In-Plane Experimental Testing of Timber-Concrete Composite Floor Diaphragms

Recent advances in multistory timber building design have led to new structural systems that allow open floor plans with large spans between frames and/or walls. Timber-concrete composite (TCC) flooring can achieve the spans required but has the potential to be flexible under diaphragm actions, which can significantly alter the seismic response of a building. In-plane experimental tests on a 3 m by 3 m one-third scale TCC floor were performed using quasi-static earthquake loading simulation. The experimental results indicate that the deformation between the floor and lateral load resisting systems (LLRS) is much greater than the in-plane deformation of the floor diaphragm. Hence, a floor system with similar aspect ratio can be modeled as a single-degree-of-freedom for future structural analyses. Different connections were considered between the floor unit and lateral restraints, which simulate the LLRS. The connection was either timber-to-timber or concrete-to-timber and incorporated screws or nails acting as dowels or inclined at 45°. Each connection type performed differently in terms of stiffness, strength, ductility capacity, and induced damage. Screws that were oriented at 45° to the connection interface were significantly stiffer than fasteners aligned orthogonal to the interface. There was little difference in the initial stiffness for the concrete-to-timber connection compared to the timber-to-timber connection. The testing indicated that a timber-to-timber interface is more desirable because of construction ease and reparability. The in-plane response of the floor system is modeled using finite elements and compared to experimental results. Design recommendations are provided for the cyclic strength of inclined wood fasteners.