We’ve been asked a lot about the giant chains hanging from the new Memorial Bridge. Some have speculated that they are a backup safety measure, a temporary feature, or simply an aesthetic feature, but the chains are actually an elegant answer to a functional need.
The previous iteration of the Memorial Bridge was one of the first vertical center-span lift truss bridges in the country, and the tradition of groundbreaking features continues with its recently-opened successor. The large chains were actually manufactured as anchor lines for large ships, adding a design element to the bridge that ties in with the industry that will be passing under it for years to come.
So what are the chains for?
In a word, balance. The middle span weighs 2.5 million pounds, and the massive concrete counterweights just as much, at 1.25 million pounds each. Unfortunately, the much smaller lifting cables also weigh a lot—about 60,000 pounds. As the center span raises and lowers, the only weight changing on each side of the sheaves (pulleys) are from the shifting length of the cables. The massive chains were employed to offset that weight, making them an essential asset to the functionality and efficiency of our new bridge.
Always in balance. A functional yet elegant solution.