Parkersburg-Belpre Bridge

Parkersburg-Belpre Bridge

Shaped explosive charges have completed superstructure demolition of the 64-year-old Fifth Street suspension bridge across the Ohio River between Parkersburg, W.Va., and Belpre, Ohio. In carefully controlled sequences, the charges cut segments of the structure apart and dropped them in the river without harming a newly built replacement bridge 91 ft. away.

The old deteriorated bridge was 2,825 ft. long. Its main suspension structure had 775-ft. center span flanked by 375 and 275-ft back spans, and two 134-ft-high steel towers atop concrete piers rising 35 ft above the river’s surface. In addition, there was 1,400 ft of approach spans.

Melbourne Brothers Construction Co., North Canton, Ohio demolished most of the bridge conventionally in sections lifted out by land-based and barge-mounted cranes. But Melbourne subcontracted explosives demolition of the suspension structure’s cables and towers plus a 200-ft truss approach span to Controlled Demolition, Inc. (CDI), Towson, MD.

"We decided on explosives because we felt standard cutting would risk toppling a tower into the new bridge nearby or into the channel," says Brian W. Danaher, president of Melbourne.

Clamps flank of bridge's suspension cable cut down in diameter to ready it for blast that also demolished towers .

Toughness of the old suspension cables and their thick 8 9/16-in. dia presented CDI with a blasting challenge. Custom-designed shaped charges powerful enough to cut the cable without damaging properties in the vicinity of the blast could not be developed. "Enough explosives can be used to destroy anything," says Mark Loizeaux, CDI vice president. "But safety prevented us from using an unlimited amount. We have cut cable up to 6 ½ in. dia with shaped charges but the extra 2 in. of the old bridge cable created a problem for us."

In an action that Loizeaux terms "unprecedented," CDI reduced the cable to a thickness the charges could cut without producing harmful concussion. CDI installed clamps on each suspension cable 40 ft from the channel side of each tower. Between the clamps, in two 6-in.-long sections, the subcontractor then burned and ground away the exterior of each parallel strand wire cable, leaving a 3-in. thickness in place of the former 8 9/16 in. dia.

During the burning, workers had to avoid heating the cable to the point where it would become elastic. "We very carefully worked back and forth, burning, allowing the cable to cool, and then coming back to burn some more," says Loizeaux. "We then made the final cutting down to 3 in. with an abrasive blade saw."

Detonation of the shaped charges cut the cables at the thinned points, and dropped them into the river along with the crossing’s short truss span, which fell in six predetermining sections. The towers, then relieved of the weight of the main span cables, leaned back toward the shore, away from the channel. Charges cut each one vertically through the center and at two points horizontally. About 46 ft of each tower remained standing atop its pier to be cut apart and removed in the dry. "We didn’t want to drop anything in the water we didn’t have to," says Loizeaux. Segments that did fall into the river carried pre-attached floats that permitted quick removal and clearing of the channel in less than three hours.

The new bridge is a four-lane, 2,519-ft steel structure with a 1,500-ft cantilever truss. Pavlo Engineering Co. P.C., New York City, designed it and the prime construction contract went to Harris Structural Steel Co., Piscataway, N.J. The $17.2-million award by the West Virginia Department of Highways to Harris also included razing the old bridge.