Cambridge, MA – As the structural engineer of record of Broad Institute, McNamara/Salvia Inc. (Mc/Sal) worked with the design team and owner to design a structure that provides design flexibility within budget constraints.
A major challenge for the design of this 16 level structure was the tight building site partially occupied by an existing eight level post-tensioned concrete parking garage that was to remain. The fact that the existing garage was not originally designed to support a future building above provided additional challenges beyond just the site logistics, as did the need to put new openings through the existing post-tensioned slab.
Mc/Sal designed a composite steel floor system with a steel braced framed core augmented with steel moment frames for lateral load resistance to provide an economical structural system that also provided flexibility for space planning. Floor-to-floor heights were typically 15 feet for lab floors and 20 feet for the three mechanical floors. The footprint of the upper floors of the building overlapped with two bays of the existing garage.
In order to maintain the function of the garage, new columns for the building could be located only on the garage column lines between the parking tray and the ramp. The required column layout on the lab floors resulted in a major column line being located over a primary drive aisle in the garage. To support the columns loads from 11 levels of new structure over the existing garage, Mc/Sal designed double 72” deep steel plate girders on the sixth level to transfer loads to 95 foot tall steel box columns which were threaded through the garage structure.
In the basement, new high capacity drilled mini-piles were installed between the existing garage footings. The pile caps were reinforced with W40 steel beams to spread the load evenly to the mini-piles in the tight space.