Vibration characteristics of cold-formed steel-timber composite flooring systems

Abstract

Recent advancements in the construction industry are pushing for more sustainable residential and commercial buildings. This trend is driven by the need to limit the excessive use of concrete, a building material generally selected due to its relatively low cost and ease of application, particularly in the local backdrop, but with significant drawbacks from a sustainability perspective. Timber is a viable option for construction with a more renewable and environmentally friendly performance. The concept behind composite structural systems is to have the advantages of different materials strategically combined to develop a better-performing component. This can easily be seen in reinforced concrete elements where the tensile properties of steel are combined with the compressive properties of concrete. Similarly, in steel-timber composite systems, timber panels are strategically connected to the top flange of steel beam sections resulting in a highly efficient, lightweight, and relatively slim flooring system. However, the lightweight nature of these floors leads to serviceability issues including vibration and deflection. It is clear from previous studies that when adequately connected and acting compositely, steel-timber flooring systems provide enhanced flexural behaviour. However, the implications of composite action on the vibration characteristics of such floors remain largely unexplored. In this study, the vibration characteristics of steel-timber flooring systems are investigated particularly to their response to variations in the shear connection. An assessment of the resulting range of floor frequencies and their implication on human comfort is presented. A series of test specimens, consisting of timber particle boards overlying cold-formed steel beams, are excited at various predetermined locations. Accelerometers are used to quantify the acceleration of the composite floors at various locations, and the modes of vibration are identified using Fast Fourier Transform (FFT). Following analysis, it was noted that the degree of shear connection does have a small but gradual increase in the natural frequency of the composite floor. Given a higher flexural stiffness, implied by the higher number of screws, an overall percentage increase of 4.026% in natural frequency was measured. This was also verified by an analytical approximation whereby more screws provided a greater flexural stiffness which leads to a higher natural frequency, as observed in the physical testing. Additionally, upper and lower bound values for frequency were calculated whereby the total range amounted to 19.108%, hence the recorded data occupies a significant portion of the theoretical range.