Anchors away: Steel screws support massive stone cornice

August 11, 2010

The building team renovating the historic Tweed Courthouse in New York City employed a novel technique for supporting a replacement marble cornice that runs the perimeter at roof level.

"The weight of the cornice places a tremendous load on the rest of the stone facade," says Jack Waite, principal of architecture firm John G. Waite Associates. "We had to think of a method of supporting that load."

Approximately 1,800 6-ft.-long, stainless-steel threaded anchor screws were combined with z-clips to support the 900 feet of marble cornice. The screws are inserted 5 feet deep into predrilled holes in the building's existing backup stone and are grouted in. Each individual cornice piece-which weighs 3,500 pounds-is supported by five anchor screws.

Waite says that although the steel anchoring system is a rather high-tech method of supporting the large cornice pieces, it was actually a less complex alternative than other, more traditional techniques that the building team was considering.

"These huge cornice stones had fractured over the years, so what we decided to do was shear the stone away at the building face and fasten new pieces of stone to that existing mass with the steel rods," he adds. "Originally, we were going to take away all that existing mass and pour concrete in its place, which would have been more complex structurally."

         
 

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