Virginia Tech vibration study aims to make footbridges better for pedestrians
For Mehdi Setareh and his research team, the simple task of walking across a pedestrian bridge can help make future bridges better and safer for people.
At issue for Setareh, a professor in the School of Architecture + Design in Virginia Tech’s College of Architecture and Urban Studies and founder/director of Virginia Tech’s Vibration Testing Lab, is the vibrations caused by footsteps.
“Every structure has a natural frequency. This is the speed at which it can freely vibrate when it is hit by a force,” Setareh said. “When the frequency of the force and the natural frequency of the structure are close to each other, a condition called resonance can occur, which results in large amplitudes of vibration.”
A nationally recognized expert on structural vibration, Setareh has focused on using technology to study and enhance the interplay between structural design and vibrations.
Excessive vibration makes a pedestrian bridge uncomfortable for the user, and it can be expensive to fix. This research can help by providing a better understanding of resonance and how architects and engineers can better design bridges to avoid excessive vibrations.
What that means is Setareh needs a lot of volunteers willing to walk across a pedestrian bridge. For several years, he has turned to his students for help. They obliged, walking across the footbridge between the University Gateway Center on University City Boulevard and its parking garage.
As the team gathered more data, researchers realized they also needed to have groups walk in unison across the bridge, comparing the vibrations created with the more random patterns of people walking normally.
So he called in the Virginia Tech Corps of Cadets.
Cadets learn to march in unison on the day they arrive at Virginia Tech and practice military drill throughout their cadet careers. So on a recent Saturday afternoon, 30 cadets with the Highty-Tighties, the corps’ regimental band, showed up at the University Gateway Center and made 72 passes across its footbridge.
Setareh’s research team used a series of vibration sensors mounted at the center of the bridge to map the cadets’ actions, including the numbers of steps it took them to cross the bridge and their impression of the vibration they felt as they marched.
“We have found that as the number of pedestrians increases, the footbridge vibrations do not increase proportionally, mainly due to the interactions between the human bodies and the footbridge,” he said. “The tests with the cadets will enable us to better understand this phenomenon in an attempt to make more accurate predictions of possible vibrations of footbridges under the most critical conditions.”
Setareh’s research team includes Mohammad Bukhari, a graduate student in mechanical engineering; Matthew Tiller, a research associate in the School of Architecture + Design; Jiang Li, a post doctoral associate in the School of Architecture + Design; Abhiyani Solanki, a graduate student in civil engineering; Kaushik Panchal, a graduate student in civil engineering; and Yuxin Ren, a junior majoring in architecture.