Long-term behaviour of Timber Concrete Composite elements - Finite element study of long-term deflections caused by creep and shrinkage
Typ
Examensarbete för masterexamen
Program
Sound and vibration (MPSOV), MSc
Publicerad
2022
Författare
Wiik, Samuel
Käll, Carl-Johan
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
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.
Beskrivning
Ämne/nyckelord
TCC, long-term, deflection, shrinkage, creep, FE-modelling