As more people walk or ride bikes in congested cities, cities with bridges are finding it difficult to handle continued increases in usage. A Canadian company has devised lightweight bridge extensions that can be added to existing structures.
The Maadi Group of Montreal, Quebec designed modular components that can be constructed fairly quickly. Since the elements are made with extruded aluminum, finished structures are lightweight, so they can be added to many structures without exceeding weight limits.
The system can also be used to link upper floors of adjacent skyscrapers as well as adding walkways in large interior spaces like shopping malls. The bridges come in two formats. One is for short spans, like dockside gangways and small bridges in parks or golf courses. The other is for longer pedestrian bridges. The latter recently received approval from the American Association of State Highway and Transportation Officials (AASHTO) and the Canadian Standards Association.
Since the bridges will often be attached to structures that are already in use, construction must be simple and fairly quick. At the same time, reliability and safety are key issues.
“We’ve got a cast aluminum hub and we insert extruded members into it. They’re held in place with only one bolt. That bolt is not accessible once the bridge is finished, so it can’t be sabotaged," says Alex de la Chevrotiere, aluminum structures engineer at Maadi.
That ease of use extends to getting the components to the worksite. Since the components are mainly straight pieces of aluminum, loading them onto trucks is fairly straightforward. “You can fit 600 feet of bridges on one semi," de la Chevrotiere says.
Though the aluminum bridges are far lighter than comparable steel installations, durability shouldn’t be an issue. “The parts are not welded so they are as strong as A-36 steel," de la Chevrotiere says.
The modular bridge system is being highlighted at ET ’08, an aluminum extrusion technology show in Orlando. It won a prize for innovation at the show, held every four years.