Nov 12, 2015

Precast Concrete Superstructures Used to Construct Seattle's Elliott Bay Seawall

The new seawall structure consists of a cast-in-place support slab with custom precast concrete face panels, precast concrete Z-superstructure segments and precast sidewalk panel

Oldcastle Precast seawall panels

Oldcastle Precast of Auburn, Wash., was selected by the Joint Venture Team of Mortenson-Manson, general contractor/construction manager (GC/CM), to supply precast concrete Z-shaped superstructure segments and 20-ft-tall seawall face panels for the city’s new $371-million Elliott Bay Seawall Reconstruction Project at the waterfront in downtown Seattle.

The city of Seattle Department of Transportation’s Elliott Bay Seawall Project, part of Seattle’s Waterfront Program, determined that the 100-year-old seawall needed to be replaced. Built between 1916 and 1936, the failing wall suffered significant timber decay and deterioration of the structure from continued exposure to storm waves and tides, including damage from the magnitude 6.8 Nisqually Earthquake.

Acting as a retaining wall between Elliott Bay and the waterfront, the new seawall structure consists of a cast-in-place support slab with custom precast concrete face panels, precast concrete Z-superstructure segments and precast sidewalk panels.

To successfully manufacture the contracted precast seawall components, Oldcastle Precast worked closely with Mortenson-Manson to customize the design and engineering of the fascia panels and specialty Z-superstructure segments essential to the seawall’s stability. The Z-superstructures were a vital structural component, acting as the concrete backbone of the new seawall’s cantilevered sidewalk.

In all, 400 precast concrete Z-superstructure segments (8-ft wide by 9-ft tall, that extend 13-ft) and 400 precast concrete fascia panels (8-ft-wide by 20-ft-tall with a thickness of 15 in.), with various architectural finishes, were manufactured and shipped by Oldcastle Precast-Auburn.

Oldcastle Precast’s precast solution has improved constructability, accelerated the construction schedule and overcome the demanding challenges of the unique seawall project. Constructing Elliott Bay’s Seawall in this cuustomized manner provided an efficient and long-lasting solution for the city of Seattle.

Funded mostly by a 30-year $290-million bond measure that voters approved in 2012, the Elliott Bay Seawall Project, from South Washington Street to Virginia Street, is scheduled for completion in mid 2016.

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