Dayton, Ohio — In 2017, the City of London, Ontario launched a $7.9 million project to remove, dismantle and rehabilitate Blackfriars Bridge. The 143-year-old wrought iron bowstring arch-truss structure, which connects Ridout and Blackfriars streets, is Ontario’s oldest working crossing. The 221-foot, 1/2-inch-long bridge deck carries vehicles, cyclists and foot traffic across the north branch of the Thames River. Concrete combined with current traffic loads proved too heavy for the historic structure. London-based Dillon Consulting and the City of London selected Composite Advantage’s fiber reinforced polymer (FRP) FiberSPAN deck following research and study of the product’s performance on two Ottawa vehicle bridges.
“FRP panels are 80 percent lighter than reinforced concrete panels,” says Composite Advantage President Scott Reeve. “The goal was to preserve as many of the original components as possible such as the structure’s arches, lattice work and pedestrian railing. The design flexibility of FRP allowed us to mesh advanced composite material with Blackfriar’s original components to retain the beauty of the architecture while giving it long-lasting performance.”
Design requirements included a design vehicle loading of 75 percent of CL3-625-ONT with a 1.3 dynamic load allowance and a 0.9 environmental durability factor. Allowable stress design (ASD) standards and limit states design (LSD) determined safety factors which were compared to design strain requirements. Traditional beam bending equations were used to analyze FiberSPAN deck panels constructed as a series of closely spaced I-beams. Panels met an L/500 deflection. Bending strain/shear strain was less than 20 percent under the service load plus dead load. Minimum fatigue life was rated at 2 million cycles. Panels were designed to a temperature differential of 60 Celsius. The design allows the bridge deck to move independently of steel beams in the longitudinal direction.
The 221.5-foot-long FRP deck was installed on Blackfriars’ rehabilitated steel truss. Direct bolting of the 17.5-foot-wide panels was designed to handle braking loads while connection clips resist uplift and lateral movement of the bridge. Panel widths ranged from 7 inches to 9 inches thick with a molded in crown. Curbs, integrally molded into the FRP deck, were covered with 3/8-inch-thick 304 stainless steel plates to protect from wheel impacts and snow plows. The FRP deck was given a dark aluminum oxide wear surface. The large prefabricated FRP panels eliminate the labor and hours associated with assembling multiple pieces or pouring concrete.
“Blackfriars Bridge is a key corridor into our downtown and a link to our local cycling network,” says Doug MacRae, Director of Roads and Transportation, City of London. “We selected FRP decking for the Blackfriars Bridge rehabilitation project for its durability and corrosion-resistant qualities. We wanted a material that would reduce the amount of maintenance work needed once the bridge was reopened to pedestrians, cyclists and motorists.”