Designers for the new mixed-use facilities at Avalon at Assembly Row in Somerville, Massachusetts, needed to ensure parking amenities were in place when the adjacent mixed-use buildings were complete. To achieve this, they created two total-precast concrete parking structures that connect to the mixed-use properties via expansion joints. The poor soil conditions in the area created additional challenges due to the weight of the multi-story precast parking structures and the heavy crane required to erect the structures.
The parking structures, consisting of a five-story, 110,472-square-foot facility and a six-story, 126,649-square foot building, were designed as total precast concrete structures consisting of double tees, columns, beams, and spandrels, with shear walls, litewalls and stairways providing lateral stability. The spandrels were finished with embedded thin brick to complement the mixed-use buildings.
The adjacent structures feature “podium” construction, with a CIP Filigree concrete base enclosing retail spaces on which four stories of wood-frame residential facilities were constructed. One of the parking structures also features retail space at the ground level, providing additional amenities for visitors and tenants.
Providing retail space on the first level of the parking structure required additional attention to ensure vibrations from the cars above would not interfere with use of the retail tenant spaces, explains Gordon Lundberg, senior project manager with McNamara Salvia, the engineer of record.
A waterproof membrane and wearing slab were applied to the lowest parking level of this garage, and a 3-hour fire separation was provided between the first-floor tenants and the parking levels above. Fire separation was achieved with specially fabricated tees and beams designed to provide a 3-hour rating. Fire separation between the parking structures and adjacent retail and residential spaces was achieved with spandrel wall panels also designed for the 3-hour fire-separation requirement.
The site’s poor soil conditions required the use of grouted aggregate piers, in which holes are displacement-augered to eliminate drill spoils and filled with crushed stone and grout. Three options were initially reviewed for foundation support, Lundberg notes, with this geopier approach providing the most economical stability. The slab-on-grade base for the parking structures and first-floor podium retail spaces rest on rammed aggregate piers, which are a lower-capacity geopier design that does not require grouting.
Additional GAPs were required to create a path to deliver the crane to position within the parking structure for the precast concrete erection. “Because this was a former urban industrial/commercial site with fill and organic soils, we had to be certain of the stability of the ground for the high garage-foundation loads as well as the massive crane that was used for erection due to the potential for soil compression along the delivery path,” Lundberg explains.
The erection went smoothly and the project opened on time in early 2014.