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DOI − http://dx.doi.org/10.4322/1809-7197.2020.99.0005 Engineering the supertall and superslender 111 West 57th

FATIH YALNIZ WSP

RESUMO

Apresenta-se em linhas gerais a concepção arquitetônica, os cificações de projeto, do edifício 111 West 57th, localizado em elementos e componentes da fundação, o sistema estrutural, Nova York, nos Estados Unidos, um dos mais altos e esbeltos bem como alguns aspectos das análises estruturais e das espe- do mundo

Palavras-chave: projeto e análise estrutural de edifícios, sistema estrutural para edifícios altos, resistência a esforços horizontais, ensaio de túnel de vento.

1. INTRODUCTION ocated just south of Central Park, the most slender high- L rise building in the world was topped out in 2019 in the heart of Manhattan, NYC among the other new supertall, superslender recently built buildings. The soaring 111 West 57th Street, with a height of 1428 ft. (435m), and a width of only 58 ft. (17.5m) holds the world record slenderness ratio of 1:24. Another new development 217 West 57th street, also completed in 2019, holds the title of tallest residential building in the western hemisphere by the height of 1550 ft. (473m). Since the completion of the first supertall 157 West 57th street in 2014—a slender residential tower rising 75 stories u Figure 1 from a small site, every new development View of the NYC skyline; the Empire State Building and 53W53 together in that area challenges the engineers to with 111W57th under construction go higher while providing unobstructed views and world class comfort expected engineering conditions on multiple construction space compounded the from a luxurious building. These new levels. A super-tall, super-slender challenges. Throughout the project, generation, small footprint structures tower in the middle of New York every design solution was supported reaching the new heights require unique City to be merged with an existing by multiple rigorous analyses and engineering solutions. landmark building, created unique design procedures. Structural solutions 111 West 57th street presented challenges for the team. Limited were developed to become one with

CONCRETO & Construções | Ed. 99 | Jul – Set • 2020 | 75 the architectural intent, leading to a foundations are adjusted around the successful and unique new icon for the existing Steinway building foundation New York City skyline (Fig. 1). with the intent of minimizing the amount of interruption of the existing structure. 2. PROJECT DESCRIPTION To address the overturning effect Located on 57th street between from lateral forces, close to 200 Rock 6th and 7th Avenues, 111 West 57th anchors/tie downs were also placed. is the latest installment of supertall, The extent of the rock anchors/tie superslender buildings on “Billionaire’s downs into the rock ranged from 50 ft. Row” (Fig. 2). The superslender structure (15m) to approximately 80ft. (25m). has a total of 68 residential floors and includes 60 condominium apartments, 4. SUPERSTRUCTURE an indoor lap pool, amenity spaces and 111 West 57th is a reinforced concrete terraces. By completion, it will stand as a building with 160 ft. (48m) of steel world-class model of innovative building crown. The gravity system is composed technologies, luxury, energy efficiency of cast-in-place concrete flat-plate and environmental sustainability. slabs supported by reinforced concrete The tower was conceived by u Figure 2 columns and shear walls. The uppermost Developer JDS Development and View of the slender 111W57th 160ft. (48m) of the tower, the “crown”, is designed by SHoP Architects. The rising with Central Park in the steel construction consisting of concrete project combines the original landmarked background on composite metal deck supported Steinway building designed in 1925 on steel beams. Steel construction is by Warren & Wetmore, and the new multiple setbacks on the south side of chosen due to limited space and multiple tower addition. In addition to the new the building creating an elegant profile. setbacks at the crown. Lateral resistance feather-like slender tower, the project of the steel crown is provided by steel involved renovating and retrofitting the 3. FOUNDATION SYSTEM braces. The crown is intended to be landmarked Steinway Building. Design One of the initial challenges of the functional and accommodates various team envisioned a tower that would project design and construction was mechanical equipments, including a extend classic 1920 style onto the the foundation. A major challenge was Building Maintenance Unit. skyline while the other towers nearby the necessity of working around the The tower structure is composed adapted contemporary approaches. existing Steinway building foundations of a robust concrete core with multiple The tower’s structure creates floor- combined with the limited footprint outrigger floors and reinforced concrete to-ceiling windows that offer views of and demands of the new structure. columns. Outriggers are horizontal rigid Central Park to the north and Midtown The design and construction process systems connecting the main core wall to the south while eastern and western required intensive coordination within a to the columns. Lateral loads are not elevations are ornate with distinctive tight schedule. It was helpful however, only resisted by the bending of the core terracotta and bronze façades.Two that the midtown area of Manhattan has alone, also by the axial tension and levels of below grade space rise to good quality substrate, with bearing compression of the exterior columns the surface and soar 95 stories above capacity of 60 tons-per-square-foot. connected to the core. Placing outriggers street level. The total height of the The foundations of 111 West in the mechanical floors increases the project is 1428 ft (435 m), including 57thconsist of concrete mat and footing effective depth improves the stiffness of 160 ft. (48m) of steel crown that also foundations with thicknesses ranging the structure. The reinforced concrete houses the Building Maintenance Unit. from 6 ft. (1.5m) to 13 ft. (4m) founded core wall system acts as the main As a distinctive feature of the building on a medium to hard (Class 1A to 1B) spine throughout the tower, providing there are a series of open floors and 60 tons-per-square-foot rock. The new support for gravitational loads as well as

76 | CONCRETO & Construções | Ed. 99 | Jul– Set • 2020 resistance to wind and seismic forces concrete shear wall sets back as the stiffness of the structure. The design while containing the elevator and stairs tower sets back in the south of the team carefully investigated several of the building’s main circulation. The building. The concrete strength and the options to increase the stiffness while thickness of the concrete core decrease respecting the functionality of the along the height of the building. The space. One of the ways to increase the shear walls are interconnected over the stiffness of the building, 4 outriggers core access openings using concrete are added at mechanical floors link beams, and where required, steel throughout the building. There is a total embedded concrete link beams. The of 10 mechanical floors in the tower core wall thickness varies along the and the location and number of the height of the tower while link beam outriggers at selected floors are based widths match shear wall thicknesses. on structural efficiency criteria (Fig. 3 To accommodate the limited space, a/b). Each addition of the outrigger floor multiple setbacks, and resulting transfers is coordinated with the other trades, at the south side of the building, several allowing continuous functionality. columns that would have typically been The mechanical equipment at each located at the south of the building are outrigger floor is accommodated by the replaced by a deep concrete beam, mechanical openings provided. leaving only two columns at the north Although the building is designed side throughout the building.The typical for both seismic and wind forces, residential floor slab thickness is 12 the building’s design is governed by inches (30.5 cm), supported by shear wind load. Due to the nature of the walls and only two columns allowing a towering, slender structure, the design column free layout for the interiors. team performed multiple wind tunnel The tower’s record-breaking tests to accurately determine the wind slenderness imposed stringent pressures and wind-induced vibrations demands on the overall strength and early in the design process. To achieve

u Figure 3a Section showing the outrigger u Figure 3b locations Typical outrigger floor plan and section

CONCRETO & Construções | Ed. 99 | Jul – Set • 2020 | 77 industry-recommended comfort criteria a three-pronged approach was taken. criteria compared to office buildings. for different return periods for residential First, open floors were introduced Taking the steps above ensured buildings and reduce overall wind loads, (Fig. 4). Open floors help to mitigate occupancy comfort for different return the vortex shedding phenomenon periods. Building response was closely that is typical of slender structures. monitored during the construction Numerous alternates for the open floors to ensure Tuned Mass Damper will were studied throughout the tower’s perform within the design range. development process including wind The utilization of high strength tunnel tests, resulting in three open concrete of up to 14.000 psi (95,6 MPa) floors effectively. Second, the mass at is imperative in achieving a building such the top of the building was increased unprecedented height and slenderness. to reduce the accelerations. Increasing Concrete strengths range from 14.000 slab mass effectively at the top of the psi (95,6 MPa) to 8.000 psi (55,2 MPa) building increased generalized mass, for the foundation, columns, and shear reducing the demand from the damper. walls, and 10.000 psi (68,9 MPa) Finally, a project specific 800-ton to 6.000 psi (41,5 MPa) for slabs. A Tuned Mass Damper was placed at concrete mix design test program with the top of the tower (Fig. 5 a/b). Tuned the concrete producers was established Mass Damper is an effective tool to to create the appropriate mix designs to control accelerations for the residential achieve desired concrete strength and buildings which has more stringent Modulus of elasticity. This was seen as a crucial element in the structural design of the building, and work on the concrete mix design was undertaken at the early design phase. In order to obtain required Modulus of Elasticity, coarse aggregate type and volume were critical and thus they were specially reviewed.

u Figure 4 u Figure 5a u Figure 5b Section showing the open floors TMD detail TMD detail

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high strength reinforcing steel, spliced compensations to be implemented by means of mechanical connectors, during construction. The building was utilized in columns and shear walls was regularly monitored during the at the lower portion of the building. construction for axial deformations. Utilizing high strength reinforcement in lower floors minimized the reinforcing 5. WIND TUNNEL TESTING congestion while reducing the Wind Tunnel tests are an important construction effort. Reinforcement, part of the design process, performed preassembled outside in cages, was with varying surrounding considerations. transferred to construction site. Establishing the wind climate, Axial shortening due to changes understanding wind’s behavior at in structural members as a result of different strata, direction and frequency elastic, creep and shrinkage effects of occurrence, understanding the over time, is an important consideration building’s aerodynamic and aeroelastic in super slender buildings. Appropriate response and making subsequent calculations were performed by adjustments to the building’s geometry using three-dimensional sequential to mitigate wind effects were key u Figure 6 construction analysis taking into measures taken for a successful 3D analysis model consideration the different scenarios project. The studies regarding structural (Fig.6). Based on the construction engineering, architecture and wind In addition, the high strength schedule, multiple models were tunnel testing of the tower were very concrete used for the thick concrete developed to accurately estimate closely intertwined throughout the walls, defined as mass concrete, the required elevation and position development of the project (Fig. 7). required a particular concrete mix to meet the most stringent of demands. Industrial by-products such as fly ash, granulated ground blast furnace slag cement and silica fume were used to replace more than 50% of the cement content to reduce and slow the heat of hydration. Self-Consolidating Concrete (SCC) was used for all concrete requiring strengths greater than 8.000 psi (55,2 MPa). Due to the high density of reinforcing steel at the base of the building, most of the (SCC) mixes were consolidated with internal and external vibrators. During the construction, concrete was regularly sampled and test results were documented. The increase in concrete strength resulted in a significant reduction in the u Figure 7 overall size of structural elements while Wind-tunnel testing providing greater stiffness. Furthermore,

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Comprehensive and project- only for 1 year return period, TMD is A unique and challenging specifi c wind tunnel tests were designed to meet the acceleration building like 111 West 57th enables performed at the Rowan Williams & criteria for 1 month and 10 years the engineering team to apply the Irvin (RWDI) wind tunnel facilities to return periods. accumulated knowledge gained determine more accurate wind loading through previous experience and wind response of the tower with 6. SUMMARY enhanced with forward thinking respect to human comfort criteria. 111 West 57th incorporated advances in structural practice. High Frequency Force Balance numerous advanced engineering The combination of structural (HFFB) and Aeroelastic tests were solutions to achieve the luxury, engineering with exacting wind performed at different stages of the height, and slenderness ambitions of tunnel testing, and the collaboration design. Results guided the team in the the project. This unique building has with the architect and development design, including determining the most pioneered new frontiers of engineering team intertwined harmoniously effi cient location of the open fl oors. to emerge as the world’s most throughout the trajectory of the The acceleration results at the slender building, while embracing project. The result is a highly highest occupied fl oor for different a classic architectural design style. complex, innovative and elegantly return periods meets the criteria From early on, it was of the utmost proportioned tower. The aspirations of human comfort for residential importance for the team to foresee the of the entire project team have buildings after placement of a project- challenges, and develop procedures added a new and unique grand specifi c 800-ton Tuned Mass Damper. and innovations supported by multiple icon to complement the New York Although ISO addresses accelerations rigorous analyses. City Skyline.

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