Testing of CLT-Concrete Composite decks

Abstract: When massive timber decks are used in buildings the design is often regulated by serviceability limit state (SLS), mainly the vibration criteria. To decrease the risk for vibrations of a deck the bending stiffness needs to be increased. To increase the bending stiffness of the deck either the depth of the deck can be increased or the stiffness of the used material. The most common way to increase the bending stiffness is to increase the depth of the deck. In this thesis it was tested if a composite deck could be used. Composite decks consisting of timber and concrete are often referred to as TCC meaning Timber-concrete composite. TCC can be an alternative by combining the two above mentioned methods of increasing the bending stiffness. By creating a TCC deck by adding and connecting a concrete slab to the upper-side of the timber deck the bending stiffness can be increased while keeping the depth of the deck to a minimum. To make TCC a possible alternative to be used in modern buildings it is necessary to be able to accurately predict necessary quantities such as the load-bearing capacity and bending stiffness. In this report the main objective is to investigate how well an existing calculation method, the gamma-method, can predict the bending stiffness and therefore the deflections. To reach the aim of the report tests are performed on the TCC's and the connections that are used. Shear tests are performed on the connections in order to determine their stiffness. Bending tests are performed on four TCC-decks, two of which are tested to failure. The bending stiffness of the TCC is dependent on the stiffness of the connection between the different parts of the cross-section. Two types of connections to connect the concrete slab to the wooden deck were investigated. The first type is a connection through notches cut in the wooden deck and the second is by applying an epoxy adhesive to the wooden deck prior to casting the concrete. The experimental test results showed that the prediction of the mid-span deflections with the gamma-method could be accurate. The level of accuracy could not be determined due to that it is dependent on several parameters such as the stiffness of the timber and concrete as well as the stiffness of the connections used, of which the concrete's compressive stiffness was not tested. The test results also showed the difficulty to accurately determine the stiffness of the connection by performing shear tests. One part of the experimental study was to check the bearing capacity of two of the TCC-decks by performing a destructive bending test. The results from the destructive bending test revealed that a high load-bearing capacity can be expected from a TCC.