1875 Pennsylvania Avenue in Washington, D.C.



Thornton Tomasetti provided structural design for a 316,000-square-foot office building that interconnects to adjacent buildings, one on each side, to create a combined 600,000 square feet of office space leased by a single tenant. The building includes 13 stories above two occupied basement floors and three levels of below-grade parking.

The spread footing foundation required substantial underpinning at the west side to accommodate the below-grade sections, which extend below an existing building. The superstructure consists of two-way concrete slabs with post-tensioned slabs above grade. Long-span post-tensioned spandrel girders and a cantilevered corner bay are used in the rear of the building to create column-free truck turn-outs in a tight alley.

The west side of the building features a full-height atrium that culminates in a skylight roof and a 115-foot-long glass curtain-wall that rises 30 feet above the adjacent building. Cantilevered floor slabs extend progressively westward, with the introduction of transferred sloping columns into the atrium as the building rises. The trapezoidal portion of the curtain wall facing the street is laterally braced at each floor by Vierendeel pipe trusses but is designed so that the gravity load is hung from the atrium roof, creating a column-free expanse of glass.

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