Long-term behaviour of Timber Concrete Composite elements - Finite element study of long-term deflections caused by creep and shrinkage
Examensarbete för masterexamen
Sound and vibration (MPSOV), MSc
Timber Concrete Composite (TCC) is a hybrid structure for effective material uti lization, combining the compression performance of concrete with the tension ca pacity of timber. There are multiple design possibilities in terms of cross-sectional design, production method and type of connection. Especially the latter has a signif icant impact on the behaviour. Additionally, the interaction of timber and concrete causes a complex long-term behaviour, with deflections often being a critical aspect. The design approach presented in Eurocode 5 is based on an analytical calculation method called the γ-method (“gamma”-method). There, an effective cross-sectional stiffness is calculated based on the interaction degree between the timber and con crete. The γ-method has several limitations in terms of applicability and accuracy, and a more conformable solution procedure is achieved with a numerical analysis. In this work, the Finite Element software Abaqus is used as a numerical solver, where a modelling procedure for a “T”-cross-section is established. It is then used in a two-part parametric study to evaluate the long-term deflections of TCC elements. In the first part of the parametric study, the impact of shrinkage and creep is evaluated for a chosen cross-section. The concrete shrinkage has a significant impact on the deflections, especially for high-stiffness connections. However, if the timber shrinks as well, the deflection increase is counteracted. The creep of timber and connection has a large impact on the estimated deflections. Contrary, the concrete creep factor has a much smaller influence for the studied cross-section. The second part of the parametric study investigate the concrete shrinkage impact together with cross-sectional design optimisations. In the studied case, increasing the concrete thickness is inefficient since the long-term load case is highly dependent on the self weight, and the additional concrete weight counteracts the stiffness increase. The conclusions of the study is that concrete shrinkage has a potentially large im pact on the deflections, however the γ-method neglects its impact. Prefabrication of the concrete or using low-shrinkage concrete are suggested measures to reduce the deflection caused by its shrinkage. Additionally, further studies of lightweight concrete is suggested to reduce the dominant load-impact of the self-weight.
TCC, long-term, deflection, shrinkage, creep, FE-modelling