200 nearly century-old suspension cables are being replaced on the Ambassador Bridge

Original suspender cables are in the midst of being replaced on the Ambassador Bridge — and work is set to be finished in 2024.

Randy Spader, vice-president of operations at the Detroit International Bridge Company, says 200 of the bridge's 300 main span cables are being swapped out — and that work began last year.

The first 100 ropes were replaced between 2003 to 2007, he says.

The bridge was originally erected across the Detroit River, linking Windsor and Detroit, in 1929 — meaning some cables are roughly 94 years old.

According to Spader, other than age and preservation, the work is not in reaction to anything specifically.

"This is planned maintenance and part of our Restoring the Ambassador Bridge [plan]," he said.

On the bridge's website it says repairing ropes with broken or deteriorated strands assist maintaining the condition of the "superstructure," and that galvanized ropes are replacing old cables that contained lead paint.

Goods worth $300M pass over bridge every day. But the ongoing work is expected to cause "minimal to no disruption" to commercial and commuter and passenger traffic.

What's the risk?

Spader says the cable replacements do not compromise, in any way, the overall structural stability of the bridge — and that the work is closely monitored on an ongoing basis.

"This project, like all projects done on the Ambassador Bridge, is developed and monitored by our engineering firm Modjeski and Masters."

Cancan Yang's research is largely focused on bridge engineering, and she says it's crucial to have a rigorous bridge health monitoring system in place during replacement.

"The real-time monitoring on the behavior of those remaining structural components and just to see whether they are overstressed while they are taking out one of the hangars," said the assistant professor of civil engineering at McMaster University.

Yang says suspension bridges are typically designed to maintain a decent level of structural redundancy, shifting service loads to other components that are acting under full capacity.

"I think every bridge component has its service life or structural life. So once we reach that point and it's very often that the bridge will go through some replacement or have occasional work."

According to Yang, suspension bridges normally have a service life of 100 years or more, so some sort of structural deterioration is to be expected.

"That means their structural properties will not be as good as in the beginning …  and so this will also change the overall structural integrity."

And with the bridge's first 100 cables being replaced nearly 20 years ago, Yang says it should have provided them with information on the remaining ones that are in the process of being swapped out.

"I believe they have done some rigorous evaluation where they're testing on those members because this will offer very valuable insights into the capacity of the overall bridge."