Red Hill Creek Bridge

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.