Benjamin Oltmann, P.E., served as the bridge design team leader on the Wolf Trap pedestrian bridge project completed in Vienna, Va., in April 2012. The Federal Highway Administration (FHWA) required accelerated construction of the bridge – which crosses over a 10-lane highway – to reduce lane closures. The FHWA selected FRP bridge decks, in part, because they could be installed much faster than concrete ones. Composite Advantage in Dayton, Ohio, supplied the FRP bridge decks. A case study of the project appears in the January/February issue of Composites Manufacturing magazine. Here, Oltmann provides additional information about the project and the FHWA’s use of composites.
Why did the FHWA design the Wolf Trap pedestrian bridge with a FRP bridge deck rather than a timber deck or concrete one?
The FRP deck was selected due to its light weight. Our engineers wanted the deck to be installed on the trusses prior to erection to minimize work over Route 267 and reduce traffic control impacts to Route 267, such as closed lanes during construction, delays, etc.
What advantages do FRP bridge decks offer over ones made from traditional materials?
We selected the FRP deck due to its light weight. The non-skid wearing surface was also very nice, although it is similar to the concrete deck.
What are its disadvantages?
The panels came in 10- to 12-foot lengths. This created a transverse joint every 10 or 12 feet, which our engineers sealed with silicon joint sealant. Because these joints will have to be maintained more often, we expect a slight increase in maintenance costs over the structure’s life.
Composites are often more expensive than traditional materials. Can you provide examples of situations where higher material costs are justified?
On this project, the higher cost of composites was justified as the deck work could be completed off site prior to erection. There were real savings in the elimination of traffic control that would have been required to install a traditional concrete deck over the heavily trafficked roadway below the pedestrian bridge. Since the panels were prefabricated off site, this shortened construction time and allowed for work to be completed concurrently at the site and back at the deck-panel fabrication facility. It also increased worker safety because the less the workers are exposed to working near traffic, the less risk there is for accidents and fatalities for workers and drivers alike.