Edison span carries difficult skew
A 172-ft bridge over railroad tracks in a sleepy Southern town typically doesn’t pose much of a challenge. Throw in a large skew angle, T-beams with a significant camber, a slight crown and a vertical curve, however, and the seemingly mundane now tests the skills of even the most seasoned bridge contractor.
Tulsa, Okla.-based contractor Manhattan Road & Bridge faced such a complex bridge project in Benton, Ark., last paving season. Part of a two-year, four-bridge job for the Arkansas State Highway and Transportation Department, the single-span Edison Avenue Bridge over the Union Pacific Railroad tracks was an extremely difficult deck to pave.
The bridge’s 168-ft-long T-beam steel girders were made with a 13-in. camber. That alone isn’t cause for great concern. However, the bridge’s 59° skew angle shifted the camber point for each beam, which had to be accounted for when paving the deck.
A substantial vertical curve added to paving complexity.
“The design included a positive 5.85% vertical curve on the uphill and a negative 4.85% on the downhill,” explained Johnny Bowen, project superintendent for Manhattan Road & Bridge. The deck’s surface also included a 2% crown. “This bridge project had all the challenges you could get,” he added.
The Edison Avenue Bridge is 65 ft 2 in. wide and includes sidewalks on each side. The steel girders were set to an 8-ft 4-in. center, if the bridge were square. However, the skew widened the headers to between 12 and 15 ft. A 4,000-psi, Class 5 FAE concrete mix was poured over the corrugated metal deck pans.
Deck thickness ranged from 9.38 in. at the bottom of the pan to 9.75 in. over the haunch in the beam.
“Our greatest challenge was getting the right deck thickness,” said Bowen. Spec tolerances were tight, as paving crews could only miss target thickness by 0.25 in. on the low side and 1 in. on the high.
Manhattan purchased a new Terex Bid-Well 4800 paver specifically to pave the complex Edison Avenue Bridge deck. The company equipped the new paver with special options to aid in dealing with the grade, skew and finish of the bridge deck.
“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,” explained Larry Eben, Southeast area manager for Terex Bid-Well.
To help align the paver and carriage, Manhattan purchased the optional skew-bar kit, which is specifically designed to compensate for frame setup on the paver.
“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,” added Eben.
Due to the bridge’s complex design, Bowen admitted, it took a while to set the machine to pave the crown, skew and vertical curve, but once everything was set, the crews ran into no problems.
Less than a week later, Manhattan finished paving the bridge deck, pouring both end sections the same day. When the crew finished pouring one end, the operator simply raised the paving carriage, “walked” the machine over the previously poured center, lowered the paver back to its pre-established paving setting and finished the final pour.