Canada spearheads approach in bridge reinforcement
During March and April experts who helped to develop some of the groundbreaking provisions in the CSA-CSCE Canadian...
During March and April experts who helped to develop some of the groundbreaking provisions in the CSA-CSCE Canadian Highway Bridge Design Code visited cities across Canada. At the seminar in Toronto on April 10, about 80 civil engineers were in a downtown Toronto hotel opposite the old Maple Leaf Gardens to hear presentations on important new provisions in the code’s 2006 edition.
Baider Bakht, Ph.D., of JMBT Structures Research of Toronto who was vice-chair of the technical committee on the new code, spoke of one of the most important provisions in Section 16. These now allow the use of fibre reinforced polymer, or “FRP” reinforcing to be used in both new and rehabilitated bridges and structures made of concrete or wood. The previous edition of the code from 2000 had allowed FRPs to be used in new construction only.
The Canadian bridge code is the only one in the world to permit this use of these composite reinforcing materials. This makes it, according to the publisher, Canadian Standards Association, and the Canadian Society for Civil Engineering, “the leading code for bridge design by engineers around the world.”
The code allows fibre reinforced polymer reinforcing for concrete bridges so long as the structure is not permanently submerged in water. This decision was made, Bakht explained, after cores taken from several bridges reinforced with FRP were thoroughly tested and it was found that they had no evidence of degradation or delamination. Sample cores were taken, for example, from the Joffre Bridge in Quebec and the Crowchild Bridge in Calgary.
Bakht explained the mechanics of the composite reinforcing, how the fibres provide mechanical strength and the resins provide chemical resistance. Common fibres used are aramid, carbon and glass, while resins can be thermoset or thermoplastic. Thermoset resins cannot be bended or moulded after they have been cured. Thermoplastic resins soften to viscous liquids when heated and require approval. Because of the complexity of FRPs, Bakht suggested that civil engineers do need to call on material experts when using them. He also suggested that designers need to provide alternate load paths for their structures when using FRPs.
Fibre reinforced polymer materials have been used in the aeronautical industry for decades. They are seen as a promising alternative to steel reinforcing for civil structures because they are lightweight, strong and don’t suffer from corrosion with contact with road salts.
Bakht said that he and other Canadians exploring the use of FRPs in construction first saw the technology used in laboratory tests in Switzerland and Germany in the late 1980s. The first bridge constructed using FRPs was the Ullenbergstrasse in Germany in 1986. The high costs of the technology have, however, prevented it becoming used on a wide scale. Canada’s first bridge reinforced with FRP tendons was the Beddington Street Bridge in Calgary built in 1993.
The seminars on the new bridge design code were organized by the Canadian Society for Civil Engineering and the Canadian Standards Association and held in Vancouver, Calgary, Edmonton, Moncton, St. John’s, Ottawa, Ontario, Montreal, and Quebec City.