Clifton Forge Pedestrian Bridge
Clifton Forge, VA
Structural Design and Field Testing
The Clifton Forge Pedestrian Bridge located in Clifton Forge, Virginia was designed and constructed by a group of architecture students at Virginia Tech School of Architecture and Design as part of a community service project. The footbridge crosses over a creek and is supported at one end by an existing concrete retaining wall. The footbridge was prefabricated in three segments consisting of a bridge, a hub, and a ramp section. They were shipped to the site and assembled together. Due to the architectural requirements, the bridge span/depth ratio is about 66, which has resulted in the footbridge to be susceptible to vibrations due to human movements.
A number of static and dynamic tests by the VTL research team during the construction and after the completion of the structure were conducted. These included: (1) modal testing and analysis, (2) measurements to evaluate the effects of human-structure interactions (HSI) on the footbridge, and (3) walk tests and analysis.
From these tests the dynamic modes of the footbridge that may be susceptible to excessive vibrations due to human movements were identified. It was also found that the presence of humans resulted in a decrease in the natural frequencies of the first two modes of vibration and an increase in their damping ratios. The generated vibrations due to the walk tests were subjectively evaluated by a number of people. These results along with the results of the modal tests were compared to the available guidelines and standards and they were found to be consistent. From the result of this study, it was concluded that if an individual walks across the footbridge at a random pace, the generated vibrations will be within the acceptable range.