A damping system to keep pedestrian traffic from causing excitation of a popular footbridge
The Red Hill Creek Bridge is a pedestrian bridge that links the city of Hamilton with the shore of Lake Ontario. Spanning 220 meters, it allows walkers and cyclists to safely cross over 12 lanes of highway traffic, and serves as a key link in a large network of recreational trails that crisscrosses Southern Ontario.
The bridge’s engineers, McCormack Rankin Corporation, faced numerous design constraints due to the structure’s location and the sensitivity of Red Hill Creek and the surrounding wetland. One notable concern was that the structure could be vulnerable to excitation from pedestrian footfalls, especially if large groups of people were using the structure at the same time, as in a running race. The designers engaged us to create a damping solution that would keep the bridge comfortable for users.
The Z-shaped bridge includes three discrete spans. Our vibration-mitigation approach included five separate tuned mass dampers (TMDs): the two longer spans each received two TMDs, while the shorter south span only required a single device. All five were vertical dampers, each containing a two-tonne mass. The mass inside each damper was capable of moving in response to pedestrian footfalls, but constrained by a set of vertical springs uniquely tuned according to the TMD’s location in the bridge’s structure. In each case, the springs were tuned such that the mass inside the damper would oscillate at the same frequency as the bridge’s own natural frequency – effectively mitigating the movement caused by even a large number of walkers or runners.
The bridge’s structure was carefully crafted to reflect Hamilton’s unique qualities: steel to acknowledge its industrial history, red as a nod to the clay of the Red Hill Valley, and a unique tilted arch to visually differentiate Hamilton from surrounding areas. We delivered a TMD solution that created comfortable conditions on the bridge and protected the designers’ aesthetic vision while avoiding costly structural changes.
The Red Hill Creek Bridge has been operating successfully since it opened in 2010. It quickly became a point of pride for Hamiltonians, and a favourite link for local walkers, cyclists and trail runners. It was awarded the outstanding civil-environmental engineering project of the year for Hamilton-Halton by the Ontario Society of Professional Engineers, as well as the Ontario Public Works Association’s Project of the Year Award in the Structures Greater than $10 Million category.