Thornton Tomasetti was retained by FC Beekman Associates, LLC to prepare a protection and monitoring plan for the existing buildings at 140 and 150 Nassau Street. The protection plan was motivated by the proposed mixed-use tower development at Beekman Tower, which is located to the east of the existing buildings.
Since the existing buildings are individually designated Landmarks, the Plan must minimally conform to New York City Technical Policy Procedure Notice 10 of 1988 which requires procedures for the avoidance of damage to historic structures within 90-feet of adjacent construction. Thornton Tomasetti performed detailed interior and binocular surveys of the designated landmark buildings and hands-on inspection of sculptural terra cotta caryatids at the corners of 150 Nassau. Based on our experience in new buildings, we also reviewed and commented on the developer’s foundation design and intended construction methods. We developed a monitoring plan that included alerts at lower vibration thresholds so the project team would have advance warning of potential problems “before” they occurred based upon the archaic structural systems and materials of these historic buildings. This program avoided significant damage to the historic buildings as well as allowing the new construction to proceed on schedule. Protection measures included foundations, building superstructure, facades and roofs, interior and exterior finishes as well as gas, water, and electrical services.
Thornton Tomasetti also performed periodic observations of the building interior and exterior finishes during the excavation and foundation construction of the Beekman Tower. We also responded to calls from all involved parties about various conditions and concerns including possible vibration excesses and cracking.
Even though the maximum limits of vibration established for historic properties by New York City were never exceeded, some minor settling and cracking did occur but nothing structurally significant which highlights the need for this type of monitoring.
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