Two cast-in-place concrete arch bridges support the existing roadway. One was built in 1934 by Robert Moses as part of the original four-lane SSP and today spans the eastbound lanes. A second arch bridge, matching the original, was constructed in 1960 when the parkway was expanded to four lanes in each direction. It spans the westbound lanes with its north footing abutting the older structure’s south footing.

Both bridges needed to be widened on both sides to stay within the right-of-way and avoid impacting a nearby cemetery. The New York State Department of Transportation also required the construction to preserve the landmark features of the original bridge. Babylon, N.Y.-based Greenman-Pedersen designed the expansion with four new arch structures built along both sides of the existing arches, one in each quadrant of the interchange.

The new additions were designed as precast units to avoid blocking traffic with shoring beneath the structure. The span lengths precluded the use of a single precast arch section. Instead the designers specified pairs of semi-arch units connected with a cast-in-place closure pour.

Posillico Civil, Farmingdale, N.Y., the contractor, and Middlebury, Conn.-based GeoDesign, the structural engineer, devised a unique erection scheme for the semi-arch units. New foundations with vertical stem walls extending 6-ft. above the footing were cast-in-place alongside the existing foundations. Six #11 anchor rods protruded from the stem walls.

To install the precast units a 4-ft. steel strut was bolted to one of the semi-arch units. Two cranes, each lifting one semi-arch unit, positioned and threaded the stem wall’s anchor rods through holes in the abutment end of the unit. The holes were grouted and rods bolted on top.

While suspended in midair, the strut extending from one of the semi-arch units was bolted to its partner to complete the arch and hold it in place without shoring from below. A cast-in-place transverse closure pour then permanently tied together the two arch segments at the top.

The granite stone facades and ringstones were removed from the old structures prior to construction. The stones were cut for reuse as a 6-inch veneer on the new structures.

The project was completed in June 2009.

Key Players

Owner/Contact: Suffolk County Dept. of Public Works, Yaphank, N.Y.
Designer, Construction Support Services & Construction Inspection: Greenman-Pedersen, Inc., Babylon, N.Y.
Contractor: Posillico Civil, Farmingdale, N.Y.
Precaster: The Fort Miller Co., Inc., Schuylerville, N.Y.
Structural Engineer: GeoDesign, Inc., Middlebury, Conn.
Precast Arch Erection: Northeast Structural Steel Inc, Mt. Vernon, N.Y.
Stone Work: Graniteworks, Inc., Deer Park, N.Y.