World's tallest lab: architects from Skidmore, Owings & Merrill offer an inside look at building the world's tallest lab.
Building a giant
Three structural design constraints complicated the structural analysis. First, a 13-story section of the 24-story tower cantilevers 30 ft over the existing low-rise MSK-Laboratory to facilitate the 3 part phasing for the construction. This section caused significant structural engineering design challenges, including magnified P-delta effects, gravity drift, in-plane diaphragm forces, progressive collapse concerns, structural steel and exterior wall tolerances issues, and a need for column tension anchors. Secondly, the floor systems and overall lateral system in the tower were designed according to strict vibration response criteria and overall motion perceptibility control to ensure a suitable environment for the scientific equipment they would support. Finally, construction of the tower was complicated by a highly constrained site and a 70 ft deep rock excavation.
The tower lateral system is composed of different types of structural steel frames and trusses designed to resist loads from all directions. Moment resisting frames comprise W30 series beams and columns located at the east and west sides of the lab prism. X-braced frames comprise W14 series columns and diagonals and W24 beams joining the moment resisting frames at the north and south ends to form a complete tube structure. Belt trusses at the two mechanical zones further integrate the frames and enhance the redundancy of the lateral system. Diagonalized core trusses are located in the main elevator zone in the middle of the east zone. Double sets of 30 ft high outrigger trusses at the two mechanical zones extend across the width of the building and engage the moment resisting frames, belt trusses, and a set of gravity columns.
The 13-story cantilever zone--a significant feature of the tower--is supported by two lines of double-story W14 series diagonals. These lines of diagonals are offset from the lateral force resisting frames and rely on the concrete floor diaphragm to transfer horizontal forces to the lateral system. The floor diaphragm transfers the forces by acting as a continuous, 90 ft deep I-beam, with the concrete slab acting as web and moment resisting frames acting as flanges.
Analyzing a giant
Building engineers used non-linear analysis methods to analyze the building structure and evaluate the magnitude of P-delta effects and global buckling behavior. P-delta effects, resulting from the magnification of member forces due to building lateral drift, were important for this project due to the potentially destabilizing effects of the cantilevered zone. The analysis showed that the building structure, proportioned to limit gravity and wind drift, was adequate. Global buckling analysis verified that the core truss, with one story diagonals, braced the X-braced frame six story diagonals between truss nodes.
The typical floor system is composed of a three-inch deck with 4.5 in of normal-weight concrete above the deck acting with the steel framing to form a composite system. The floor system is supported by the lateral force resisting frames and W14 series gravity columns. The MSKCC tower floor system was designed to criteria more stringent for resonance behavior than that used for typical buildings. To achieve 2,000 gin/sec velocity limits, the concrete slabs, beams and girders were increased one size (e.g. W21 to W24).
Basement excavation was the longest and most difficult construction phase. Ten ft of fill separated grade and bedrock Manhattan schist. To create space for the 75 ft deep basement levels, the contractor excavated a volume of 66,000 cubic yards to a depth of over 70 ft below the bedrock surface--making it among the deepest building construction excavations in the world. It was necessary to cut the rock over 70 ft deep, the deepest rock cut for a building in the City of New York. Rock was removed by line drilling and blasting. Blasting was closely monitored to minimize adverse effects on the adjacent church, a masonry structure with historic value, and Kettering Laboratory, which was conducting sensitive, long-term, experiments.
Find the full length version of this article 'World's Tallest Lab' go to http://www.rdmag.com.
--Charles Besjak, SE, PE, Shane
McCormick, SE, PE, and Dmitri Jajich, SE.
Skidmore, Owings, Merrill LLP
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|Title Annotation:||Expanded Article Online|
|Comment:||World's tallest lab: architects from Skidmore, Owings & Merrill offer an inside look at building the world's tallest lab.(Expanded Article Online)|
|Publication:||R & D|
|Date:||Aug 1, 2005|
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