After a stormy Atlantic night in February 1998, the people of Hall’s Harbour in Nova Scotia awoke to find the mid-section of their breakwater/wharf collapsed. In seeking a feasible solution they were drawn to trying new technologies, and now lay claim to Canada’s first marine structure utilizing lightweight, non-corroding glass fibre reinforced polymers (GFRPs) and a steel-free deck.
The small community of Hall’s Harbour has the only safe harbour on the Fundy Shore north of Digby which is open throughout the winter months. With the failure of a 40-m section of wharf timber piles, the need to rehabilitate the 1904 structure took on the highest level of urgency. Like many East Coast communities, Hall’s Harbour had recently assumed responsibility for its marine infrastructure from the federal government. Now, the relatively new Harbour Authority of Hall’s Harbour was in a critical situation – nominal funding and its first infrastructure failure.
In preliminary design work with Vaughan Engineering, ISIS Canada’s team in Halifax has shown that the cost of the innovative materials and technologies is only slightly more than that associated with conventional methods. The additional cost of the GFRP reinforcements and stee-free deck over conventional steel reinforced concrete is $20,000, or 4.5 percent more.
The long-term benefits, however, are substantially more attractive because the absence of steel reinforcements extends the life of the wharf from approximately 30 years to between 60 to 80 years with minimal maintenance – critical factors given that communities like Hall’s Harbour are solely responsible for maintaining their wharves. The inclusion of fibre optic monitoring technology embedded in glass rods (a newly patented Canadian technology) will add solid data to support the application of the fibre reinforced polymers in other marine environment structures.
The wharf incorporates five innovative technologies. The new structure will be constructed with concrete deck panels on deep concrete beams spaced at approximately 4-m intervals. The transverse beams will be supported on piles at the front face and a retaining at the back. The piles will be a steel-free concrete core encased in a GFRP jacket. The GFRP jacket will provide the reinforcement against bending as well as the circumferential confinement necessary for adequate performance. The pile caps and bents will contain some steel reinforcement; however, reinforcement under low service stresses will be GFRP rods. The deck panels will contain synthetic fibre reinforced concrete and utilize an internal compressive arching technology. The panels will also contain GFRP rods to reinforce against uplift force created by wave action during extreme storm events. In all elements, high performance concrete donated by St. Lawrence Cement is being used.
The Fundy Shore is known for its large tidal range. In Hall’s Harbour the average daily tidal range is 10-m. Therefore, the entire structure is in the critical tidal zone where corrosion is most likely to occur. As well, the entire wharf is subject to daily wet freeze-thaw cycles. Combined with severe Atlantic storms, Hall’s Harbour makes an ideal site for demonstrating the durability of lightweight FRPs.