The top-down method of construction enables a high-rise superstructure and its sub-basement to be built simultaneously. Perimeter foundation walls are constructed using the concrete diaphragm or secant wall methods. Load-bearing elements or drilled shafts are installed and the building columns brought up to grade level. Ground level and first basement slabs are poured, with access holes left to allow excavation beneath. As each subsequent subgrade level is completed, the floors act as lateral bracing for the perimeter wall system. Above grade construction can proceed while the subgrade work is ongoing since the building’s structural support is already in place.
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