King County is consulting with federal, state, and private sector experts to try and figure out how to safely reopen a nearly new bridge it closed last month under emergency conditions.
The nine-year-old Tolt Hill Bridge crosses over the Snoqualmie River and is southwest of downtown Carnation. County officials closed the bridge on June 16th after the engineers learned that the bridge’s design might not be strong enough to hold up traffic. The emergency closure was needed after a recalculation of the math involved in the design, said Brenda Bower, King County’s Road Services Director.
Now, the county is trying to figure out if it can reopen the $26 million bridge to limited traffic, but keep large trucks and other heavy vehicles off it until a permanent solution is reached.
Carnation residents are frustrated with detours and delays which have turned short drives into town from just a few miles into 25 miles or more around trips.
Bauer said the county might never have found the problems if it had not been for the collapse of the 35W bridge in Minneapolis, Minnesota in 2007. That accident, along with the expected arrival of heavier trucks on the nation’s highways prompted the Federal government to require a design review of the nation’s bridges by 2022, along with using updated methodology of calculating bridge strength.
A review was done on the Tolt Hill Bridge which took inspectors back to the original design by an engineering company before the plans went to the contractor who constructed the bridge.
Based on the review, they found the bridges bolts appear to be too light, too few, and gusset plates that connect beams, other structural members, together are not thick enough.
The bridge had been carrying traffic, including many heavy dump trucks and other large vehicles, without incident for nine years. The bridge sees 3,000 vehicles crossing a day on average, more than a million vehicles each year.
County engineers inspected the bridge every two years, and never found any bolt cracking, plate bending or deflection in the bridge. Bauer notes there may not be a sufficient margin of safety at certain connection points where various bridge parts come together.
The county hopes to have some answers on what comes next later in the week. While some residents are skeptical the bridge will ever be reopened, Bauer promises there will be a fully functional bridge in the future.