Excerpt:
Roof lifted above
the stars
'...Tricky. Renovating a post-tensioned slab is tricky. Slab penetrations first require detensioning and the retensioning of the cables. If a cable snaps, it recoils and rips through the concrete, shooting pieces everywhere...
"This is a first, but not because of its size," says Peter M. Vanderklaauw, veteran roof lifter and president of project subcontractor Liftplate International, Inc. The challenge here is the concrete columns, he adds. "...
The team considered demolishing the roof and adding new structure. But "cost and logistics became prohibitive," says Douglas Wood, of the Coral Gables, Florida structural engineering firm that bears his name. Demolition alone would have cost $350,000. The lift cost a total of $600,000.
But cutting the columns for lifting did require extra steps. In concrete structures some bending forces in the slab are transferred into columns, says Wood. "When columns are cut, bending is transferred back into the slab, creating the possibility of downward movement at midspan.
"To compensate, we added external post-tensioned cables in both directions," says Wood. A steel bracket installed at midspan gives the cables a triangular profile... '
Download the Full Article in PDF format
RETURN TO NEWS
