Missouri’s failing bridge network is undergoing a rapid-fire turnaround, thanks to an unprecedented program that has replaced hundreds of bridges in the last year alone.
The state has opened, on average, more than one repaired or new bridge per day this year. And the $685 million program is more than a year ahead of schedule.
Credit the state Department of Transportation’s Safe & Sound Bridge Improvement Program, an aggressive initiative that aims to replace 802 of Missouri’s worst bridges in five years.
|The Safe & Sound embraces Accelerated Bridge Construction techniques.|
The first repaired bridge opened April 23, 2009; the 500th bridge opened on Tuesday (Aug. 9).
Safe & Sound is the largest bridge rehab and replacement project in Missouri’s history. The state has 10,249 bridges—the seventh highest total in the nation. About 1,200 are in poor or serious condition.
MoDOT unveiled Safe & Sound in September 2006 to address many of them.
As of last week, the program was more than 60 percent complete and on track to finish by the end of 2012, officials said. The original deadline was Oct. 31, 2014.
|Before (left) and after photos show one of hundreds of bridge replacement projects completed under Missouri’s Safe & Sound Bridge Improvement Program.|
“The rate at which we have been completing these projects is incredible,” said Project Director Ken Warbritton.
“This year alone, we have been opening more than one bridge per day on average. By the end of the year, we plan to have built more than 350 new bridges, making this the busiest bridge year in Missouri history.”
The ABCs of ABC
The Safe & Sound program embraces the use of Accelerated Bridge Construction (ABC), which leverages both design-build contracting and Prefabricated Bridge Systems and Elements (PBES) technology. The goal is to deliver good bridges at great value and minimize public inconvenience through increased construction speed and a flexible schedule.
The Federal Highway Administration (FHWA) is a major backer of ABC projects, saying they reduce on-site construction time, environmental impact and cost while improving worker safety and product quality.
Using prefab components manufactured off site allows work to proceed more quickly along multiple tracks—and, in Missouri’s case, in multiple work zones. Rapidly expanding technologies have made it possible for bridge components, assembled composites of components, and sometimes even entire bridges to be prefabricated.
Federal Highway Administration
|The world’s largest crane lifts a pre-cast 850-ton truss into place in Connecticut.|
Most of the construction work is done off-site, usually in a nearby staging area, and the new bridge superstructure is lifted or ‘rolled’ into place. While components are being cast and assembled off site, the old bridge can be demolished and the site prepared.
In 2003, the state of Connecticut lifted a 320-foot-long, 850-ton pre-assembled truss bridge—built alongside the bridge site— into place with what was then the world’s largest crane.
In Missouri, the original Safe & Sound model called for a design-build-finance-maintain contract, under which one team would have financed the project, completed design and construction within five years, then maintained the bridges for an additional 25 years.
After receiving proposals, however, the state deemed that plan unaffordable due to the credit market crisis and devised the current plan. The state chose 248 bridges for rehabilitation and contracted that job using a modified design-bid-build approach. More than 100 of those structures were completed in 2009.
The remaining 554 bridges—all slated for replacement—were packaged in a design-build contract that was awarded in May 2009 to KTU Constructors, a joint venture of Kiewit Western Co. (Omaha, NE), Traylor Bros. Inc. (Evansville, IN) and United Contractors Inc. (Great Falls, SC). They are joined by design partners HNTB Corporation (Kansas City, MO) and The LPA Group, Inc. (Columbia, SC).
Using 40 contractors and battalions of subcontractors, fabricators and materials suppliers, KTU completed 330 bridges by the end of 2010 (114 of them, including 90 total replacements, in one 103-day period) and scheduled more than 300 for construction in 2011.
One box culvert bridge was replaced in 11 days. The fastest single-span bridge was constructed in 23 days; the fastest four-span construction, in 33 days. The average closure statewide for replacement has been about 40 days—about half the usual time required, according to MoDOT.
Under the design-build contract, KTU Constructors will recycle 9,000 tons of steel and 148,000 tons of concrete.
Replacement and Waterproofing
KTU has devised a variety of bridge replacement strategies, including the use of cored slab, box beam, steel girder, flat slab, and reinforced concrete box culverts. For 493 “Form R Bridges” on low-volume routes, the bridges will be closed during construction. The remaining 61 “Form T Bridges” will require complete closure, staged construction, or bypasses to minimize impacts to travel.
Waterproofing was considered critical to the 215 box-beam bridges, which are to receive an asphalt wearing surface. POLY-CARB Inc., a Dow Chemical business that manufactures bridge deck overlays, protective coatings and linings, has been working closely with KTU Constructors on the project.
POLY-CARB’s MARK-155 UREGRID Waterproofing System was chosen for application to all 215 bridges—a total of 686,540 square feet. The polymer monolithic waterproofing system is designed for conventional and reinforced concrete, box-beam and metal bridge decks that have an asphalt wearing surface.
The material is being spray-applied with robotic technology specially developed for the Safe & Sound application. The product is designed to cure quickly and provide long-term protection from corrosion caused by water, de-icing chemicals and other contaminants.
MoDOT keeps the public well apprised of the projects’ progress, closings and reopenings, with a website that includes an interactive map, project schedules, time-lapse videos of projects, and other updated information.
“We promised to give Missourians a safer transportation system by fixing hundreds of our lowest-rated bridges in a short amount of time, and we’ll deliver on our promise,” then-MoDOT director Pete Rahn said at the project’s kickoff.
“We are excited to get to work. The sooner these bridges are under construction, the sooner Missourians will reap the benefits: safer roads, more jobs and increased mobility.”