An effective floor serviceability design relies on a proper serviceability criterion, a reliable design method and accurate design values of the mechanical properties of the floor components. Forintek developed a tentative performance criterion to control vibrations in a broad range of wood-based floors in 2000. The criterion proposes to use the combination of 1 kN static deflection and fundamental natural frequency to control vibrations in a broad range of wood-based floors. Forintek’s members requested the development of a methodology for vibration controlled floor design that accounts for as many of the construction parameters involved in wood-based floors as possible. A comprehensive floor model was therefore needed to serve as a benchmark for the development of the desired methodology. A literature review of existing models indicates that none of them can handle all the construction parameters, especially the lateral reinforcements (cross-bridging, blocking, strong-backs, bracing, strapping, etc.) and the use of multi-span continuous joists.
Due to the shortcomings of existing models, Forintek has developed a finite element model for a broad range of wood-based floors. The model accounts for almost all the construction parameters including transverse shear deformations, multi-layered sub-floor and ceiling boards, gaps perpendicular to joists in sub-floors, non-rigid connections, rigid and flexible support conditions, and most importantly, various types of lateral reinforcements including cross-bridging, blocking, strong-backs, bracing, strapping, and multi-span continuous joists. The model was developed for static and frequency analyses for the time being, but is believed to be extendable for dynamic and acoustic response analyses, and stress analysis.
The model was verified using databases consisting of 22 full-size wood-based floors tested at Forintek and other laboratories. The test floors covered a broad range of construction features included in the model. The parameters measured included the mechanical properties of the floor joists and the fastener-to-wood connections, floor static deflections under concentrated loads, and the natural frequencies and mode shapes.
Sensitivity studies were conducted to examine the effects of the mechanical properties of the fastener-to-wood connections on the predicted static deflections and natural frequencies. Based on these studies and the measured mechanical properties of the fastener-to-wood connections, reasonable values were identified for the mechanical properties for these connections used to attach lateral reinforcements or sub-floors to joists. Using these values for mechanical properties of the connections, the measured joist properties and the published properties for sub-floor and ceiling panels as the input, the finite element model predicted the static deflections under concentrated loads and natural frequencies reasonably well when compared with measured values.
To create user friendly software from the model, a pre-processing program was developed to automatically generate finite element mash blocks for wood-based floor systems, and a post-processing program was developed to graphically display the finite element floor model and results. A manual for the finite element floor software was prepared.
In conclusion, the present finite element software for wood-based floors is unique particularly in modelling floors built with multi-span continuous joists and floors having various types of lateral reinforcements. The beauty of the model comes from its exclusive use of measurable parameters including mechanical properties of the reinforcements and stiffness of the connections between joists and reinforcements to achieve good predictions for the static and dynamic behaviour of wood-based floors containing these reinforcements. This special feature, along with others discussed in this report, makes the software a benchmark for the development of a simplified design procedure for a broad range of wood-based floors and a useful tool for wood-based floor performance research and design. In addition, the user-friendly nature of the software makes it a useful tool for assisting wood industries to develop new wood-based floor construction products and systems.
The current version of the software is limited to static and frequency analyses, but it can be extended for other applications such as stress analysis and analysis of responses to dynamic loading and sound.