Structural response of timber-concrete composite slabs: Effect of shear fasteners with different spacings and orientations.

Abstract

This thesis investigates the structural response of timber-concrete composite (TCC) slabs, with a specific focus on the influence of shear fasteners. The primary objective is to investigate the load capacity of TCC with shear fasteners that are of different orientations and spacings.

The connection plays an important role in the degree of efficiency of the composite structure and the function of a corresponding floor structure. Shear connection refers to all the possible methods to connect timber and concrete and has a critical impact on the function of TCC structure. Shear fasteners are the most common connection system. It is a type of metal connector in the form of screws, bolts and nails.

The TCC investigated in this thesis is CLT-concrete slabs connected with CTC screws. CTC is a connector for timber-concrete floor which are self-drilling and easy to install. Several research articles have highlighted that the use of screws oriented at 45° angle results in higher stiffness and load capacity values. Similarly, the feedback from applying CTC screws at a 45° inclination supports this.

This thesis considered screws installed at a single 90° and 45° crossed orientation. The challenge is that the research on screws with 90° is limited. Therefore, two types of orientations, along with different spacings are investigated in this thesis. 15 specimens are used with 5 different groups, and each group has 3 identical specimens. 3 groups with 90° and 2 groups with 45°. One group from both 45° and 90° had the same number of screws to see the comparison between them. With the main goal being the reduction of time and effort in the installation of the system using 90°. Also, to see if the manufacturing process could be automated.

The theoretical calculation predictions are performed by using the γ-method and shear analogy method to find the maximum load applied and maximum deflection both for the short-term and long-term. All theoretical predictions were performed before the laboratory tests and the values from the maximum load applied were used to perform the four-point bending test. The long-term maximum load applied was the value used for the test setup.

The laboratory test was then compared to the theoretical predictions to discuss the results. In general, the specimens with screws installed at 45° inclination had a higher load capacity. They also had a capacity that was higher than the short-term predictions and the same as the long-term predictions. 90° on the other hand underperformed and had results that could be compared to the short-term predictions. One of the groups for 90° screws showed results for the maximum load applied that were close to 45°. In the lateral displacement 90° showed that the slip between the concrete and timber was much greater.

This thesis investigates the structural response of timber-concrete composite (TCC) slabs, with a specific focus on the influence of shear fasteners. The primary objective is to investigate the load capacity of TCC with shear fasteners that are of different orientations and spacings.

The connection plays an important role in the degree of efficiency of the composite structure and the function of a corresponding floor structure. Shear connection refers to all the possible methods to connect timber and concrete and has a critical impact on the function of TCC structure. Shear fasteners are the most common connection system. It is a type of metal connector in the form of screws, bolts and nails.

The TCC investigated in this thesis is CLT-concrete slabs connected with CTC screws. CTC is a connector for timber-concrete floor which are self-drilling and easy to install. Several research articles have highlighted that the use of screws oriented at 45° angle results in higher stiffness and load capacity values. Similarly, the feedback from applying CTC screws at a 45° inclination supports this.

This thesis considered screws installed at a single 90° and 45° crossed orientation. The challenge is that the research on screws with 90° is limited. Therefore, two types of orientations, along with different spacings are investigated in this thesis. 15 specimens are used with 5 different groups, and each group has 3 identical specimens. 3 groups with 90° and 2 groups with 45°. One group from both 45° and 90° had the same number of screws to see the comparison between them. With the main goal being the reduction of time and effort in the installation of the system using 90°. Also, to see if the manufacturing process could be automated.

The theoretical calculation predictions are performed by using the γ-method and shear analogy method to find the maximum load applied and maximum deflection both for the short-term and long-term. All theoretical predictions were performed before the laboratory tests and the values from the maximum load applied were used to perform the four-point bending test. The long-term maximum load applied was the value used for the test setup.

The laboratory test was then compared to the theoretical predictions to discuss the results. In general, the specimens with screws installed at 45° inclination had a higher load capacity. They also had a capacity that was higher than the short-term predictions and the same as the long-term predictions. 90° on the other hand underperformed and had results that could be compared to the short-term predictions. One of the groups for 90° screws showed results for the maximum load applied that were close to 45°. In the lateral displacement 90° showed that the slip between the concrete and timber was much greater.