Keeping things moving with FRP

 

Over the past year, composite materials have received increased consideration for infrastructure projects. New legislative efforts such as the IMAGINE Act (Innovative Materials in American Grid and Infrastructure Newly Expanded) are helping to increase awareness of the potential life cycle cost savings composite materials can provide for infrastructure projects. New bridge projects continue to provide examples of how composites and advanced materials can help rebuild crumbling infrastructure and build new lightweight corrosion-resistant, sustainable structures that can stand the test of time and the elements. Two recent projects using fiber-reinforced polymer (FRP) bridge decking material from  Composite Advantage (Dayton, Ohio, U.S.) demonstrate the role composites can play in repairing and building bridges.

Buckled bridge repair

In February 2019, record-breaking temperatures buckled Michigan City, Indiana’s Franklin Street Bridge. The 87-year-old structure — the lakeshore town’s only movable [bascule] bridge — crosses Trail Creek, a gateway to Lake Michigan for locals and tourists. The structure uses counterweights to raise and lower its spans to provide clearance for boat traffic. Its’ crumbling concrete “leaves” and steel supports needed a quick fix. The LaPorte County Highway Department’s contractors and engineers found a lightweight, corrosion-resistant alternative with Composite Advantage’s fiber-reinforced polymer (FRP) FiberSPAN system. 

“The traditional approach called for a temporary steel plate until the weather warmed up enough to accommodate the 28-day cure requirement for concrete,” says Scott Reeve, president of Composite Advantage. “But that would have taken months. It also meant paying for two repairs and closing the bridge to traffic twice. The need for light weight eliminated most material options. But the accelerated construction value of our prefabricated FRP panels sealed the decision.”

The project called for two spans [or leaves] 15 feet wide, 35 feet long and seven inches thick. Performance requirements included a 30 psf live load, a vehicle load of HL-93, a deflection rating of L/500 and a deck of 23.5 psf.

“Prefab decking that drops in place is especially beneficial for these types of projects,” Reeve says. “The flexibility of FRP allowed us to perform design, coordination and review tasks in hours instead of days and without the customary long lag times that you usually have with these jobs.”

Composite Advantage prefabricated the panels with mechanical clips for bolting the deck to the steel stringers. A black nonslip overlay of aluminum oxide aggregate was used on the surface. The FRP supplier was able to design, prefabricate, ship and install the panels in just 32 days. Franklin Street Bridge re-opened to commuters and visitors in April 2019.

Pedestrian bridge provides much-needed shortcut

 

Chelsea is Massachusetts’ smallest city with a land area of just 1.8 square miles yet the Suffolk, County town is the United States’ 26^th most densely populated community.  Overcrowded downtown transit stations prompted the Massachusetts Bay Transportation Authority (MBTA) to open Bellingham Square Station in 2018.  But the hills and elevations between junctions meant commuters had to walk more than three blocks to navigate between Main Street and the train station. A FiberSPAN three-level-switchback ramp provided an Americans With Disabilities (ADA)-compliant direct pathway that made commuter time safer, shorter and more convenient.

“The Massachusetts Bay Transportation Authority needed a wheelchair accessible ramp,” says Reeve. “Traditionally switchback ramps are constructed with reinforced concrete. But spatial constraints and complex design requirements made the use of concrete prohibitive in terms of material and labor costs. Switchback ramps reduce the overall footprint of a ramp significantly. Fiber-reinforced polymer (FRP) is lightweight and quick to install eliminating issues with traffic disruption and the need for extra manpower and machinery needed to lift and position heavy concrete ramps.”

Almost 90% lighter than concrete, FRP bridge deck panels were prefabricated in sections up to 22 feet long by 8 feet wide and 5 inches deep. The project called for a deck weight of 9 psf and a 90 psf live load with a deflection rating of L/360.  Beam spacing on a concrete beam superstructure required spacing up to 20 ft. with a deck-to-beam connection using angle brackets. Custom requirements included switchback ramps, ramp landing panels with multiple slopes to drainage scuppers, a non-slip overlay using blue-gray quartz aggregate, and a guard rail that attached to integral curbs. The FRP switchback pedestrian bridge with a total deck area of 2,092 square feet, was installed in January 2018.