Observations from Vibration Testing of In-Situ Structures

Abstract

Low-frequency floor and footbridge vibration serviceability problems typically arise when the structure is excited in resonance due to a walking excitation and the resulting accelerations exceed human comfort levels. The measures required to resolve an annoying vibration problem after the structure is constructed can be very difficult and expensive to implement. In most cases, the costs of fixing the problem in-situ are much greater than tackling the problem in the design phase, prior to the structure's construction, considering the potential cost to building owners from possible legal expenses, loss of rental revenue, and consultation fees. Design guidance for composite steel framed floor systems and footbridges is available in the AISC/CISC Steel Design Guide Series 11: Floor Vibrations Due to Human Acitivity . Although the current design guidance is generally acceptable, there is a need to continue characterizing the often-complicated vibration behavior of these structures in an effort to refine current design and analysis techniques, particularly as researchers gain a better understanding of behavior by collecting high-quality experimental data on in-situ floor and footbridge structures. This paper presents observations from such efforts to further characterize behavior through experimental modal testing of a large in-situ composite steel office floor and a laboratory constructed multi-span footbridge. While not entirely inclusive, some general observations are noted on the dynamic behavior, problems encountered, and the consistency/reliability of the applied testing/analysis techniques employed by the researchers.