Precast concrete value engineering accommodates difficult site

New construction that requires working within the confines of an old structure in poor condition is a nightmare come true for many contractors. Such was the case of the Logan Airport Central Parking Expansion Project, which required the building of a three-level, 2900-space parking structure on top of a deteriorated, five-level parking structure. The owner required the existing parking facility to remain open and functional during erection of the new structure, a mandate that severely limited many viable construction means and methods. Logan Airport's flight control tower stands immediately adjacent to the existing parking structure, and the site is further restricted on four sides by busy roadways. Facing site, structural, operational, and access limitations, engineers and designers evaluated three systems for the airport expansion project-a precast concrete system emerged as the best solution because of its economy, quality, durability, and constructibility. In this article, the project team explains a value engineering effort; special rigging and erection equipment; an exceptional foundation design; and the atypical operation of gantry-mounted erection cranes above the roof of an aged, deteriorated, cast-in-place concrete structure.