Modal testing of multi-bay steel-framed floors

Steel-framed floors can experience vibration levels objectionable to the occupants. Excessive vibration is commonly induced by regular occupant actions, such as walking or mechanical equipment. Vibration evaluation (i.e., vibration level measurement for typical activities; identification of natural frequencies and damping) can be used in such facilities to assess the serviceability of the floor system. Full modal testing of the floors provides additional insight into the dynamic behavior and possible remedies. Modal testing of a floor presents a similar set of difficulties as other high stiffness, high mass structures such as bridges and buildings. Additionally, floor testing has it's own set of unique modal testing needs. Previous efforts have developed protocols for vibration testing on laboratory floor systems. The laboratory floors are not completely representative of actual construction methods. The work in this paper will discuss the experiences from performing a modal test on a multi-bay office-building floor. The discussion includes an assessment of the most suitable excitation and response measurement methods to estimate high quality frequency response functions. The testing procedures that were found most effective for the multi-bay floor will be compared to recommendations in previously published protocols in an effort to augment the technology. The paper concludes with an assessment of the modal testing techniques for multi-bay steel-framed floors based on this experience.