The Queen Richmond Centre West is an iconic development in Toronto that is a model of urban intensification, featuring the modernization of two historic buildings together with the construction of a new 11-storey office tower.

In 2010, Allied Properties REIT commissioned Sweeny &Co Architects (&Co) to design a landmark mixed-use development in Toronto’s entertainment district.  Given the positioning of the two existing heritage structures on the site, &Co engaged Stephenson Engineering and presented the structural engineering firm with the challenge of suspending an office building above the two existing structures.  This configuration would form a large L-shaped, glass-enclosed atrium with direct access from streets to the east and south of the complex as well as to a mid-block public lane to the north.  &Co’s desire to offer office space with clean, unobstructed ceilings drove their selection to an exposed reinforced concrete structural system for the 11-story tower.

Stephenson Engineering developed a solution which called for the creation of a “tabletop” platform seven stories in the air from which the office building could be constructed. The tabletop’s supporting structure was a significant challenge considering the enormous loads involved, the need for lateral stiffness given the eccentric location of the elevator core, the more than 75-ft unbraced height from the top of the foundation level to the underside of the tabletop, and the architectural desire to support the building above with a structure that wouldn’t clutter the atrium.

Stephenson Engineering led a design charrette with &Co which resulted in the design of the “Mega Delta-Frame” system that was ultimately employed in the design and construction of the building.

Each of the three frames is an hourglass space frame configuration formed from two stacked rectangular-based space frame pyramids – the top pyramid being inverted such that the apex of both pyramids meet at one central node 40-feet in the air.

Mega Delta-Frames also form a major part of the lateral system – the only other effectual lateral support through the atrium space is provided by reinforced concrete stairs and an elevator core.  Each Mega Delta-Frame is capable of supporting forces of 80,000kN, which is approximately equivalent to the weight of 400 transport trucks.

Each frame is comprised of 1-metre diameter steel legs with a steal thickness of 2-inchs, pressure-filled concrete and a 17-ton cast steel nodes engineered by CAST CONNEX. The result is a soaring open air atrium that sets the development apart from any other.