FiberSPAN Bridge Deck Right Solution For Rare, 143-Year-Old Bowstring Arch Truss Span in London, Ontario Canada
When London, Ontario launched a $7.9 million project to remove, dismantle and rebuild the community’s beloved Blackfriars Bridge, the city needed a lightweight deck solution. The 143-year-old structure is a rare example of wrought iron bowstring arch-truss architecture. Blackfriars is Ontario’s oldest working crossing and at 216 ft., North America’s longest working span of its kind. It was designated as a National Historic Civil Engineering Site by the Canadian Society for Civil Engineering in 1992. In 2013 the bridge was closed to vehicular traffic while the city inspected and evaluated its condition and performance. Use was restricted to pedestrians and cyclists following temporary repairs. Extensive restoration work began in November 2017 when the bridge was lifted from its granite abutments, cut at mid-span and taken to the banks of the Thames River. The challenge? To mesh a fiber reinforced polymer (FRP) bridge deck with original components to retain Blackfriars’ beauty while giving it long-lasting performance.
FRP Anti-Aging Solution
Crews spent the winter rehabilitating and strengthening the truss structural sections of Blackfriars Bridge at contractor McLean-Taylor Construction’s yard north of London. The goal was to preserve as many of the original components as possible such as the structure’s arches, lattice work and pedestrian railing. Extensive bicycle and walking paths framed by second growth trees also motivated city officials to use an approach that would preserve and restore the bridge’s bowstring arch-truss structure which gives it the appearance of floating. FRP was chosen for the deck because the historic bridge could not tolerate the dead load of a concrete deck combined with current traffic loads. Dillon Consulting [based in London, Ontario] selected Composite Advantage’s FiberSPAN lightweight decking after studying two other FiberSPAN bridge decks on vehicle bridges in Ottawa.
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 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 2,000,000 cycles. Panels were designed to a temperature differential of 60 Centigrade. Maximum bending moment was based on a moment diagram developed for a worst case loading configuration of 75 percent truck loading with a 1.3 impact factor. The design allows the bridge deck to move independently of steel beams in the longitudinal direction.
FRP bridge panels waiting in Composite Advantage's shipping yard to be transported to the Blackfriars Bridge.
The FRP deck was installed on Blackfriars’ rehabilitated steel truss. Direct bolting of panels was designed to handle braking loads while the connection clips resist uplift and lateral movement of the bridge. Connection clips were bolted into an embedded 3/8 in. thick 304 stainless steel plate inside the FRP panel. Integrally molded into the FRP deck, curbs were covered with 3/8 in. 304 stainless steel plates to protect from wheel impacts. 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.
Installation of the FRP bridge panels