Strong Return

Two months removed from the sudden collapse of the steel truss Interstate 35W (St. Anthony Falls) Bridge, the Mississippi River Gorge through Minneapolis-St.

Steven Prokopy

Two months removed from the sudden collapse of the steel truss Interstate 35W (St. Anthony Falls) Bridge, the Mississippi River Gorge through Minneapolis-St. Paul was open to boat traffic in time for peak fall colors. In that same time span, the Minnesota Department of Transportation (MnDOT) was moving forward with plans for a new fast track-built bridge.

In late October, more than 80 community members gathered at a northeast Minneapolis hotel to help bridge designers finalize decisions on six specific aesthetic features of the 1,216-ft.-long, 10-lane structure. The collective wisdom and experience shared were incredibly valuable in helping us fully understand the community’s vision for this project, says Linda Figg, CEO of lead designer, Tallahassee, Fla.-based Figg Bridge Engineers Inc., and the visual quality manager for the I-35W bridge project. With this feedback, we’re confident that we can create a bridge that truly reflects the values of the community and entire state. We wanted to design a modern concrete bridge that would fulfill the vision of being the best, safest bridge we could.

The result of the charrette process will be combined with public feedback from recent MnDOT open houses, and is one of the many ways the agency is attempting to allow Minnesotans to help shape the final bridge design. Construction is scheduled to begin in November and be completed by Christmas Eve 2008.

The project represents only the second time MnDOT has used segmental precast. Segments for the state’s first such job Û the Crosstown Reconstruction, located close to the 35W bridge site Û were just beginning to be cast at the end of October. Located at the State Road 62/I-35W intersection, the multi-interchange, all segmental precast construction includes work on six ramps. Figg is doing the construction engineering and inspection on the job.


With segment production scheduled to begin in January 2008 and continue through June, the total number of segments is expected to be approximately 120 in lengths of either 13 ft. 6 in. or 16 ft. 6 in. In early October, the joint venture Flatiron-Manson was awarded a $234 million contract to replace the bridge, with plans to open a St. Paul yard to fabricate segments for barge delivery. Four long-line casting beds will be utilized for the work.

The preliminary design calls for a four-span structure with girders of wide parabolic profile. The 504-ft. main span will have primarily precast segments, plus some cast-in-place construction Û a specification Flatiron-Manson will determine as schedules dictate. The 148-, 248- and 319-ft. approach spans will be cast in place. Flatiron-Manson and Figg insisted a local ready mixed supplier be tapped for the site and casting yard work. (Market leader Cemstone Products had received the nod as of late October.) The yard will likely be on MnDOT property, says Figg. We want a location as close to the job site as possible. That allows us to have the lowest-energy solution.

Designed with a 100-year life, the bridge will bear on eight 70-ft.-tall, cast-in-place piers supported on multiple shafts drilled into bedrock.

Although the design-build team is still finalizing the specs concerning its precast or cast-in-place portions, the 504-ft. main section could represent the largest installation of fully match-cast precast segments in North America and the second-longest overall span of segmental precast. Oakland’s Bay Bridge’s 550-ft. spans are segmental precast, but built with 1-meter closure pours; hence, they are not match cast.

Figg previously worked on what is currently North America’s longest installation of match-cast precast segments Û the New Jersey DOT’s Victory Bridge, which carries Route 35 over the Raritan River and connects the Middlesex County communities of Perth Amboy on the north and Sayreville to the south. The Garden State’s first segmental concrete crossing, Victory Bridge consists of twin structures featuring main span units of 330, 440 and 330 ft., which were built in balanced cantilever and helped gain enough height to provide 110-ft. navigational clearance. The project was completed in September 2005.

Flatiron Constructors of Longmont, Colo. (part of the design-build joint venture with Seattle-based Manson Construction Co.) also has extensive construction experience on major bridges, including work on the I-10 Bridges over Escambia Bay, Fla., a $243 million design-build project built on an accelerated schedule Û as well as a portion of the San Francisco-Oakland Bay Bridge and the Sagadahoc Bridge in Maine, a design-build job designed by Figg.

The Flatiron-Manson and Figg teams’ primary focus was building the best and safest bridge in all aspects of its proposal. Structural enhancements include the use of high performance concrete to provide durability and multiple levels of structural redundancy for a long-lasting bridge that will be economical to maintain. Linda Figg says 6,000-psi, low-permeability concrete with corrosion inhibitors will be used on the I-35W replacement bridge.

In addition, a sensor system will be built into the bridge to allow for easier and more comprehensive monitoring throughout the bridge’s lifetime. An elaborate safety program also will be implemented throughout all aspects of the design and construction process. Our top priority is safety Û both throughout construction and during the entire life of the bridge, says Flatiron-Manson Project Manager Peter Sanderson. We will bring our expertise and proven safety record to bear on every aspect of this project.


The American Segmental Bridge Institute is soliciting abstracts of candidate papers to be presented at the First ASBI International Symposium 2008: Future Technology for Concrete Segmental Bridges, Nov. 17-19 at the Fairmont Hotel in San Francisco. Abstracts on papers covering these symposium categories are being accepted through Jan. 31: Innovative Construction Methods & Erection Equipment; Durability, Maintenance & Sustainability; Developments in Design Codes and Practices; Cable-Supported Segmental Bridges; Seismic Design of Segmental Concrete bridges; Innovative Bridge Types; Segmental Substructures; Rapid Transit projects; Pedestrian Bridges; Signature Bridges and Aesthetics; Reports on Outstanding Projects/Projects Showcase; Design-Build Projects; and, New Materials/Technologies.

Instructions for submitting abstracts are posted at Submissions will be evaluated by the ASBI Symposium Technical Committee, with prospective presenters notified by early March.