Disputation i byggteknik: Le Kuai

Zoom-länk för disputationen: https://lnu-se.zoom.us/j/5645444933?pwd=ZmxYR3lSdWwzditOYWxtV2lTYXlCZz09

Abstract     

Wood is a sustainable material from nature that has a longstanding tradition as a building material. Compared to other construction materials, such as steel and concrete, the significance of using structural timber and engineered wood products has increased in recent years because they are regarded as a renewable source and require a low carbon footprint and less energy consumption during production. In Scandinavia, the European design standard EN 1995-1-1 (EC5) is extensively used to guide structural engineers in the design of timber structures, while addressing safety and serviceability issues. However, this standard relies on multiple simplifications to achieve simple semiempirical hand calculations. In addition to these simplified expressions, engineers and researchers need reliable numerical models to study the racking behaviour of light-frame timber structures with arbitrary geometry under complex loading conditions. Such modelling tools must be computationally effective, easy to use and able to simulate the global structural behaviour as well as the local fastener force distributions and the crack growth in the sheathing panels.

   The main aim of this doctoral thesis is to develop a numerical model to analyse the complex structural behaviour of prefabricated light-frame timber modules. The model is developed in the commercial finite element software ABAQUS^® with the assistance of the parametric Python scripting method. This thesis work also includes development of a graphical user interface in Python for user-friendly inputs, outputs, and visualisation of the numerical results. The simulation tool was used to study two different structural applications, firstly light-frame timber walls and then light-frame timber modules.

   For these applications, the modelling of the mechanical sheathing-to-framing joints is very important. In the first paper application, oriented and uncoupled elastic spring-based connectors were used to simulate the sheathing-to-framing joints. To define the material parameters for the connector, new Eurocode-based expressions were also presented. To simulate the permanent displacements in the sheathing-to-framing joints a coupled elasto-plastic spring-based connector model was proposed in papers II and III for both isotropic and orthotropic joint properties.

   To validate the accuracy of the numerical model, full-scale experimental tests were conducted for light-frame timber walls and modules. The validation indicates that by using effective 3D structural elements, the model achieves a satisfying balance between computational efficiency and reasonable accuracy. The numerical results presented for the applications agreed well with experimental results, regarding the global and local displacements and crack growth in the sheathing panels. The simulation results also increased the understanding of local joint behaviour in terms of fastener forces and their directions.

      The developed model was used to perform numerous parametric studies and thus investigate how different geometries, sheathing panels, connection types or boundary conditions affect the global and local structural behaviour of light-frame timber structures. These studies demonstrate how the parametric modelling can easily be used to analyse how different parameters have influence on these types of structures and significantly reduce the number of experimental tests necessary to perform.

     The parametric model has also the potential to be further developed for the structural design of more complex modular-based multi-storey timber buildings. Furthermore, the proposed orthotropic elasto-plastic spring-based connector model can be further calibrated to simulate the performance of dowel-type connections in wood-based materials.

Keywords: Light-frame timber wall and module, FE-modelling, Parametric modelling, Elasto-plastic connector model, Full-scale experimental test