The Marriott Marquis is a 15-story hotel with 1,224 guest rooms surrounding an atrium lobby, ground-floor retail and restaurants, a 5,200 square-foot outdoor event terrace and a two-story fitness center. Seven below-grade levels house 105,000 square feet of event space, including three double-height ballrooms; mechanical and back-of-house areas; and parking for 400 cars. The hotel also integrates a renovated historic building. Fitting the hotel’s 1.25 million square-foot program on a tight 100,000-square-foot site and within Washington’s strict height limits required the use of top-down construction and innovative structural design.
While the superstructure consists of standard flat-plate concrete, conventional structural systems stopped at grade. Site constraints ruled out standard bracing methods for the 100-foot-deep excavation, making top-down construction necessary. After installation of a slurry wall, composite steel interior columns and drilled-shaft foundations, the highest basement slab was poured. Then excavation for the next slab down progressed as a mining operation and the steel columns were encased in high-strength concrete. This allowed the slabs to act as diaphragms to brace the slurry wall. Superstructure construction began while basement levels were still being excavated.
Innovative Steel Design
The below-grade ballrooms required creative structural design to control settlement of the 15-story tower above. Eight massive steel-plate transfer girders span above the 30,000-square-foot grand ballroom and support the superstructure’s columns. Two of these girders were preloaded before tower construction began, straightening an initial camber of 4.5 inches. As construction progressed – loading the girders with the weight of the structure above – the preloading was incrementally relieved. At completion, the trusses were straight, keeping the structure level.
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