HEAVY LIFTING NEWS: Strand Jacks Star in NJ Bridge Demolition

Engineered Rigging combined its design, fabrication and heavy lifting expertise to help a contractor dismantle and remove the 90-year-old Wittpenn Bridge in New Jersey. The challenging work included lowering two counterweights estimated to weigh nearly 450 tons each and a 209-foot-long vertical lift span weighing nearly 900 tons.  Adding to the difficulties, crews maneuvered in close proximity to a nearby railroad trestle and battled winter storms and frigid temperatures.

Before removal of the counterweights and main span began, Engineered Rigging assessed the vertical lift bridge’s structural integrity. For nine decades the bridge weathered countless storms, nor’easters and hurricanes, and carried over 50,000 vehicles a day between Jersey City on the east and Kearny on the west.

The company’s engineering team conducted several engineering studies to identify risks and optimize safety precautions. They analyzed the existing structure using computerized modeling to ensure the forces put on the bridge during the controlled lowering would not damage the structure.

“Our analysis revealed that the bridge was not strong enough to simply grab and lower,” said Christopher Cox, P.E., co-founder and president of Engineered Rigging. “We needed to add steel beams and clamping fixtures to ensure its structural integrity.”

Engineered Rigging determined that a strand jack system was the most suitable heavy lifting equipment for this project due to its high capacity, compact footprint and ability to provide precise control for load lowering up to 100 feet. Whenever possible, the strand jacks would attach to the existing bridge structure including the main tower sheaves and ropes, lift girders, towers and floor trusses.

To expedite project design, Engineered Rigging’s team of engineers and project management simultaneously developed two engineering plans—one to lower the counterweights on the east and west ends of the bridge and another to lower the main span. This parallel development facilitated the New Jersey Department of Transportation’s (DOT’s) extensive submittal review.

Custom Fabrications Connect System to the Aging Structure

When the lift plans were complete, the necessary steel fabrication work began at Engineered Rigging’s fabrication shop in Russellville, Arkansas. The company completed more than 400,000 lbs. of steel fabrication in just five weeks. For the lowering of the counterweights, Engineered Rigging fabricated custom attachments called dog bones [see photo below] to secure four inverted 200-ton strand jacks under the main span lift girders. We also fabricated a transfer fixture designed to allow the decoupling of the main rope spelter sockets from the lift span and allow the lowering of the counterweights to just above the bridge deck for demolition.

Embracing the Unexpected