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- Larsson, Gustaf
(författare)
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High capacity timber joints : Proposal of the shear plate dowel joint
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An increased use of wood can reduce the environmental footprint of the building sector by being a renewable and ecological material. In order to improve the competitiveness of heavy timber structures, this thesis presents a novel type of timber connection with a high degree of prefabrication, which utilizes a resilient bond line.It has previously been shown that a large conventional stiff adhesive bond line acting in shear can be made stronger by using a less stiff bond line, by e.g. introducing an intermediate rubber foil. The scientific contribution of this thesis starts by comparing such resilient bond lines to conventional non-resilient bond lines. It is numerically shown that the strength of the bond line is increased from 40% to 80% of the local shear strength by introducing a resilient bond line in large lap joints. Unlike other types of connections, a resilient bond line enables design of the stiffness depending on the application by varying the hardness and thickness of the intermediate bond layer.Using the concept of the resilient bond line in a heavy timber connection design aiming for a high degree of prefabrication, the novel Shear Plate Dowel Joint (SPDJ) is proposed. Initially designed for truss nodes, the connection shows promising results in full scale tensile tests with an average shear stress at failure of 3.3 MPa. A bond line model to be used in FE analysis of the SPDJ is proposed and used in parameter studies of the connection. It is found that a softer bond line will increase the slip, but also the strength which asymptotically aligns with theory of perfect plasticity.The strengths of the SPDJ design are high load carrying capacity and simplicity in design, but duration of load effects and fire resistance are, among other things, in need of further research prior to structural application.
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- Andersson, Linus
(författare)
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Reduced order modeling in structural dynamics : Consideration of local nonlinearities
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A structural design process may include various load cases for which a sufficient load-bearing capacity must be demonstrated. In addition to static load cases, a verification of dynamic loads, e.g. accidental loads such as blast and impact loading, may be required. To this end, the response may be estimated using a computational model representing an idealized structure. Particularly in the conceptual design phase, a time-efficient and straightforward modelingapproach can be of great utility, allowing for an interactive design process where alternative designs may be tested. Furthermore, a dynamic response analysis often requires some form of time (or frequency) discretization and can therefore become computationally expensive compared to the corresponding static analysis. The balance between performance and accuracy as well as the purpose, i.e. the output quantities of interest, are thus important aspects in a dynamic response analysis.A structural dynamics analysis typically requires a model being accurate as well as computationally efficient. The model accuracy is particularly important in a verification of structurescharacterized by brittle failure modes, i.e. that do not deform plastically before failure. Furthermore,to avoid a too conservative design and to ensure sufficient accuracy, it can be necessary to consider the nonlinear response of a structure, e.g. due to contact interactions or nonlinear material behavior. However, a nonlinear structural dynamic problem often requires computationallyexpensive solution methods. Consequently, there is a need for modeling strategies that enable time-efficient, accurate analyses and a straightforward modeling approach, appropriate in a structural design process. To achieve this, a reduced order model can be established providing an accurate prediction of important output quantities.Dynamic substructuring turns out to be an important aspect in the process of developing reduced order models. By subdivision of the structure into substructures, dynamic substructuring can be employed to effectively adjust the level of accuracy for different parts of the structure. For example, substructures that remain linear elastic can typically be modeled using mode-superposition methods whereas substructures which exhibit a nonlinear behavior can berepresented by a refined submodel.In the dissertation, strategies for reduced order modeling are investigated on the basis of structural engineering applications within two different areas, namely concrete structures subjected to blast loading and glass structures subjected to soft-body impact. Interestingly, however, some of the challenges with regard to the structural dynamics problems are similar. In particular, the response of higher order modes may be of importance and, moreover, an accuraterepresentation of the structural behavior may necessitate a model considering local nonlinearities.By means of dynamic substructuring, computationally efficient analysis techniques are developed for evaluating concrete structures subjected to blast loading, appropriate for use in a structural design process. In particular, a comparison to commonly used modeling strategies, using equivalent single-degree-of-freedom systems, suggests that the developed models providean increased accuracy of the shear force. Brittle failure modes such as shear failure are typically critical for concrete structures subjected to blast loading.Furthermore, reduced order models are established for verification of glass panels subjected to soft-body impact. In particular, a non-linear viscous single-degree-of-freedom system is proposed for reduced modeling of the standardized EN 12600 impactor. Further, the response of higher order modes is considered using a set of load-dependent mode shapes. The developed models are validated by experimental tests of impact on glass panels.Finally, a review of various reduced order modeling techniques is presented which, in a broader perspective, provide a basis for developing reduced order models in various structural engineering applications.
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