I-35W Contract Awarded, Conceptual Design Unveiled
The Minnesota Department of Transportation yesterday awarded a $243-million contract for rebuilding the I-35W bridge in Minneapolis to a team including Flatiron Constructors, based in Longmont, Colorado, in joint venture with Seattle-based Manson Construction. Also on the team is Orlando-based Johnson Bros., in a support role, and Figg Bridge Engineers, of Tallahassee, Florida, as lead designer. The new highway span will replace one that collapsed on August 1, killing 13 people and injuring 100.
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At a press briefing, Figg president Linda Figg invoked “arches, water, reflection” as the theme for the new 1,216-foot-long, 10-lane concrete bridge with a 504-foot-long pre-cast segmental main span clearing the Mississippi River. Flatiron-Manson project manager Peter Sanderson added that the team hopes to start work on the St. Anthony Falls Bridge, as it is called, by November 1 and complete work by Christmas Eve 2008. “Our top priority is safety—both throughout construction and during the entire life of the bridge,” he said.
The bridge, designed with a 100-year life, will support the main span on four 70-foot-tall piers supported on multiple drilled shafts into bedrock. Figg emphasized that there will be “no fracture-critical members” in the redundant design. Each of the twin bridges will be 90 feet 4 inches wide, allowing room for future bus rapid transit or light rail networks.
According to the proposal, the main span pre-cast segments will be placed by a barge-mounted crane, while the 330-foot-long and 260-foot-long connecting continuous concrete spans, as well as one 121-foot-long end span, pre-stressed and post-tensioned, erected on falsework. The proposal also includes a state-of-the-art sensor and monitoring system and the possibility of monumental markers at the entrances on either side.
Community participants in a one-day design charette workshop to be scheduled this month will choose from two pier options—one where the pier columns taper outward at the tops and bottoms and flow into the curvature of the main span, or one with straighter piers with blue coloring along their lengths. They will also choose between a white and sandstone coloring for the overall bridge, types of railings and types of LED lighting.
Most of the components of the concrete bridge outlined in the Flatiron-Manson and FIGG proposal will be built in Minnesota, with local materials and workers, according to Sanderson. The project will open a site later this month in St. Paul to begin pre-casting the concrete components, which will be delivered by barge to the I-35W Bridge site.
A version of this article first appeared on McGraw-Hill Construction’s enr.com.
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