Scotia Plaza Toronto, Ontario
Scotia Plaza is a 69 storey, 275m high tower with a total area of 223,000 sq.m., a construction cost in excess of $200,000,000 and a structural cost of under $215.00 per sq.m.
Its structural component advanced Canadian design and construction technology by:
- Its unique structural system, incorporating the best of concrete and structural steel qualities.
- The use of ultra high strength concrete.
- The use of silica fume concrete.
- 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.
- 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.
The planning was an intensive process which extended over a number of years. One of the earlier schemes called for the demolition of the existing Bank of Nova Scotia Building and the building of a 64 storey tower in its place on the corner of this major intersection. Potential political delay, the cost of demolition, the pressure to maintain the existing Bank of Nova Scotia vaults in continuous operation and the square foot bonus for retention precluded this scheme.
With the acceptance that the new tower would be located in the confined space east of the existing Bank of Nova Scotia Building, the design team produced a 64 storey tower. The structural engineers concluded from studies, that while an outrigged arrangement would be practical but at its limit as the wind resisting system, a perimeter tube structure should be considered because it offered more flexibility in layout and the potential for extra floors. The architectural team decided to integrate a tube expression in the architectural solution.
Subsequently, a higher density was permitted and the tower increased in height to its final 69 storey configuration. The investigation narrowed to five basic structural systems, namely:
Scheme 1: All Concrete
Scheme 2: Concrete Tube/Concrete Core/Steel Framed Floor
Scheme 3: Steel Tube/Concrete Core/Steel Framed Floor
Scheme 4: All Steel
Scheme 5: Concrete Tube/Steel Core/Steel Framed Floor
In proposing the concrete schemes it was recognized that concrete strengths of 75 MPa would be required for practical column sizes. Strengths in the range of 85 MPa to 90 MPa were also considered but not pursued as they were too far beyond the current state of the art in Toronto. Maximum concrete strengths in the Toronto area were 55 MPa, and the industry was surveyed to ascertain their willingness and technical competence to produce such a high strength. The response was positive from both a technical and cost point of view and design continued using the higher strength concretes. Costs were estimated for the five basic schemes and the lowest in order were:
Scheme 1: All Concrete
Scheme 2: Concrete Tube/Concrete Core/Steel Framed Floor
Scheme 5: Concrete Tube/Steel Core/Steel Framed Floor
Preliminary schedules showed small differences in costs and construction times, and the final selection of Scheme 2 at under $200.00/sq.m. was based on owner and architect preferences. In construction, typical floors did achieve the predicated 3 day cycle.
The decision to employ the Concrete Tube and Concrete Core with Steel Framed Flores, 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. After the award for the supply of concrete, an extensive testing and trial batching program was undertaken and the concrete supplier elected to proceed with silica fume mixes of his initial 100% slag based mix designs. The structure was constructed as designed and topped off at the end of 1987.
The benefits of high-technology concrete with its cost advantages in lateral stiffness and vertical load-carrying capacity, in conjunction with the lightness and spanning abilities of structural steel, provided a unique solution.
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