SDOT not worried about concrete slabs under Magnolia Bridge

Slabs of concrete likely fell from the Magnolia Bridge, but a Seattle Department of Transportation (SDOT) official said it’s nothing to be worried about.

Bruce Carter, a member of the Friends of Smith Cove Park, said he was looking for potential parking spaces for Smith Cove Park on June 16 inquired when he happened upon two concrete slabs, roughly the size of his size-14 shoes, under the bridge in the area immediately west of 23rd Avenue West. He emailed SDOT, asking whether safe concrete bridges should lose such large pieces of concrete.

“If it fell from beneath the deck and hit someone on the head, I expect there would be a substantial wrongful-death claim,” Carter wrote in an email. “If we have a big earthquake, can we expect even more to fall in light of the liquefaction underlying the site?”

John Buswell, SDOT’s head of Roadway Structures, said the piece of concrete Carter found is likely due to a process called “spalling,” which is the result of aging: “It occurs on all older steel and concrete bridges but does not affect the strength of the structure.”

Buswell said he based his conclusions on Carter’s photos, using his more than 20 years of performing inspections on the Magnolia Bridge and past experiences with spalling concrete. 


Still safe to use

Buswell said SDOT bridge maintenance personnel were working on the Magnolia Bridge June 15 through 17; it was last inspected March 2015. 

He said he asked Carter for more specific information about the location of the concrete spall but did not hear back. Without a specific location, Buswell said he couldn’t say for certain whether the structural concrete had been repaired, fell from the bridge or was removed by inspectors or other bridge maintenance personnel. Buswell said crews did not note any significant new issues with the bridge during the maintenance work. 

Buswell said Seattle’s bridges are exposed to the harsh Northwest environment, which includes salt spray from Elliott Bay. The chloride from seawater spray corrodes the reinforcing steel, causing it to expand and pop off relatively small pieces of concrete, he said.

“A small loss of the concrete that covers reinforcing steel does not significantly weaken the bridge, and we clean and patch these areas before they become a problem,” Buswell said.

Buswell said the Magnolia Bridge has one of the greatest exposures to prevailing winds from the southwest and is adjacent to Elliott Bay. 

“Our bridge engineers inspect the Magnolia Bridge twice each year, with one of those inspections using our Under-Bridge Inspection Truck, which allows them to reach areas that are very high off the ground,” he explained. “These engineers are instructed to look closely for any loose, spalled concrete, especially over vehicle and pedestrian areas. The engineers will typically drop the loose concrete pieces safely to the ground below, which may explain the concrete [Carter] noted. We then patch the concrete on the bridge to protect the steel.”

Buswell said there are no safety concerns on the Magnolia Bridge and that it is safe for legal-weight vehicles.

“Long before the bridge would be unsafe for use, we would restrict trucks and buses from using it and eventually close the bridge,” he said.


Future of the bridge

The Magnolia Bridge was built in 1929 and was listed third on SDOT’s replacement priority list back in 2013.

Buswell said bridge replacement prioritization takes many factors into consideration, including available funding. Currently, he said, SDOT plans to replace the Yesler Way, Post Alley and Fairview Avenue bridges. 

He said SDOT has proposed funding to further refine the replacement solution for large bridge replacement projects, including the Magnolia Bridge, in the transportation levy, being reviewed at press time by the Seattle City Council for the November ballot. 

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