The Ritz-Carlton Luxury Condominiums and Four Star Hotel is a 40-story mixed-use building situated at the southern most tip of Manhattan. The property has achieved a unique distinction in showcasing world-class architecture at the gateway to Manhattan. This mixed-use development also has the distinct honor of being the new home of the New York Skyscraper Museum. In addition, the 40 stories, include three floors with public areas (restaurants, ballrooms, meeting areas museum and mechanical level)ten floors with 298 hotel rooms and amenities, and sixteen floors with 140 luxury condominiums.
The location of this structure posed many challenges for design and construction. The proximity to the Hudson River and the required depth of excavation necessitated a foundation and excavation retention system capable of holding back as much as 18 feet of water pressure. The foundation walls and slabs also had to be designed to resist this significant hydrostatic force. Wall thickness varied from 14- to 16-inches and two-foot thick steel reinforced concrete slabs were used to resist both upward and downward pressures between the pile caps.
To support the building loads at the base, while minimizing the extent of excavation, dewatering and waterproofing, the pile design selected was a 200-ton steel pipe filled with 10,000-psi concrete. The weight of the building required a total of 600 piles, which extended through 40 feet of hydraulic fill to bear on solid bedrock.
The conditions of the soil below this irregular shaped structure required that a dynamic response spectra analysis be conducted to accurately predict the behavior of the structure during a seismic event. The design for seismic loads also considered the high wind loading potential at this site. A coupled shear wall system was elected to provide lateral load resistance to the high winds of the New York Harbor with a constant thickness of 12 inches. The added construction speed and convenience provided by a constant thickness concrete wall was achieved by deploying high strength concrete and varying the strength from 5,000 psi to 10,000 psi.
Overturning resistance at the building foundations was accomplished using a 7-foot thick reinforced concrete mat. The mat extended out to engage the overturning resistance of heavily loaded gravity columns and the overturning resistance of the piles. This system effectively formed a “Base Outrigger” to minimize base rotations and eliminate the need for rock anchors.
Cast-in-place concrete was selected as the material of choice because its speed for this application. The two day per floor construction cycle perfected in New York allows the building to be constructed rapidly. Flat plate construction minimizes the floor to floor heights while providing a smooth ceiling surface requiring no additional framing for hotel rooms and condominiums. The underside of the concrete is simply plastered. Flat plate construction affords long open spans and cantilevered corners while allowing for full flexibility in location of columns. This flexible arrangement of columns is called a “shotgun pattern” and is not practical with any other type of construction.
The gravity loads resisting system is a conventional reinforced flat-plate slab supported by columns and walls. Spans in excess of 30 feet and corner cantilevers extending as much as 14 feet in both directions necessitated the use of a 9-inch slab. After a detailed finite element analysis of the floor systems, the stresses and deflections were determined with higher precision. Slab cambering was necessary to eliminate initial dead load deflections in many of the long span areas. High strength concrete ranging up to 10,000 psi was also utilized. The requirement of a column-free ballroom space with a maximum ceiling height at the second floor was accomplished by transferring an entire line of building columns. Due to the depth restriction of 42 inches, post-tensioned transfer girders were used. Each girder contains 120 monostrand tendons arranged in a draped profile. The tendons were tensioned, or “jacked, in two stages in order to account for construction sequencing. Other conventionally reinforced transfer girders as much as 10-feet deep were used to transfer columns at other locations.
In addition to faster construction and excellent fire resistance, the concrete framing systems provided this structure with inherent damping benefits to resist movement due to high winds at the tip of Manhattan. With the added stiffness, minimum vibration and sound transmission, concrete buildings enjoy high levels of tenant comfort and are occupant friendly. In this project and many others, cast-in-place concrete construction also allows last minute changes to be incorporated easily in the field with minimum or no interruption to fast-track project schedules.
Podium East facade with its many jogs, setbacks and overhangs.
Large transfer beams were used to transfer heavy tower columns.
Monostrand tendons in a post-tensioned beam being laid out.
The curved facade allows the hotel floors unlimited views.
Post-tension transfer beams and tendon profiles.
"Staggered" construction sequencing.
Millennium Partners, Chicago, Illinois
Gary E. Handel & Associates, San Francisco, California
Polshek Partnership Architects, New York, New York
DeSimone Consulting Engineers, New York, New York