A pair of steel platforms that workers used while adding carbon-fiber wrap to the cracked West Seattle Bridge were lowered onto barges in the Duwamish River this week to be taken away.

The removal signals that work to stabilize the bridge and prevent a collapse is nearing an end. A total of four platforms were hung this summer, nearly 140 feet over the water, by repair contractor Kraemer North America.

The carbon lends stiffness to the concrete girders and provides a stronger surface to bolt anchor blocks inside the hollow bridge, where new tensioning cables reinforce weak areas of the 590-foot-long mainspan.

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The Seattle Department of Transportation closed the bridge March 23, when cracks in the concrete girders began to spread rapidly.

With the bridge now stabilized, city consultants will engineer a permanent repair expected to last 15 to 40 years, aiming to restore six lanes of traffic in 2022. Before the closure and coronavirus pandemic, 120,000 drivers and transit riders crossed daily, making it Seattle’s busiest city-owned bridge.

The repairs are estimated to cost $47 million, but the city could spend more than $100 million by the time road-detour projects, retrofits of the lower swing bridge, and preliminary design of a future replacement high-rise bridge are complete.