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Without the aid of sky hooks, NewYork City architects and engineers find innovative solutions to vertical expansion. Nowhere to Go But Up
Rooftop additions present idiosyncratic design and engineering challenges: The condition of the existing structure-whether it has adequately maintained its original load capacity and is capable of carrying additional loadsdetermines whether architects and engineers will be able to fulfill additional program requirements. Two recent but very different projects in New York City illustrate the complexities that govern this type of construction, which is becoming more common in dense metropolises around the world.
The big table
Brooklyn, New York-based Forest City Ratner Companies is building one new structure on top of another new one in midtown Manhattan. The company commissioned local architects Beyer Blinder Belle to design a300,000-squarefoot retail and entertainment complex on an infill site in the Times Square area, bordered by a parking lot on the west and commercial buildings on the east. The $290 million project called for incorporating two existing historic theaters and adding another 26 theaters for the motion picture exhibitor, AMC Amusement.
A host of peculiarities and unusual requirements early on in the project augured larger challenges down the road. The historic 1912 Empire theater was moved 180 feet to the western boundary of the 42nd Street site. The Liberty Theater on 41st Street, also an historic structure, stayed in its original place. Project Manager Jeffrey Smilow of Ysrael Seinuk Structural Engineers describes the myriad challenges. "Moving the Empire allowed us to provide it with new foundations, but the Liberty stayed on its old foundations so we had to be careful not to damage it. We designed a 20-foot-deep truss to support the AMC theaters, which spans over the Liberty at about 60 feet above the sidewalk," he explained. "If we had attempted to make the Liberty part of the new base building, we would have had to upgrade the foundations in order to comply with New York City's new seismic codes."
Having solved these problems, the architect and consultants were stunned when the owners told them that financing was available for a 25-story, 455-room hotel on top of the theater complex. Although construction hadn't begun on the theaters, the design was complete. "This is not the suburbs,"...