While most cables were tensioned from below using hydraulic jacks, some had to be tensioned from the top of the building, resulting in scheduling conflicts. The cables had to be protected from moisture and tensioning operations were scheduled around slipform work. The cables were fed downward through ducts by a hand-controlled reel system to the tower foundation. Only when the tower reached 300 feet did the city issue a building permit.Īn article written by CN Tower engineers appeared in a 1976 issue of the Precast Concrete Institute Journal and describes the difficulty of engineering the post-stressed tensioning cables that helped to strengthen the tower. Lansdale notes the concrete was hand poured using wheelbarrows around the periphery of the structure.Ī single crane rode slowly up the concrete tower as it ascended. Concrete in the tower was single-sourced and mixed on site to ensure uniform consistency. As each layer of concrete cured around rebar, the slipform was raised and adjusted according to the design contours. The foundation was completed in May.Ĭoncrete pouring on the tower began in June using a sophisticated slipform supported by a series of hydraulic-powered climbing jacks. The foundation comprised 7,046 cubic metres of concrete and 453 tonnes of reinforcing steel. Foundation work began in March on a concrete-and-steel foundation 6.71 metres deep. Excavation of the foundation to bedrock began in February 1973 as crews removed more than 56,000 tonnes of earth and shale. Other milestones followed in rapid succession. 8, 1972 with demolition and clearing of existing railroad infrastructure-and no building permit. ROBERT TAYLOR/WIKIMEDIA COMMONS - Main Pod of CN Tower under construction.Ĭonstruction began on Dec. Lansdale notes that the initial pitch for the CN Tower imagined a budget of $12 million, a significant underestimation. “I have been working on the CN Tower project for decades and expect to finish it in 30 years’ time,” he says. His current labour of love is a complete frame-by-frame restoration of the last known pristine copy of a 16mm film on construction of the CN Tower produced by Canron. Lansdale continues to chronicle every aspect of construction, including the names of individuals who worked on the project and personal interviews with them. The most detailed history of CN Tower construction has been researched by Robert Lansdale, historian and curator at. and excavation contractor Rumble Contracting Inc. Major contributors to the project team included: NCK Engineering (structural engineer) John Andrews Architects architects of record, the Webb, Zerafa, Menkes, Housden Partnership (now WZMH Architects) The Foundation Company of Canada (now part of AECON) steel fabricator Canron (Eastern Structural Division) Scanada Slipform Systems Inc. However, part of the reason for the project was a simple act of will, demonstrating to the world what Canadian architects, builders, engineers and corporate clout could achieve. At a little over 1,815 feet, the tower could beam signals of all sorts to Canadian markets and across Lake Ontario to the United States. There was a solid reason for building the tower-radio and television signals were no longer reaching the city unimpeded, thanks to rapid highrise expansion. Ultimately, it was the only feature of the Metro Centre development that was realized. The CN Tower was conceived as only one feature of a complete redevelopment of the Railway Lands owned and maintained by the Canadian National Railway. The city has seen major construction projects before and since, but not one so visible that almost every citizen could mark its stunning progress as it rose from the city’s downtown. More than 40 years after its grand opening, the CN Tower remains remarkably relevant: an engineering marvel, a major attraction and an irreplaceable part of the Toronto skyline.
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