THE ATRIUM ON BAY–TORONTO

Developer: Trizec Twigg Developments Limited
Architect: Page and Steele Architects

This exciting complex of prestige offices, and a two level shopping centre, constructed in three blocks, ranging in height from eight to fourteen storeys, is arranged on the north and south sides of a central east-west atrium space. A two level subgrade parking garage occupies the entire site below the lower shopping level.

The overall structure is six hundred and ninety feet long by two hundred feet wide, and is designed, for the most part in thirty feet square bays, employing modified drop flat slab construction; a framing system which was developed in-house. The modified drop flat slab differs from the conventional flat slabs in the slope and size of drops. The flat inverted, pyramid like, drops extend over 50 percent of the spans.

The superstructures on opposite sides of the atrium, are linked by various bridging elements, which in some cases are also employed to access the elevator cores, in the centre of the atrium space. The atrium spaces, which extend up to the roof level are capped off with continuous linear skylights.

The use of the modified drop system for the typical office level bays reduced the floor slab thickness by two inches. In addition, cost savings were realized by employing concrete mixes, incorporating fly ash with additional concrete compressive strength at 120 days compared to the conventional 28 days strength development.