A crumbling, rusting heavy-vehicle bridge in Washington, D.C., made of reinforced concrete and steel rebar has been replaced with one with a fiberglass-reinforced composite deck.
The 29th Street Bridge spans the stone walls of the historic Chesapeake and Ohio (C&O) Canal that runs throughout Washington's Georgetown district. To help reduce the load on the old walls, officials at the D.C. Department of Transportation wanted a replacement bridge deck that would weigh less than concrete and steel.
Click the image below to see the new bridge and how it was built.
The original 29th Street vehicle bridge in Washington, D.C., which spanned the stone walls of the historic Chesapeake and Ohio (C&O) Canal that runs throughout the city's Georgetown district. (Source: Composite Advantage)
The fiberglass-reinforced polymer vehicle bridge deck is constructed with molded panels made of Composite Advantage's FiberSPAN material. The company says on its website that each panel is a sandwich containing internal grids of bi-directional shear webs for the distribution of heavy truck loads. They weigh about one-fifth as much as concrete.
Composite Advantage makes large fiber-reinforced composite components of up to 52 feet long for vehicle and pedestrian bridges, rail station platforms, and waterfront infrastructure such as pier components. For the 29th Street Bridge, it installed five deck panels on a substructure made of steel beams. Shear studs were welded to the beams, and the panels were bolted to those studs. An asphalt wear surface was applied on top of the bridge deck. A fiberglass-reinforced composite sidewalk was bonded to one side of the bridge, and granite curbs were attached to the edges of the bridge deck.
The new short-span vehicle bridge -- the area's first with a deck made of this material -- is 39 feet long by 32 feet wide. Its structure, combined with its lighter weight, helps support the stone walls of the C&O canal and keep them upright.
Watashi, I think you're right that only time will tell about the maintenance costs, how those affect cost-of-ownership/lifecycle costs, and how long the bridges made of this stuff will last. Or, for that matter, the pontoons, docks and other structures made of carbon composites. OTOH, it's good to remember that this material is now being used on spacecraft going to Jupiter, space is an extremely hostile environment, and there aren't any repair robots onboard.
However, they may have a good story as far as whole lifecycle cost if their products can last longer with much less maintenance. But only time will tell. Structural plastics in this application are too new to realy know for sure.
Doc K, you'd have to ask the company for customer data. In my experience, manufacturers aren't very forthcoming with that type of info. In addition, because it's plastics, cost comparisons vary widely, being highly dependent on a specific implementation.
Chuck, thanks for the clarification and for pointing out the different sub- and super-structure meanings. As I understood it, the only composites are in the bridge deck and sidewalk. I used the term "substructure" as shorthand to mean everything underneath.
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