TIC 2020-09-21 Agenda Front Sheet

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11111111111111111 TO: FROM: BY: CC: DATE: SUBJECT: aft irks Depa n; ....Han Panne tractor INFORMATIONAL MEMORANDUM Transportation and Infrastructure Committee Hari Ponnekanti, Interim Public Works Director Adam Cox, Transportation Project Manager Mayor Allan Ekberg September 18, 2020 42nd Avenue South Bridge In -Depth Inspection Project No. 91810404 Bridge Results Allan Ekberg, layer ISSUE Provide results from the in-depth inspection of the 42nd Avenue South Bridge. The Committee received a status report in August 2020 on the bridge closure that was necessary for the inspection to be safely completed and the feedback the City received during and after the closure. BACKGROUND Currently, the 42nd Ave S Bridge has a sufficiency rating of 7.56 out of 100, per King County Road Division's inspection. Sufficiency ratings are calculated by a formula implemented by the Federal Highway Administration to inventory the nation's infrastructure, and to determine allocation of federal funds for bridge replacement. Some of the considerations in establishing a bridge's rating include: • Structural Adequacy • Serviceability and Functional Obsolescence • Special Reductions In December 2019, the full Council supported staff's recommendation to perform additional analysis beyond the routine scope of inspection that King County normally performs on the City's bridges. The City contracted with TranTech Engineering for a more in-depth structural inspection in the amount of $39,884.00. This in-depth inspection provides a better understanding of how the bridge steel is performing internally. During the inspection, the 42nd Ave S Bridge was closed to all vehicular traffic to allow the inspectors to safely maneuver on the bridge. The inspection was delayed due to the Seattle Department of Transportation (SDOT) restricting the use of the Under - Bridge Inspection Truck (UBIT) due to the West Seattle Bridge closure and COVID-19 measures. The UBIT inspection was conducted on July 22 and 23, 2020, allowing inspectors access to the steel members under the 42nd Ave S Bridge. The inspectors then used a boom lift on July 24 to access the connection points at the top of the bridge. ANALYSIS The 42nd Ave S Bridge has areas of section loss and corrosion (i.e. an element has lost area from its original design/constructed area, affecting its engineering properties) that had been painted over in the last painting of the bridge. This analysis shows that the corrosion is particularly true along the lower chord and gusset plates. In some areas, the corrosion is becoming active again with minimal 9