and orientation of the finite element discretization. In this PhD research, two different enhancements of the crack band approach are proposed to reduce the mesh bias as much as possible. The performance of both enhancements is investigated by simulations of plain concrete fracture tests and a shear critical reinforced concrete beam without shear reinforcement. Both enhancements increase the accuracy of the crack band approach in the smeared crack concept and simultaneously preserve its relative simplicity. Hence, they can be valuable for engineering practice, supporting reliable predictions of ultimate load capacities, failure mechanisms and post-peak behaviors of quasi-brittle reinforced concrete structures.Structural EngineeringCivil Engineering and Geoscience
Fragile yet Ductile: Structural Aspects of Reinforced Glass Beams
No full textThis dissertation investigates the structural aspects of reinforced glass beams. The concept of these beams, which are intended for building applications, is to provide redundancy even if the glass is broken. This redundancy is obtained through a small reinforcement section that is bonded at the tensile edge of the glass beam. Upon glass failure the reinforcement section bridges the crack and carries the tensile forces over the crack, thereby creating a post-breakage load-carrying mechanism. Various parameters that may influence the structural performance of the reinforced glass beams are experimentally investigated in this dissertation, namely: bond system, temperature, thermal cycling, humidity, load duration, reinforcement material, reinforcement percentage and beam size. This is done by means of pull-out tests, to investigate the pull-out strength of the reinforcement, and by means of bending tests, to investigate the structural response of the reinforced glass beams. Furthermore, analytical and numerical investigations are performed into the modelling of the structural response of reinforced glass beams. The analytical model has been developed in this research in analogy with reinforced concrete. The numerical model makes use of a novel sequentially linear analyses (SLA) scheme and saw-tooth reduction diagrams to simulate cracking of the glass and yielding of the reinforcement and to describe the overall structural response of the beams.Building TechnologyArchitectur
Safety Concepts in Structural Glass Engineering: Towards an Integrated Approach
No full textThis dissertation proposes the Integrated Approach to Structural Glass Safety, based on four clearly defined element safety properties, damage sensitivity, relative resistance, redundancy, and fracture mode. The Element Safety Diagram (ESD) is introduced to provide an easy-to-read graphical representation of these properties. The safety performance of a large number of glass beam designs has been compared through experimental testing based on the proposed approach. The effects of a wide range of safety enhancing design measures on each element safety property is extensively discussed. Elastic strain energy release is identified as a, hitherto underexposed, parameter with major influence on redundancy – the most important safety property. Finally, the Integrated Approach is applied to re-evaluate the safety of two full-scale case-study projects which started this study.Building TechnologyArchitectur
Modelling of settlement induced building damage
No full textThis thesis focuses on the modelling of settlement induced damage to masonry buildings. In densely populated areas, the need for new space is nowadays producing a rapid increment of underground excavations. Due to the construction of new metro lines, tunnelling activity in urban areas is growing. One of the consequences is a greater attention to the risk of damage on existing structures. Thus, the assessment of potential damage of surface buildings has become an essential stage in the excavation projects in urban areas (Chapter 1). The current damage risk assessment procedure is based on strong simplifications, which not always lead to conservative results. Object of this thesis is the development of an improved damage classification system, which takes into account the parameters influencing the structural response to settlement, like the non-linear behaviour of masonry and the soil-structure interaction. The methodology used in this research is based on experimental and numerical modelling. The design and execution of an experimental benchmark test representative of the problem allows to identify the principal factors and mechanisms involved. The numerical simulations enable to generalize the results to a broader range of physical scenarios. The methodological choice is based on a critical review of the currently available procedures for the assessment of settlement-induced building damage (Chapter 2). A new experimental test on a 1/10th masonry façade with a rubber base interface is specifically designed to investigate the effect of soil-structure interaction on the tunnelling-induced damage (Chapter 3). The experimental results are used to validate a 2D semi-coupled finite element model for the simulation of the structural response (Chapter 4). The numerical approach, which includes a continuum cracking model for the masonry and a non-linear interface to simulate the soil-structure interaction, is then used to perform a sensitivity study on the effect of openings, material properties, initial damage, initial conditions, normal and shear behaviour of the base interface and applied settlement profile (Chapter 5). The results assess quantitatively the major role played by the normal stiffness of the soil-structure interaction and by the material parameters defining the quasi-brittle masonry behaviour. The limitation of the 2D modelling approach in simulating the progressive 3D displacement field induced by the excavation and the consequent torsional response of the building are overcome by the development of a 3D coupled model of building, foundation, soil and tunnel (Chapter 6). Following the same method applied to the 2D semi-coupled approach, the 3D model is validated through comparison with the monitoring data of a literature case study. The model is then used to carry out a series of parametric analyses on geometrical factors: the aspect ratio of horizontal building dimensions with respect to the tunnel axis direction, the presence of adjacent structures and the position and alignment of the building with respect to the excavation (Chapter 7). The results show the governing effect of the 3D building response, proving the relevance of 3D modelling. Finally, the results from the 2D and 3D parametric analyses are used to set the framework of an overall damage model which correlates the analysed structural features with the risk for the building of being damaged by a certain settlement (Chapter 8). This research therefore provides an increased experimental and numerical understanding of the building response to excavation-induced settlements, and sets the basis for an operational tool for the risk assessment of structural damage (Chapter 9).Structural EngineeringCivil Engineering and Geoscience
Comparison of Solid, Shell and Plane stress models for simulating Masonry wall-piers systems
No full textCivil Engineering and GeosciencesStructural Engineerin
Structural damage in masonry: Developing diagnostic decision support
No full textThis thesis deals with the diagnosis of structural damage in traditional masonry: cracks, deformations and tilts. Establishing the cause of this type of damage can be difficult. This research project has aimed to improve and facilitate the diagnostic process by offering support in the initial phase in which hypotheses are generated. The more precise hypotheses are formulated, and the more accurate they are classified, the more effective the further process of verification will be and the greater the probability that the final diagnosis is correct. This study has specifically focused on characteristics that can be assessed in a first survey, either visually or with the help of some simple tools or archive material. With questionnaires, a literature review of over 500 cases of damage and numerical and small-scale physical tests, the relations between symptoms of damage, their causes and their contexts (in terms of material, geometry, environment and time) have been investigated. This has resulted in a diagnostic decision support tool that helps surveyors to distinguish between causes by offering support in interpreting structural damage in masonry. The results of a user test, in which potential users applied our tool to damage cases from their practice, are positive: our tool was generally considered to be very instructive. The main contribution of this study lies in improving knowledge exchange. The existing, but highly fragmented and often seemingly contradictory information has been combined, structured and assessed on its value for diagnosing structural damage in masonry. With this thesis and the accompanying tool (ISBN 978-90-8570-760-8), expert knowledge is now made accessible to a wider group of people. Supplemental material published as: Prototype of a diagnostic decision support tool for structural damage in masonry ISBN 978-90-8570-760-8 Under: http://resolver.tudelft.nl/uuid:e9a3a2f9-16b5-4b22-a1f4-6511f3543f6eBuilding TechnologyArchitectur
Prototype of a diagnostic decision support tool for structural damage in masonry
No full textThis prototype of a diagnostic decision support tool for structural damage in traditional masonry is the result of a PhD research project. The research project has aimed to improve and facilitate the diagnostic process by offering support in the initial phase in which hypotheses are generated. The more precise hypotheses are formulated, and the more accurate they are classified, the more effective the further process of verification will be and the greater the probability that the final diagnosis is correct. Based on an extensive literature review of over 500 cases of structural damage, 60 characteristic damage patterns have been identified. For each of these damage patterns, possible causes have been listed. Essential context conditions (in terms of material, geometry, environment and time) allow one to discriminate between these hypotheses. A decision tree helps users determine which of the 60 damage patterns most closely matches the damage they are investigating. All further information on hypotheses and conditions is provided tailored to the selected pattern. For settlement-related damage processes, a separate part gives more details on underlying causes and essential conditions. For more background information on the development of this tool and on the terms used in it, the reader is referred to the PhD thesis ‘Structural damage in masonry: Developing diagnostic decision support’ (ISBN: 978-90-8570-759-2). Under: http://resolver.tudelft.nl/uuid:ced08aa2-c2e8-4aa8-9559-870bf12d5ba5Building TechnologyArchitectur
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