943 Wisconsin bridges are 'structurally deficient'; engineer explains what it means & why it's not an immediate concern

MILWAUKEE (CBS 58) -- The collapse of the Key Bridge in Baltimore has refocused attention on infrastructure needs throughout the country.

Nearly 1,000 Wisconsin bridges were classified by the Federal Highway Administration as "structurally deficient," including many in the southeast part of the state.

But the director of UWM's Structural Engineering Laboratory was quick to say that classification does not mean a bridge is in immediate danger of collapse.

Still, the Baltimore bridge collapse has engineers around the country studying their structures closely.

UWM's Dr. Habib Tabatabai said, "It actually has a huge influence."

For the past two days, civil and structural engineers across the country have pored over the Baltimore bridge collapse, looking for any information that can prevent a similar tragedy in the future.

Dr. Tabatabai told us, "Anytime that a major collapse happens, it doesn't have to be on the waterborne-type disasters, a major wind event, earthquake, and so on, then the industry --the academia, governing standards-- all change and they study those."

Port Milwaukee told us ships sailing into Milwaukee are smaller than those in the port of Baltimore: the same length, but half the width.

Another big difference: the Hoan Bridge's support structures are not in the water and cannot be damaged by ships.

The Port Authority oversees the water, but not the Hoan Bridge. That’s owned and operated by the state’s Department of Transportation.

WisDOT is responsible for maintaining the majority of bridges throughout the state of Wisconsin, including the I94 bridge over Mitchell Boulevard, which is one of the state's most traveled bridges that is structurally deficient.

Bridges have several components: the road deck and girders carry vehicles up top, and piers and abutments support from below.

Federal law requires inspections every two years, where each component is rated from 0 to 9. A 9 rating means a component is new. When a component reaches level 4, it gets into the structurally deficient category.

Of the more than 14,000 bridges throughout Wisconsin, the Federal Highway Administration identified 943 in 2023 that were structurally deficient.

However, Dr. Tabatabai said, "It does not mean that there is anything in terms of risk of collapse or harm to people."

Different bridge components have different life spans.

Tabatabai said road surfaces typically last 40-50 years before they require repair or replacement. And he said entire bridges can last much longer with proper maintenance. "We design modern bridges for about 70, 75 years as a design life."

WisDOT was unavailable for an interview on the state's inspection process.

But a spokesperson sent a statement that said in part, "WisDOT’s rigorous inspection program allows for routine inspections to assess the condition of bridges throughout the state and ensure each structure is safe for the traveling public."