The rise of wood buildings in the skylines of cities forces structural dynamic and timber experts to team up to solve one of the new civil-engineering challenges, namely comfort at the higher levels, in light weight buildings, with respect to wind-induced vibrations. Large laminated timber structures with mechanical joints are exposed to turbulent horizontal excitation with most of the wind energy blowing around the lowest resonance frequencies of 50 to 150 m tall buildings. Good knowledge of the spatial distribution of mass, stiffness and damping is needed to predict and mitigate the sway in lighter, flexible buildings. This paper presents vibration tests and reductions of a detailed FE-model of a truss with dowel-type connections leading to models that will be useful for structural engineers. The models also enable further investigations about the parameters of the slotted-in steel plates and dowels connections governing the dynamical response of timber trusses.
This thesis focuses on the structural performance of mass timber panel-concrete composite floors with notches. Mass timber panels (MTPs) such as cross-laminated timber, glue-laminated timber, and nail-laminated timber, are emerging construction materials in the building industry due to their high strength, great dimensional stability, and prefabrication. The combination of MTPs and concrete in the floor system offers many structural, economic, and ecological benefits. The structural performance of MTP-concrete composite floors is governed by the shear connection system between timber and concrete. The notched connections made by cutting grooves on timber and filling them with concrete are considered as a structurally efficient and cost-saving connecting solution for resisting shear forces and restricting relative slips between timber and concrete. However, the notched connection design in the composite floors is not standardized and the existing design guidelines are inadequate for MTP-concrete composite floors.
To study the structural performance of notched connections and notch-connected composite floors, this thesis presented experimental, numerical, and analytical investigations. Push-out tests were conducted on the notched connections first, and then bending tests and vibration tests were conducted on full-scale composite floors. Finite element models were built for the notched connections to derive the connection shear stiffness. Finally, analytical solutions were developed to predict the internal actions of the composite floors under external loads.
This study shows that the structural performance of notched connections is affected by the geometry of the connections and material properties of timber and concrete. The notch-connected MTP-concrete composite floors showed high bending stiffness but were not fully composite. The floors with shallow notches tended to fail in a ductile manner but had lower bending stiffness than floors with deep notches. The composite floors with deep notches, however, often fail abruptly in the concrete notches. By reinforcing the notched connections with steel fasteners, the composite floor can achieve high bending stiffness, high load-carrying capacity, and controlled failure pattern. The proper number and locations of notched connections in the composite floors can be determined from the proposed composite beam model.
This thesis presented promising results in terms of the static and dynamic structural performance of notch-connected MTP-concrete composite floors. The test investigations added additional data to the current research body and prompted further evolvement of timber-concrete composite floors. The proposed empirical equations for estimating the connection stiffness and strength and composite beam model for predicting the serviceability and ultimate structural performance of composite floors provide useful tools to analyze the notch-connected MTP-concrete composite floors. The design recommendations for MTP-concrete composite floors with notches are provided in the thesis.
Mass Timber Panels (MTP) are a new generation of engineered wood panels that are available in large plane dimensions to facilitate fast floor construction with the obvious environmental benefit of being from a renewable material. In floor construction, concrete slab or topping is often applied over the MTP panels to improve various performance attributes, including structural, acoustic and vibration serviceability. Mass Timber Panel-Concrete (MTPC) composite floor system often consists of a Mass Timber Panel (MTP) connected to the concrete layer with mechanical connectors such as Self-Tapping Screw (STS) and a sound insulation layer in between the MTP and concrete. Lack of design standards and guidelines are the most important barrier limiting wide spread use of this MTPC composite floor system.
The capacity of this type of composite system mostly depends on the strength of the interlayer connection. Also, the allowable floor span is often governed by serviceability performance requirements, such as deflection and vibration, which are directly dependent on the stiffness of the interlayer connection. Usually, connection tests are performed to characterize connection strength and stiffness required for structural design. In this research, three types of MTPs with normal weight concrete, three insulation thicknesses, two screw embedment lengths and two screw angles were tested to characterize connection strength and stiffness. Test results showed that connections with screws at an insertion angle of 30-degree had a larger strength and stiffness than connections with screws inserted at a 45-degree angle. Stiffness appears to be more sensitive to the presence of an insulation layer compared to strength. Overall, 5-15% and 22-34% reduction of strength and 35-50% and 55-65% reduction of serviceability stiffness were noticed for an insulation thickness of 5 mm and 15 mm, respectively. In lieu of testing, analytical models can be developed to directly calculate connection strength and stiffness based on component properties. To that end, two analytical models each were developed for solid and layered timber, for directly predicting the stiffness and strength of a connection with inclined screws and an insulation layer. Usually, connection properties of laterally loaded connection is controlled by the dowel bearing effect of the fastener in timber, but inclined screw connection has a more complex behaviour due to the combined bearing and withdrawal action of the screw. Therefore, in the developed models, both the bearing and withdrawal actions of the screw are considered. The connection stiffness and strength model were validated with the connection tests with a wide range of parameters. It was found that the strength models are capable of predicting the mode of failure of a connection and the load-carrying capacity within 10% of the experimental value, while, the stiffness models are capable of predicting the stiffness of connection to within 18% of the experimental value.
The commonly used Gamma method to design a timber-concrete composite floor has limitations and cannot predict the load-carrying capacity, bending stiffness and failure modes of the composite floor system when there are widely spaced discrete connectors. Therefore, an analytical model has been developed considering the interlayer connector behaviour under the elastic-plastic range along with an acoustic layer between timber and concrete, to predict the capacity, bending stiffness, failure modes and the load-deflection response of MTPC composite floor system. One-way acting composite floor panels were also tested under four-point bending with different configurations to investigate the influence of different parameters and to validate the developed system prediction model. It was found that the model is capable of predicting the capacity of the MTPC composite system within the range of -6% to +26%, bending stiffness within the range of -15% to +10% of the bending test values and the associated failure mode. The Gamma method cannot predict the system capacity, and it tended to over-estimate the bending stiffness on average by 43% and was found not appropriate for MTPC composite system with discrete shear connectors and MTP. This developed connection and system models for MTPC composite floors will facilitate the use of such a system in mass timber construction.