Trestle Cove: Two New Aluminum Footbridges Take Their Place in History

November 18, 2019

Custom pedestrian bridge over lake in Quebec Canada

November 18, 2019—Brome Lake, Quebec, Canada—In the days of the railroad when travel by train meant limitless adventure, Canadian Pacific built a line from the watering station at Foster into the U.S. Passing along Brome Lake, Quebec, south east of Montreal, a 656 ft (200 m) long wooden trestle bridge was built over a bay to avoid having a tight bend in the railroad. The ice destroyed it so the company built an island embankment with a short trestle at each end to cross the bay. Canadian Pacific shut down this rail line in the 1960s and demolished both bridges in the early 1980s. The Town of Brome Lake received the railroad bed, which became a popular path for walking and cycling, but the missing bridges limited its appeal and usefulness.

After close to 20 years debating the construction of two bridges, last March, the municipality awarded a contract for $874,655 (plus taxes) to BSL, general contractor, to build and install bridges in the Trestle Cove area. They hired MAADI Group Inc., the Quebec-based aluminum bridge manufacturer to design and construct them.

“MAADI Group engineers lightweight bridges and they’re pros,” said Neil McCubbin, a retired engineer who was part of the local group of residents researching to find a way to realise the project.

“Foremost in our minds was the security of the bridges’ users,” said MAADI Group CEO Alexandre de la Chevrotière, IWE, P. Eng., whose company focuses on innovation in manufacturing aluminum pedestrian bridges, marine structures and other distinctive engineering products, and has built and installed hundreds of bridges in Canada and abroad. “Now people can enjoy the stunning scenery using a bike, on foot, with a golf cart or a wheelchair. The bridges are safe and accessible to all.”

The aluminum trestle bridges comply to the most rigorous standards, such as the Canadian bridge code CSA S6-14 (2014) and Canadian strength design in aluminum code CSA S157-05 (R2010). As per the bridge code, distributed live load is 77 psf (3.67 kPa) for a span of 130 ft (40 m); concentrated load is 0.4 kips (1.6 kN) over a rectangular area 3.28 ft x 1.64 ft (1.00 m x 0.50 m) while horizontal safety rail uniform load is 0.9 kips/ft (1.20 kN/m) applied laterally and vertically simultaneously and wind pressure is 8.4 psf (400 Pa) for a return period of 50 years.

Experienced certified aluminum welders carried out the welding for the two bridges according to CSA W47.2-11 (division 1) and CSA W59.2-18 standards. Aluminum parts were joined on site using GMAW welding techniques with welding procedure specification (WPS) using aluminum alloy 6061 and filler 5356 for bridge structures. The high grip floor is made from extruded 6005A-T6 aluminum transversal planks coated with an anti-skid durable polyester powder coating finish, Sandtex appearance, 3±2 units on 60° gloss, compliant to standards AAMA 2604-10 & ASTM D3359. The horizontal safety rails and kickplates are clear anodized standard AA-M12C22A41 class 1, 0.28 inch (0.7 mm) thickness and, with the floor system, are fixed with 304 stainless steel rivets.

De la Chevrotière said that getting the bridges in place wasn’t exactly a walk in the park.

The site is remote and difficult to access with heavy equipment, which made crane lifting out of the question. The helicopter lifting capacity is limited to 10,000 lb (4,536 kg), and a full 131 ft (40 m) bridge with decking, railings and hardware weighs 24,000 lb (10,886 kg), so both bridges had to be sectioned into two to facilitate transportation.

The bridges are supported on helical piles at each end. The sections are fixed, on supports and bridge splice, with 300 series stainless steel 1.25-inch (31.75-mm) diameter heavy fasteners. The bridge’s mobile anchors allow up to 5.9 inches (150 mm) of thermal expansion and the quality management system as per ISO 9001:2015. Fitting these bridges into place—each one on either side of the finger-shaped island—was a challenge that was executed successfully in one day.

The two 130 ft (40 m) Warren pony truss bridges tower above the water at a height of more than 16 ft (5.5 m). Both structures measure 71 inches (1.8 m) of clear width and 51 inches (1.38 m) of clear height and are part of Quilliams Trail system. McCubbin noted that the new aluminum structures will allow locals and visitors to cycle from the village of Knowlton northwards to the 3,106.86 miles (5,000 km) Route Verte bicycle trail network that is free of motor vehicle traffic, and take advantage of the panoramic views of the lake and surrounding woodlands. The new bridges also open up several local loops for off-highway cycling and walking.

It’s a known fact that many people come to Brome Lake to get away from it all. An editorial in Tempo, the local newspaper from June 2015, remarks that the trails are a draw to visitors who will then eat and shop, bolstering the local economy. The editorial also noted that the bridges represent a “critical piece of the puzzle” as they connect up trails and become part of a larger trail system.

Following the same route as people who traveled by train in the late 1800s, today’s travelers—whether from far away or close by—can now share in a piece of history while enjoying a closer view of the lake and living an active life.

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