Retrofitting Steel Joist Supported Footbridges for Improved Vibration Response: Fid-Bau Portal

Retrofitting Steel Joist Supported Footbridges for Improved Vibration Response

Avci, Onur

The main objective of this paper is to determine the possible increase in natural frequencies of the two joist supported laboratory footbridges when bottom chord extensions are installed in an attempt to reduce annoying floor vibrations. The results with bottom chord extensions installed after the concrete placement are compared to results when the bottom chord extensions are installed prior to concrete placement. Results from the static and dynamic tests on the single span footbridge indicate that installing the bottom chord extensions to the joists after concrete placement and with the center of the span jacked up increases the flexural stiffness and fundamental natural frequency considerably, but not as much as installing the bottom chord extensions before the concrete placement. For the three span footbridge, installing the bottom chord extensions also increases the flexural stiffness and fundamental natural frequency considerably, but there is no distinctive advantage of installing the bottom chord extensions before the concrete placement. For both of the footbridges, the magnitude of the increases in natural frequencies is sufficient to consider the installation of bottom chord extensions as a remedy to stiffen (and retrofit) a floor and reduce floor vibrations due to occupancy movements.