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Scotia Plaza, Toronto

Planned over a number of years, the final design for Scotia Plaza that evolved was a 70storey, 275 meter high tower costing over $200 M with structural costs of under $200 per sq.m. 
The structure incorporated advanced features of design and construction including: ➢ A tube-within-a-tube structure ➢ Unique concrete/structural steel combination ➢ Ultra high-strength concrete of 70 MPa using silica  fume ➢ Self-climbing formwork for  vertical elements ➢ The use of self-elevating concrete forms, for all vertical components ➢ The transportation of concrete by pumping, from a site across the street, a distance of 70 metres, to a maximum height of 275 metres ➢ The investigation and restraint of lateral rock relief movement in deep foundations  ➢ The use of liquid nitrogen as a cooling agent for high strength concrete
Earlier schemes envisaged a 64-storey all-steel tower (64 storey single tower).  Quinn Dressel Associates concluded that a perimeter tube in conjunction with the core provided better lateral resistance for the structure, and convinced the Owner and the Architect that it offered more flexibility and potential to make the building taller.  The final 70-storey configuration was adopted. 
The benefits of high-strength concrete for lateral stiffness and increased vertical load-carrying capacity in conjunction with the lightness and long-span capabilities of structural steel for horizontal elements provided a unique solution.  Typical floors were constructed in a 3-day cycle and the structure as designed was topped off at the end of 1987.  The 5 level basement includes 3 levels of parking for over 700 cars.  
The decision to employ the Concrete Tube and Concrete Core with Steel Framed Floors meant introducing into Canada the high technology of self-elevating forms for the vertical components of the structure, and was a world first in two such operations on the same project.  With the selection of the structural system, the maximum concrete strengths were set at 70 MPa which satisfied all structural and architectural requirements.

Photo Courtesy of Steven Evans Photography & WZMH