| 1. |
- Adiels, Emil, 1989, et al.
(författare)
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The use of virtual work for the formfinding of fabric, shell and gridshell structures
- 2018
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Ingår i: Proceedings of the Advances in Architectural Geometry conference 2018. - 9783903015135 ; , s. 286-315
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Konferensbidrag (refereegranskat)abstract
- The use of the virtual work theorem enables one to derive the equations of static equilibrium of fabric, shell and gridshell structures from the compatibility equations linking the rate of deformation of a surface to variations in its velocity. If the structure is treated as a continuum there is no need to consider its micro-structure provided that the grid is fine compared to the overall geometry. Thus we can include fabrics, ribbed shells, corrugated shells and gridshells with a fine grid, such as the Mannheim Multihalle. The equilibrium equations are almost identical to those obtained by assuming that a shell is thin and of uniform thickness, but are more general in their application. Our formulation introduces the concept of geodesic bending moments which are relevant to gridshell structures with continuous laths. The virtual work theorem is more general than the energy theorems, which it in- cludes as a special case. Hence it can be applied to surfaces which admit some form of potential, including minimal surfaces and hanging fabrics. We can then use the calculus of variations for the minimization of a surface integral to define the form of a structure. Many existing formfinding techniques can be rewritten in this way, but we concen- trate on surfaces which minimize the surface integral of the mean curvature subject to a constraint on the enclosed volume, producing a surface of constant Gaussian curvature. This naturally leads to the more general study of conjugate stress and curvature directions, and hence to quadrilateral mesh gridshells with flat cladding panels and no bending moments in the structural members under own weight.
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| 2. |
- Larsson, Jenny, et al.
(författare)
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Moving Mesh and Image Registration in FEniCS
- 2017
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Ingår i: Proceedings of 30th Nordic Seminar on Computational Mechanics – NSCM30. - : Technical University of Denmark. ; , s. 180-183
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Image registration is about finding a transformation that warps a source image into a target image, matching gross features. It is a critical task in medical imaging. Computational anatomy (CA) is a state-of-the-art framework for image registration, founded in the theory of fluid dynamics and PDE: one seeks a time-dependent vector field that generates a continuous warp of the source image into the target image.Here we construct a finite element realisation of CA by representing the continuous warp by a moving mesh. The PDE governing the motion of the mesh is an infinitedimensional nonlinear gradient flow; a brief description is given in section 2. In essence, it is a time-stepping problem, where an elliptic PDE is solved in each time step using the FEniCS finite element package. The solution process is summarised in fig. 1.Although commonly used in medical contexts, we stress that CA has promising applications also in structural engineering, as discussed in section 4.
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| 3. |
- Miki, Masaaki, et al.
(författare)
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Form-finding of shells containing both tension and compression using the Airy stress function
- 2022
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Ingår i: International Journal of Space Structures. - : SAGE Publications. - 0956-0599 .- 2059-8033. ; 37:4, s. 261-282
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Tidskriftsartikel (refereegranskat)abstract
- Pure-compression shells have been the central topic in the form-finding of shells. This study investigated tension-compression mixed-type shells by utilizing a NURBS-based isogeometric form-finding approach that analyses Airy stress functions to expand the possible plan geometry. A complete set of smooth version graphic statics tools is provided to support the analyses. The method is validated using examples with known solutions, and a further example demonstrates the possible forms of shells that the proposed method permits. Additionally, a guideline to configure a proper set of boundary conditions is presented through the lens of asymptotic lines of the stress functions.
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| 4. |
- Sehlström, Alexander, 1987, et al.
(författare)
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Architectural design methods used in engineering Master's thesis projects
- 2021
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- By letting structural engineering thesis students explore questions using architectural design methods, they creatively and systematically addressed holistic questions while maintaining a technical depth. The approach may serve as a model to increase engineering students' ability to insightfully contribute to solutions for complex societal problems.
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| 5. |
- Sehlström, Alexander, 1987, et al.
(författare)
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Design of tension structures and shells using the Airy stress function
- 2022
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Ingår i: International Journal of Space Structures. - : SAGE Publications. - 0956-0599 .- 2059-8033. ; 37:2, s. 94-106
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Tidskriftsartikel (refereegranskat)abstract
- Discontinuities in the Airy stress function for in-plane stress analysis represent forces and moments in connected one-dimensional elements. We expand this representation to curved membrane-action structures, such as shells and cable nets, and graphically visualise the internal stresses and section forces at the boundary necessary for equilibrium. The approach enhances understanding of the interplay between form and forces and can support design decisions related to form-finding and force efficiency. As illustrative examples, the prestressing needed for three existing cable nets is determined, and its influence on the edge-beam bending moment is explored.
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| 6. |
- Sehlström, Alexander, 1987
(författare)
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Förspända träkonstruktioner
- 2019
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Ingår i: Bygg & Teknik. - 0281-658X.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Sehlström, Alexander, 1987, et al.
(författare)
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On multi-objective topology optimization and tracing of Pareto-optimal structures
- 2016
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper an sequential linear programming (SLP) algorithm for solving multi-objective topology optimization problems have been implemented and numerical results for a design domain have been calculated. Examples shows that the SLP algorithm performs similar to the single objective ptimality criteria algorithm but also that some further work is needed.
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| 8. |
- Sehlström, Alexander, 1987, et al.
(författare)
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Pre-stressed Geodesic Gridshell
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Timber gridshells can cover large spaces with minimum material. However, with long-term creep deformations, small cross sections and high elasticity, there are potential stability issues. Historically, pre-stressing systems have been shown to prevent instability modes in unstable structures. In this project we investigate the benefits of pre-stressing a geodesic elastic bending-active gridshells serving as a lecture pavilion. Digital analysis and physical tests are interactively combined to study and implement various modelling and analysis techniques, pre-stress configurations and connection details. It is found that an internal pre-stressing system can significantly increase the stability of in terms of eigenfrequencies.
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| 9. |
- Sehlström, Alexander, 1987
(författare)
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Prestress and its application to shell, fabric, and cable net structures
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Prestressing and shells provide means to create material-efficient and well-functioning structures, as do their combination, offering opportunities for increased material efficiency within the built environment. Prestressing introduces stresses in an object to enhance its performance, and shells include concrete shells, masonry vaults, fabric structures, cable nets, and timber or steel gridshells. Both prestressing and shell structures come with technical and practical considerations that need attention during the design, or there is a risk of wasted opportunity. However, successful attention to and combination of these aspects, resulting in a material-efficient prestressed shell, is not enough to make a high-quality architecture. There is a need for additional project-specific considerations, requiring ways to study design choices' impact on structural and architectural aspects. This thesis aims for an increased understanding of prestressing and its application to shell, fabric, and cable net structures and improved means for their design. It provides a broad overview of prestressing, expanding beyond the common perception of prestress being limited to concrete structures, and shell structures, focusing on applications within architecture. The scope is the combination of prestressing and shells, and it addresses three main research questions: (1) Can any shell be prestressed? For those that can, what is the meaning and influence of prestressing?; (2) How can prestressed shells be form-found using analytical and numerical approaches?; and (3) How can prestress in shells be represented and chosen, aspiring for efficient structural performance? Appended papers A-F help answer these questions, and the thesis contributes to architectural and structural design and structural optimisation and applies differential geometry. It provides approaches for the form-finding of gridshells containing both tension and compression elements (Paper A) and of minimal surfaces (Paper C and D). Paper B concludes that a sphere cannot be prestressed, but a torus can. Paper E extends the Williams and McRobie (2016) discontinuous Airy stress function from flat structures to curved shells, allowing moments and shear forces in edge beams of shell structures to be quantified and appropriate prestressing chosen. Paper D uses a discrete Airy stress function and discusses the structural behaviour of shells with negative Gaussian curvature loaded with patch loads. Paper D studies Eduardo Torroja's prestressed concrete Alloz aqueduct, concluding that longitudinal prestressing may reduce the wall bending moments and that, at the limit, the channel act as a cylindrical membrane-action shell rather than of an Euler-Bernoulli beam, enabling thinner cross-sections.
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| 10. |
- Sehlström, Alexander, 1987
(författare)
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Prestress in Nature and Technics
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To direct the forces of nature is a central task in the creation of spaces and load-carrying structures for architecture. This research investigates how prestress can be used as a design tool for the creation of material efficient and well-functioning structures, and in early design stages contribute to sustainable, functional and beautiful architecture. The thesis begins with a discussion about central concepts such as stress and stiffness. Stiffness can be understood as the sum of elastic stiffness and geometric stiffness and the latter is differently influenced by the presence of tensile or compressive stresses. Only structures that are statically indeterminate are possible to prestress so that the stress pattern is affected. The terms externally-equilibrated and auto-equilibrated prestressed structures are introduced. The design of load-bearing structures for architecture requires a collaboration between architects and engineers and the conditions for a successful collaboration is reflected upon. Prominent design cultures are highlighted and the one this research is linked to is described. A collection of historic and contemporary examples of prestressed structures is presented. The focus is architectural applications but examples from other realms are also included. From this collection, a framework for prestressed structures is proposed and discussed which considers five perspectives. The first explores the historical knowledge development. The second is devoted to structural mechanical modes of actions where material behaviour, member actions and structural systems are discussed. The third highlights computational strategies and those appropriate for early stage design are distinguished from those suitable for late stage verification. The fourth perspective seeks to establish objectives for why prestress is used. The fifth perspective leads to suggestions for strategies for how the prestress is achieved. Three papers are included. Paper A presents a numerical method for the form finding of prestressed gridshells consisting of both compressed and tensioned members. Paper B describes a structural design process where methods usually applied by architects are used by structural engineers. The work resulted in the construction of a temporary pavilion consisting of a post-tensioned wooden gridshell called the Wood Fusion Pavilion. Paper C explores under what conditions an unloaded shell formed of a closed surface unattached to any supports can contain a state of membrane stress which can be induced by prestressing. It is concluded that a torus can be prestressed, but there must almost certainly be more to explore.
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