Demolition of four river crossings and approaches. Design of improved interchange, new pedestrian/bicycle bridge, and streets. Contaminated materials, wetlands protection.

Weidlinger Associates provided structural engineering to Jay Cashman and Testa Corporation, JV, for demolition of the Grace Memorial and Silas Pearman Bridges over the Cooper River and Town Creek in Charleston, SC. Each bridge consisted of two crossings with through trusses approximately 600 feet and 1,000 feet long. In addition to the removal of the piers, approaches, and all debris, the scope of work encompassed design and construction of interchange improvements and enhancements, including new streets, sidewalks, and pedestrian/bicycle bridge. The project posed numerous environmental challenges, including containment of contaminated materials and protection of sensitive wetlands. Demolition began in August 2005 and was completed in early 2007. The majority of the disposed concrete bridge material was placed offshore to form thirteen artificial reefs at various locations off the Charleston coastline.

Built in 1929, the 2.7-mile-long Grace Memorial Bridge had a steel superstructure and steel bents. The Silas Pearman Bridge, built in 1966, was also about 2.7 miles long. In addition to two identical through trusses, it consisted of a steel-and-concrete superstructure with concrete piers. During demolition of the piers in the Cooper River, the use of cofferdams around the piers in the river’s navigational channel protected the new piers and shipping traffic and facilitated the removal of deep foundations. The Pearman piers on the Mount Pleasant side were retrofitted for construction of a new observation pier.

The bridges were replaced by an adjacent cable-stayed bridge, which remained in use during the demolition. Because the SCDOT and the City of Charleston limited night and weekend street closures within city limits, most demolition had to be performed quickly from the superstructure above or at grade level. Superstructure elements were removed individually or as a section over land and water. Within the State Port Authority area, challenges included protection of the adjacent boat house, storage boat racks and marina, South Carolina Public Railway, and existing utilities and roadways.

Over the Cooper River, the truss suspended spans of both bridges were lowered onto barges using four 960-ton-strand jacks, to meet the criterion that the river’s shipping channel be closed for no more than 24 hours. This entailed designing the jacking beam assemblies, analyzing the cantilever and suspended span for loads and deflections, determining optimum cut locations on the truss members, and developing the construction sequence. In addition, the suspended span was analyzed to ensure that the members were not overstressed when lowered and secured onto the barge. Lowering operations for both suspended spans were completed in less than 12 hours. The removal of girders over water required careful sequencing; individual girders and pair of girders were removed with barge-mounted cranes.

Completion Date: 2007
Location: Charleston, South Carolina
Owner or Client: South Carolina Department of Transportation
Prime Consultant(s): WAI Prime; Jay Cashman/Testa Corp (JV)