TIC 2020-09-21 Agenda Front Sheet

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42nd Ave South Bridge In-depth Inspection September 18, 2020 Page 2 section loss at the panel points. Most diagonal members that are in compression have rust along seams where two of the steel beams have been secured together with rivets. The corrosion along the seam is causing the rivet heads to deflect along the diagonal members. Additionally, there is seam rust along most vertical steel members and along sway bracing with areas of rust with minimal section loss. Several sway bracing members have high load impact damage due to oversized trucks striking the overhead members, which have caused upward deflection in flange angles. The observed section loss and deflection in the steel members are within design standards given the age of the bridge but should continue to be monitored to observe if the corrosion or section loss is expanding or becoming an issue. According to the attached TranTech report, the results of in-depth inspection and the subsequent analysis showcase that the deficiencies observed/measured do not require further weight restrictions for the 42nd Ave S Bridge. It is of the opinion of the Professional Engineer who performed the analysis, that if the truck traffic continues to abide by the posted weight, speed, and occupancy restrictions, the deterioration of the bridge will be minimal. However, in the event of a catastrophic event (e.g., earthquake, flood, or major impact damage), the bridge is highly susceptible to damage that could require a full shutdown and further analysis. The results from the inspection and analysis also confirm that the 42nd Ave S Bridge is approaching the end of its service life. Without replacement or major maintenance repairs, it will require more and more restrictions for its continued safe use in the coming years. Maintenance projects have been studied from the past and it has been determined that the cost of repairing the bridge would exceed the replacement cost and a full replacement of the bridge would still need to occur. NEXT STEPS The 42nd Ave S Bridge will continue to receive interim inspections to monitor its concrete piers and will continue to receive annual inspections and biennial fracture critical inspections performed by King County. Public Works staff will continue with the bridge replacement design and explore multiple funding sources to replace the structure. Following receipt of the in-depth inspection, staff continues to believe that this is an important project to pursue diligently. As early as 2016, the City recognized the issues with this important bridge, the magnitude of required rehabilitation, and the scope of a potential replacement project. Projects of this scale historically take years and sometimes decades to develop and fund. As such, the City has been correctly prudent to start the work on the 42nd Ave S Bridge before the end of the bridge's designed service life. Attachments: Bridge Memo Report Bridge Inspection Pictures https://tukwilawa.sharepoint.com/sites/publicworks/engineering/PW Drop Box/01 TIC Agenda/2020 Agenda Items/TIC 09-21-2020/03. 42nd Ave S Bridge In -Depth Report/InfoMemo_42nd Ave Inspection Results_2020-09-21.docx t 0