2017-acec-75-rock-000

75 Rockefeller Plaza Wins ACEC Engineering Excellence Award

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The Judges in the 2018 Engineering Excellence Awards Competition have selected the 75 Rockefeller Plaza for an ACEC New York Platinum Award in the category of Structural Systems.

75 Rockefeller Plaza is a landmarked 33-story steel moment frame building constructed in 1947 for Rockefeller’s Standard Oil Company, totaling 623,000 square feet, with typical floor plates ranging from 14,000 to 30,000 square feet.

RXR has undertaken a major repositioning, which includes a restoration of the building façade and base metalwork, retail and lobby enhancements, and new mechanical systems and infrastructure. The full repositioning of the building began in 2014. This work included a reconfiguration of the lobby into a double height, 24-foot high space connecting 51st and 52nd Streets.

The lobby renovation required the removal of four columns at the ground floor, three of which supported existing transfer girders. Multi-story transfer trusses and removal of each column from the top down were among the schemes considered before the final design of a composite steel box girder was selected.

The unique box girder solution (as opposed to a pair of built-up wide flange beams) coordinated nicely with the planned sculpted lobby ceiling, which required the transfers to be as narrow and shallow as possible. The composite box girder had to be carefully specified, as this configuration and method are typically applied to bridges rather than buildings. Both AISC 360 (national specifications for structural steel buildings) and AASHTO (regulations of transportation infrastructure) were consulted.

To preload the girders, a yolk system with 500-ton jacks maintained redundancy and did not require any temporary structure or shoring. The method pushes the girder and pulls the column below up, loading the girder in flexure without any significant displacement. At that point, the final connections are completed and the existing column removed.

This landmarked skyscraper has represented the forefront of innovation in the engineering professions since it was first built (at the time the tallest air-conditioned building in the city). Its renown casts a spotlight on the latest modernization techniques. Employing a variety of structural steel codes fosters a new way of thinking about novel applications of structural design.

The landmarked façade features new energy code compliant windows with historic profiles. Its restoration and enhancement required approval by the New York City Landmarks Preservation Commission. Remaining true to the building’s history, the developer demanded the modern elements that tenants expect: a functional, elegant place to do business. The comprehensive redevelopment delivers the most technologically advanced and efficiently operating structure in Rockefeller Center. The building anticipates LEED Gold certification.

Effects of column shortening and resistance from the steel moment frame above were all considered during the loading process to transfer the lobby columns. Maintaining the building’s lateral stiffness was a primary focus throughout the project. The building was originally designed under the NYC 1938 code, which included no wind or seismic requirements, and therefore accounts for a small amount of lateral stiffness relative to modern buildings. Careful attention was paid to reinforcing connections and keeping the relative increase of loads in all members to a minimum.

A scaled 3D model and a video of the transfer assembly process were produced to help communicate to the steel fabricator and the owner the design concept and erection/preloading procedures for the new steel box girder around existing transfer girders.