Vibration Serviceability of Cold-Formed Steel Floor Systems

Abstract

Excessive vibration in response to human activities has been a significant problem associated with lightweight steel floor systems, especially cold-formed steel (CFS) floors. Methods for accurately predicting these vibrations and evaluating floor systems are not readily available to the design community. The limited amount and complexity of research on the vibration serviceability of lightweight steel floor systems have shown an urgent need for further investigation.

The objective of this research is to evaluate how human walking affects the performance of lightweight steel floor systems. Four important aspects that influence floor vibration performance are investigated: rotationally restrained floor joist ends, structural properties of CFS floors, human-structure interactions, and the applicable design guidelines.

The investigation was carried out using an analytical approach in which CFS floor systems are modelled by equivalent orthotropic plates, and the equivalent structural properties are determined by using the Rayleigh method. The method of finite integral transform is extended to obtain the exact series solutions of the bending and vibration of orthotropic plates with rotationally restrained edges. The analytical/numerical results are compared to the results obtained in previous methods and experimental investigations. Then, the significant effects of human occupants on the dynamic properties and responses of lightweight steel floors are examined through the proposed damped plate-oscillator model, which determines frequencies and damping ratios through analytical analysis of coupled floor-occupant systems. The predicted results are compared with previous test results. Three loading models--moving force, moving damped-oscillator, and moving and stationary damped-oscillators are subsequently proposed to obtain the dynamic responses of floor systems to human walking. The analytical results from the three models are compared with the previous test results. After that, parametric studies are conducted on the effects of step frequency, damping ratio, human-to-structure mass ratio, and walking path. The foregoing investigations provide a comprehensive understanding of the dynamic performance of lightweight steel floors affected by human walking. Finally, design guidelines are developed for lightweight CFS steel floors in residential constructions. The floors are classified into three categories based on their fundamental frequencies, i.e. low-, mid-, and high-frequency floors. For each category, the corresponding design criterion and method are proposed.

It is the author's desire that the contributions made in this thesis research help engineering practitioners better understand the dynamic responses and vibrational characteristics of lightweight CFS floor systems, particularly on human-structure interactions and ultimately lead to the efficient design of lightweight CFS floor systems that resisting the vibration induced by human walking.