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Lethbridge Viaduct

From Academic Kids

Lethbridge Viaduct - A. Rafton / National Archives of Canada / PA-029691
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Lethbridge Viaduct - A. Rafton / National Archives of Canada / PA-029691

The Lethbridge Viaduct better known as the High Level Bridge was constructed between 19071909 at Lethbridge, Alberta, Canada at a cost of $1,334,525.

This massive viaduct over the Oldman River was designed by the Canadian Pacific Railway's bridge department in Montreal. The field work was directed by CPR's Assistant Chief Engineer J. E. Schwitzer. The steel work was manufactured by the Canadian Bridge Company of Walkerville, Ontario. A 100 man gang worked on the erection of the steel. Although there were some initial problems with settlement the bridge has proved to be an enduring engineering work. The bridge is still in use.

This bridge is one of the largest railway structures in Canada. It was built as part of a major diversion of the Crowsnest Pass route between Lethbridge and Fort Macleod. The river crossing was previously over a wooden trestle measuring 2,933 feet (894 m) long and 65 feet (20 m) high. That original wooden structure was impressive in its own right.

That old approach was over steep grades that hampered operations. In addition, extensive cuts, many other bridges were also needed to cross various creeks and coulees. Past the St Mary's River crossing several large cuts had been required. Large bridges were also required, including a 900-foot (275-m) trestle with a 200-foot (61-m) span west of the St. Mary's River, a 600-foot (183-m) trestle at Eight-Mile Coulee and another of 900 feet (274-m) in length near Eight-Mile Coulee. At Sixteen-Mile Coulee there was an 800-foot (244-m) trestle, 133 feet (40.5-m) high with a 200-foot (61-m) truss span over the creek. The trestles on the original line out of Lethbridge totalled 2.8 miles (4.5 km). Although the original route accomplished its purpose in allowing the CPR to rapidly complete the railway, it turned out to be expensive to operate. The original bridges were designed to last only about 10 years. The CPR decided, in 1905 to construct a completely new route on a better gradient to bypass the original line. The new line was built to the north of the Oldman River. It required two bridges, one just west of Lethbridge - this famous High Level Bridge - over the Oldman River and another large bridge over the Oldman River again west of Monarch. This route eliminated many curves and reduced the grade from 1.2 percent to only 0.4 percent. It also saved 5.26 miles (8.5 km) of track.

Construction began in the summer of 1907. Clearing and grading the site, the construction of piers, and placement of the footings progressed while the steel work was being prefabricated. Raising the steel work began in mid-August 1908. Once the steel work reached track level at the Lethbridge end, it was possible to begin using a huge travelling crane, pictured below, called an "erection traveller". It was used to lower the steel beams and girders into place. The last girder was placed in June 1909 and riveting was completed in August 1909. Transport the steel to the site required 645 railway cars while another 40 were needed to bring in equipment.

Specifications

Image:Lethbridge Viaduct Crane.jpg
  • Length: 5,327.625 feet (1,623.86 m)
  • Height: 314 feet (95.7 m) above river bed
  • Materials: 12,400 tons of steel
  • Deck Spans and lengths:
    • 44 plate girder spans each of 67 feet, 1 inch (20.4 m)
    • 22 plate girder spans each of 98 feet, 10 inches (30.15 m)
    • one riveted lattice-truss of 107 feet (32.6 m)
  • Rigid braced steel towers: total of 33

The second bridge, over the Oldman River, is 1,890 feet (576 m) long and 150 feet (45.7 m) high.

External link

See also: List of bridges

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