A fine finish

Case Studies
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Normally, paving a 172-ft-long bridge doesn’t pose a challenge. Throw in a large skew angle, T-beams with a significant camber, a slight crown and a vertical curve, and the mundane now tests the skills of the most seasoned contractor.

Manhattan Road & Bridge, Tulsa, Okla., faced such a complex bridge in Benton, Ark. The Edison Avenue Bridge’s design included 168-ft-long T-beam steel girders made with a 13-in. camber and a 59° skew angle, which shifted the camber point of each beam that had to be taken into account.

The deck’s 2% crown and substantial vertical curve—5.85% on the uphill and -4.85% on the downhill—added to paving complexity.

“This bridge project had all the challenges you could get,” said Johnny Bowen, project superintendent for Manhattan Road & Bridge.

Paving with the skew

Bridge deck width measured 65 ft 2 in., including the sidewalks. The steel girders were set to an 8-ft 4-in. center, if the bridge were square. Measured at the skew angle, however, header centers ranged from 12 to 15 ft.

Deck thickness varied from 9.38 in. to the bottom of the pan to 9.75 in. over the haunch in the beam. With spec tolerances requiring thickness variations of less than 0.25 in. on the low side and 1 in. on the high, “our greatest challenge was getting the right deck thickness,” said Bowen.

Manhattan purchased a new Terex Bid-Well 4800 paver specifically to pave this complex bridge deck. With its 48-in. truss depth, the 4800 offers bridge contractors paving widths ranging from 15 ft to more than 170 ft.

While the bridge width was only 65 ft, the 4800’s paving width was set at 121 ft to compensate for the skew.

“By aligning the paver to the angle of the bridge, the paving carriage hits the same deflection point on the beam, keeping the grade consistent,” said Larry Eben, southeast area manager for Terex Bid-Well.

Manhattan purchased the optional skew bar kit, specifically designed to compensate for paver frame setup on the bridge. Bowen estimated that the legs of the paver were approximately 18 ft apart from each other on the rails.

“The kit allows the paving carriage to be offset, so it hits the same crown points from the front to the rear of the machine,” said Eben.

Crews first paved the 170-cu-yd center bridge span to address the T-beams’ significant camber. Less than a week later, Manhattan finished paving the bridge deck by pouring 85 cu yd on both 40-ft end sections the same day.

When crews finished pouring one end, the operator raised the paving carriage and “walked” the machine over the previously poured center.

“Our standard hydraulic carriage lift offers 5 in. of lift for just such a need,” said Eben. Once clearing the center section, the carriage automatically resets to its pre-established paving setting, allowing the crews to quickly finish the final pour.

A final inspection showed that Manhattan and the 4800 paver successfully completed the job and met the project’s demanding thickness specifications.

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