A previous edition of Explainer described how a raft slab provides strong foundational support to a new building. When construction soars above grade, multi-storey developments — especially those with large podiums — often require additional structural stability to handle the excessive weight of the building. 

In order to transfer the massive load of a skyscraper to perimeter support posts and through to the foundations, a huge tabletop-like slab is constructed out of concrete and reinforced with rebar and post-tensioned tendons. Called a transfer slab or transfer beam, the complex undertaking is one of the most important, and longest to complete, tasks in the construction of a multi-storey building.

Construction of the thick transfer slab at Aura in Toronto, image by Forum contributor androiduk

In Toronto, the 78-storey Aura at College Park instituted a transfer slab on the fifth floor to shift the loads of the 71 levels above. The 2.5-metre-thick slab was poured in sections and took most of the summer of 2011 to complete. A few blocks to the west, a transfer slab will be built atop an existing building to permit 37 additional floors as part of the 488 University project. In preparation for this feat, steel beams and cross bracing are being installed on the building's perimeter to support the upcoming floors. 

Cross bracing is installed at 488 University to support the incoming tower above, image by Marcus Mitanis

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