02 Décembre – Thesis defense - Minh Van Thai
15 h Room 101 - Building A29 / University of Bordeaux (Talence campus)
Evaluation of the vibration behavior and optimization of the conception of CLT-concrete floors.
This research project aims to evaluate the vibration behavior and optimize the design of cross-laminated timber-concrete composite floors. These floor structures are a composite made of a cross-laminated timber panel and a concrete layer. They are connected by a notch carved into the cross-laminated timber and reinforced by two vertical screws. This connection is an innovative solution and still needs further regulation by a technical notice. Nonetheless, it remains economically accessible, requires only simple machining, and limits on-site intervention. The composite floor will have a large span necessary, particularly in Quebec and France, to construct multi-story timber buildings whose market is in development. Such floor systems will satisfy the demand for low or no carbon footprint floor solutions for reducing the static height while complying with the normative constraints of which the most demanding is the vibration. First, the behavior of a single composite notch connector was studied. The screw reinforced notched connector has been tested in static shear. Finite element model has been proposed to describe the static stiffness and the shear strength of the connector of different configurations. Then, three long-span (9 meters) cross-glued laminated timber-concrete beams with different connector densities were subjected to vibration and static bending tests. Analytical expressions proposed by Eurocode 5 and a simplified finite element model gave reasonable estimates of the measured natural frequencies. However, a module calibration of the cross-laminated timber panels due to the impact of the notches was necessary. Finally, multi-objective optimization of cross-laminated timber-concrete floors was carried out. Its objectives were to minimize the weight, the static height of the floor, and the total cost while complying with the constraints of the serviceability limit state (deflection and vibration) and the ultimate limit state (bending and shearing). A Pareto front of optimized solutions was obtained. The configuration tested is a conventional engineering solution that does not appear on this Pareto front. The optimization tool is, therefore, potentially relevant and can help engineers define their designs.