This project is comprised of a six-story overbuild of the Brown Brothers Harriman Co. building (circa 1900), as well as an adjacent 14-story addition for conversion to a residential building, including 98 apartments and tenant amenities such as a fitness center, roof deck, and game room.

The challenge in designing the overbuild was meeting code for lateral loads. Based on the team’s inspection, the columns, foundations and soil conditions were robust and tightly spaced (16’ o.c.). It was decided to engage the adjacent 28’ parcel and tie in a horizontal expansion that had sufficient capacity to support the lateral loads for the addition and the existing building. Heavy lateral loads boosted the steel tonnage for the addition to almost 20 psf.

The existing building had built up riveted steel columns. It was determined that the existing columns were significantly reduced in size at the top floor. The existing columns were then boxed in with steel plates, creating tube columns to support the load. Additionally, due to the stepped existing column sizes, all existing splices were reinforced.

During construction it was determined that the existing columns at the basement perimeter were embedded within the brick foundation wall. The porous material and water-soaked soil rotted out 50% of the existing columns. The columns were immediately shored and reinforced and encased in concrete down to the existing foundations.

Detailing of the connections between the existing and new columns was critical. Careful field dimensions limited any offset. The connecting details allowed for additional tolerances in the field taking any eccentric moments into the upper columns and into supporting girders.