Diaphragm action in modern medium-rise timber/hybrid structures A finite element parametric study of diaphragm response in modern timber/hybrid structures

Examensarbete för masterexamen
Master's Thesis
Structural engineering and building technology (MPSEB), MSc
Thornadtsson, Emil
In the design of the structural system of a structure, the knowledge of how the diaphragm distributes the horizontal actions is of essential importance. A diaphragm can be classified as, rigid, semi-rigid, or flexural, where the classification is governed by the structural response of the diaphragm. Furthermore, a rigid diaphragm is characterized by a stiffness distribution of horizontal actions to the later load- resisting structures, a flexible diaphragm is characterized by the horizontal actions distributed by tributary area to the later load-resisting structures, and the semi- rigid classification is characterized by the diaphragm response is a combination of the rigid and flexural response. The classification of the diaphragm, however, is not intuitive in timber structures as there is a variety of variables that influence the response of a timber diaphragm, e.g, of timber products, timber connections, etc., and the guidance provided by today’s building regulations is insufficient. Furthermore, guidance in literature is often in unquantified terms such as - the diaphragm can be considered rigid if the diaphragm is a lot stiffer than the shear walls, and vice versa for a flexural response. Hence, this project’s aim is to determine stiffness relation boundaries for a variety of commonly used timber/TCC diaphragm types, where the influence of stiffness variations of the structural joints of adjoining element/panels are taken into respect, and the LLRS, that quantifies if the diaphragm response is flexible, semi-rigid or rigid. To obtain the aim was a finite element parametric study executed, examining the diaphragm response under extensive stiffness variations of the later load-resisting structures. The parametric study was performed in the software FEM-Design, by a coded C-sharp script that looped analysis with stiffness increment of the LLRS or the structural joint o a diaphragm. Obtained results from the parametric study showed that the stiffness of structural joints in timber diaphragm has a great impact on the overall response and cannot be neglected in diaphragm analysis. Stiffness relations of the diaphragms and LLRS to classify the diaphragm response were obtained for the structural floor plan of Object 1, however, for the structural floor plan of Object 2 were no correlations of stiffness relations found. Finally, the obtained stiffness relations of the structural floor plan of Object 1 need further studies to be confirmed.
diaphragm, diaphragm action, in-plane stiffness, parametric stiffness study, stabilization, horizontal load distribution.
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