The recently constructed Pond Creek Bridge on US460 in Pike County, Kentucky had an unusual construction method used to build it. More popular in Europe, incremental bridge launching is ideal when a bridge is very high and access via traditional cranes is difficult or impractical.
The bridge, which is the tallest bridge in Kentucky and one of the tallest in the nation, was constructed by Bush and Burchett Inc. of Allen, Kentucky. Coming in at 324 feet, the height and the rugged terrain of the project site posed unique challenges for the contracted company.
"Being 320' tall and only 1000' long, the slopes on each side of the bridge were extremely steep," commented Paul Burchett, co-founder of Bush and Burchett. "This made conventional erection almost impossible."
Bush & Burchett partnered with Engineered Rigging to build the steel bridge on the embankment, and incrementally move the girders into position on the eight sets of piers.
They utilized equipment such as two 70-ton strand jack rentals, a SLPP7E strand jack pump, strand guide, strand recoiler, gold box, and industrial Hilman rollers. Engineered Rigging provided an on-site technician to operate the strand jack system. As construction of one section of girders was completed in the launch bay, the strand jack system was used to pull it onto the bridge pier, which allowed the next section of the bridge to be constructed on the embankment.
In order to put the entire bridge into position, you need 10 jacking evolutions, and 8 are already complete. The pulling weight for the first pull was approximately 16,000 lbs., and the bridge became heavier with each pull, reaching upwards of 80,000 lbs. Pulling force is a function of how easily the bridge slides on the Hilman rollers and the dead weight of the steel span.
"The launch went as well as we could have imagined," Burchett said, adding, "We encountered a few challenges during the launch related to the small margin for tolerances. On the piers, we only had about a half inch tolerance with each gap. Any lateral movement of the girders or minimal inconsistencies in fabrication of the girders or rollers led to rollers not lining up with the gap in the splice plates. While this cause a bit of delay on the eastbound launch, we modified the splice plates on the westbound bridge that helped reduce the frequency of these issues."
The bridge was listed off the Hilman rollers to allow the bridge to sit on its bearings once the bridge launch was complete.
Reflecting on the bridge launch, Burchett said, "This was the first time a girder launch has ever been performed in Kentucky, and I was glad to be a part of it. We would definitely use the approach again if the conditions called for it. The designer, Stantec, led by David Depp, Engineered Rigging, and the inspectors with KYTC did a great job of working with us to make this happen."
Source: Engineered Rigging