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Steel
Monday | 05 December, 2011 | 9:25 am

Span of steel

By Lynn Stanley

Project produces longest cable-stayed bridge in North America

December 2011- A delicate web of cables connects to 575-foot-tall concrete diamond-shaped towers creating a striking profile for the Arthur Ravenel Jr. Bridge, Charleston Harbor’s newest landmark. The 3.5-mile bridge represents the largest public works project in South Carolina history and is the longest cable-stayed bridge in North America.

The bridge, boasting an eight-lane span of steel, is also one of High Steel Structures Inc.’s largest projects ever. Lancaster, Pa.-based High Steel, an affiliate of High Industries Inc., is one of the largest fabricators of structural steel in the United States. The company’s 700-plus co-workers develop innovative processes with materials expertise to fabricate a wide range of complex bridge components and heavy building girders. High Steel also provides bridge steel erection, transportation and emergency bridge repair services.

The bridge crosses the Cooper River, connecting downtown Charleston with Mount Pleasant. The South Carolina Department of Transportation initiated the project to replace the Grace Memorial and Pearman bridges, which had become obsolete. Extensive metal deterioration plagued the bridges, which were no longer able to support heavy traffic volume or accommodate the passage of modern ships.

Retired congressman Arthur Ravenel Jr., the bridge’s namesake, helped establish the South Carolina Infrastructure Bank and worked with local officials to raise funding that would enable the construction of the new bridge.

Increasing efficiency
High Steel began work on the bridge in 2001. The company was responsible for fabricating, inspecting, coating and delivering 38,000 tons of Grade 50 and Grade 70 steel, a total of 6,194 pieces that included 40-ton girders and cable-stayed girders or shark fins designed to hold the bridge’s stay-cables in place. The state-of-the-art span was designed by Parsons Brinckerhoff and cost more than $700 million to construct. For High Steel, the design-build project began with large slabs of steel being delivered to the yards of its Williamsport, Pa., fabrication facility.

“With a design-build process, we try to weigh in early on the design in terms of how it relates to structural steel fabrication,” says Tom Wandzilak, business development manager for High Steel. “We consider what’s cost effective and what’s not so that the designer can take that into consideration when preparing the steel design.”

“We were able to refine the design to make erection of the bridge easier,” adds Scott Krause, High Steel’s operations technical manager. “We accomplished this primarily through the reduction of field pieces such as welded cross frames in lieu of knock-down frames and elimination of multiple shop splices to speed fabrication.”

Wandzilak explains the job is then broken down into unique parts dependent on the contractor’s construction schedule. “Steel is delivered to the contractor to accommodate the installation sequence,” he says.

Assembly work
Building a bridge several miles long and ensuring it meets perfectly in the center can pose a challenge. Bridge sections are erected in order to correctly size the bolt holes that are predrilled undersized. Once sections are joined and aligned with drift pins, the bolt holes are then reamed to the correct size. The last anchor edge girder or shark fin acts like a keystone representing the center of the main deck—the highest point of the deck. Cut to within a few inches of the correct length, and the piece is reduced further to link the east and west decks seamlessly. Other critical elements included designing the shark fins so bridge cables could pass through and attach to the deck to support the bridge. Fabricating these massive pieces meant bending the web to the proper angle while maintaining the integrity of the bend. Digital protractors monitored the angles during the bending and shipping phase to ensure correct degrees of angle.

Tower box girders, part of the concrete, diamond-shaped towers, held two cables that extended to the bridge deck to hold up the bridge. Each tower box girder was made with a unique angle as it moved down the tower. A laser system helped align bearing assemblies to meet work points. Pipe assemblies were welded, aligned and attached to the tower box protruding through the concrete towers. For the entire project, High Steel shipped more than 700 police-escorted loads to South Carolina.

The Arthur Ravenel Bridge opened in 2005, one year ahead of schedule. Built to withstand wind gusts of 300 miles per hour and magnitude-7.4 earthquakes, the massive structure can accommodate the world’s largest ships as well as bicyclists, pedestrians, vehicles and truck traffic. MM




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