Removing Penn Station’s Head-Knockers—Engineering Complex Structural Load Transfers

This paper addresses the structural challenges related to the concourse renovation work for New York Penn Station Long Island Rail Road (LIRR) Train Hall. This renovation has introduced an inspirational destination and offered increased width and height for the 33rd Street concourse located below 33rd Street between 8th and 7th Ave in Manhattan. This paper focuses on the challenges associated with the LIRR concourse Head-Knockers removal. Head-Knockers refers to seven deep box girders which spanned across the LIRR concourse corridor and limited the corridor headroom. In order to eliminate the overhead obstructions and open up the corridor, the removal of these girders and the interior columns was needed. This created significant changes in the load paths of the supporting system. The complexity of this work was amplified by the fact that these girders supported some of the columns adjacent to Madison Square Garden (MSG). In absence of complete existing construction documents, major field investigations were performed to generate a building information model (BIM) to understand the existing structural system. New load paths consisting of built-up transfer girders and columns were erected. These girders were supported on the new columns and cantilevered out to carry existing columns adjacent to MSG. The stiffness and strength of theses girders were designed to minimize the movement of the existing building and support their base reactions. Different loading schemes and sequences of loading were examined to ensure that the uplift on the back spans remained balanced. Each loading stage represented a different stage of demolition and construction. Connections of the new girders to the existing steel were complicated due to accessibility issues created by the presence of multiple layers of framing erected at different phases over the years. The design of these connections relied on threading new plates between existing framing to reach the unsupported members rather than framing to these members or disconnecting them. Preloading was performed to ensure the smooth transition of loading from existing to new load supporting systems and minimize the existing construction movement caused by the deflections of the new girders. Loads used in preloading were determined based on existing loading conditions and new girder stiffnesses. The self-weights of these girders were leveraged to reduce the jacking loads. Preloading of the new plate girders was controlled using a calibrated jacking system. Optical monitoring was also implemented to observe the responses of MSG and Penn Station structures during construction.