Third Street Bridge inspection finds widespread corrosion; Pier 9 undermining flagged as urgent

Kale J, the presenter named during the council briefing, summarized findings from the Third Street Bridge inspection and described extensive corrosion, failed joints and localized undermining that will require repair work.

The bridge, built in 1936 and rehabilitated in 1985, is a complex four‑unit structure with a curved north span, a river crossing, a span over BNSF tracks and a fourth unit on the south end. "This bridge was built in 1936," the presenter said, and he outlined how water and salt infiltrating failed joints have driven deterioration in multiple components including the deck, girders, bearings and piers.

Why it matters: the inspection identified elements that reduce the bridge’s structural redundancy and could concentrate loads on aging members. A load rating completed last summer shows the bridge "still remains structurally sound," the presenter said, but he cautioned that certain elements need near‑term repair to preserve capacity and avoid more extensive future work.

Key findings and immediate needs

- Deck joints and drainage: The presenter said many joints had failed and that most joints were repaired over the summer, but trapped water from the north‑end superelevation has caused salt infiltration and localized deterioration, prompting installation of bridge drains.

- Girders and pack rust: Water trapped between built‑up steel members has produced "pack rust," swelling bearing stiffeners by up to 1.5 inches in places and in some locations causing rivet failures and surface pitting, which reduce local structural capacity.

- Pin‑and‑hanger system: The pins were evaluated in 2021 and are scheduled for follow‑up ultrasonic inspection in 2027; the presenter said the pins themselves showed no immediate concern.

- Bearings: Both fixed and expansion bearings show problems. Rocker bearings were undermined in a number of locations; work on Piers 3 and 4 was completed last year, and additional bearing work is included in a 2026–2027 repair program. Several expansion bearings in Unit 4 have almost exhausted their permitted movement, increasing the risk that thermal forces will be transferred into the deck or substructure.

- Pier repairs and methods: Pier 3 required jacking the superstructure, removing loose concrete, repairing exposed rebar and applying a fiber‑reinforced polymer mat; the presenter said similar methods will be used on other piers.

- Pier 9 urgency: The presenter called out Pier 9 as an area of immediate concern, saying, "it's measured about 6 in of undermining underneath that bearing pad," and recommended that Pier 9 be prioritized for repair using the same jacking and rebar‑repair sequence used at Pier 3.

What the city will do next

The city engineer told the council staff will confer with partners, assemble an action plan and return to the council in the spring with recommendations and a timetable for repairs. The presenter noted some repairs involve work in the BNSF right‑of‑way and that specialized ultrasonic testing will be required for some follow‑up inspections.

The briefing closed with no council questions at the time; the council will consider the staff action plan when it returns in the spring.