A Piled-Raft Foundation for the Tallest Building in Brooklyn

A detailed three-dimensional finite element analysis was performed for "The Brooklyner", the tallest building [155 m (510 ft)] in Brooklyn, New York and the first structure built on a piled-raft foundation in New York City. This paper discusses the analysis of "settlement reducers" incorporated into a raft foundation. The numerical analysis was performed using the commercial finite element package Plaxis 3D Foundation. Preliminary analyses showed that a continuous raft foundation would result in unacceptable differential settlements to the structure itself, in addition to detrimental settlements at surrounding historic buildings. High capacity mini-piles were modeled below the tower core and tower edges to reduce settlements to acceptable levels. A detailed pile load test program allowed for calibration of the finite element model based on the field observations and refining the analysis to provide realistic results. Instrumentation of the raft and continuous monitoring during construction allowed for comprehensive understanding of the piled-raft behavior and comparison with the finite element study. The tower's piled-raft foundation system was the first such system to be approved by the Brooklyn Building Department Commissioner.