TIC 2020-09-21 Agenda Front Sheet

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E n IIV 42nd AVE S BRIDGE INSPECTION EXECUTIVE SUMMARY Date: September 9, 2020 To: City of Tukwila From: Kash Nikzad, PhD, P.E. Re: 42"d Ave S Bridge Inspection Executive Summary TranTech Engineering (TranTech) and Fickett Structural Solutions (Fickett) teamed up to provide an in- depth fracture critical inspection of the 42nd Avenue South Bridge under City of Tukwila (Tukwila) Contract Number 20-030. The field inspection was performed by Fickett on July 22-24, 2020. The inspection details are presented in Appendix A and have been used to form an opinion of the ability of the existing truss to continue to safely serve with continued proper management and monitoring. Background The 42nd Avenue South Bridge is a 3-span 280-foot-long bridge built in 1949. The bridge is composed of a 220-foot-long fracture critical steel thru-truss main span with 30-foot-long concrete T-beam approach spans at each end. A critical feature of the bridge is it's extreme 38° skew, a design aspect that has contributed to its current condition rating. The existing bridge has a sufficiency rating of 7.53 and is both Structurally Deficient and Functionally Obsolete. The Sufficiency rating (SR) is a method of evaluating highway bridge data by calculating four separate factors to obtain a numeric value which is indicative of bridge sufficiency to remain in service. The result of this method is a percentage in which 100 percent would represent an entirely sufficient bridge and zero percent would represent an entirely insufficient or deficient bridge. The four factors are: 1. Structural Adequacy and Safety 2. Serviceability and Functional Obsolescence 3. Essentiality for Public Use 4. Other Special Reductions for bridges where the first three factors sum to less than a score of 50. The SR is not a direct indication of the service life remaining but is an evaluation of the condition of the bridge, how it fits the route it serves, and what kind of demand route puts on the bridge. Historically, the SR has been used as a funding eligibility measurement and ranking tool. In addition, structural deficiency has been given priority over functionality and risk -based deficiencies in funding decisions. As long as the bridge is managed properly, it can be safely used. This management of the structure usually means a reduction in service to the travelling public. As a result, the 42nd Avenue Truss has been load -restricted to limit additional damage from the high volume of trucks crossing the bridge each day. The current SR is a combination of its functional problems, how important it is to the traveling public, and its deteriorating condition. Analysis shows that the 42nd Avenue Truss is at risk during a seismic event, but in order to seek funding from the Local Agency Bridge Program, Tukwila must show condition issues. This has been done through analysis and inspection. While the bridge's condition does not indicate imminent collapse, it does point to the risk of collapse during a major seismic event and/or the continued accumulation of fatigue stresses in the fracture critical bridge which at some point may result in a fracture collapse. A fracture critical bridge is constructed of steel and has only two major load carrying components. In the TranTech Engineering, LLC 365 — 118t Ave SE, Suite 100, Bellevue, WA 98005 425-453-5545. Fax: 425-453-6779 11