|Rolling. Inspector uses custom-designed device to rappel down bridge cable. (Photo courtesy of Burgess & Niple)|
The five-member inspection team from engineer Burgess & Niple Inc., Columbus, Ohio, used the devices to inspect the cables of the Dames Point Bridges 1,300-ft main span as part of a $125,000 two-year contract. "This was unique due to the fact that we wanted a hands-on inspection of the stay cables," says Scott Hamilton, project manager with the Florida Dept. of Transportation. FDOT plans to repaint the cables of the 25-year-old, 10,645-ft-long bridge and wanted to make make sure there were no deficiencies in the cables, Hamilton says.
B&N designed the device based on bridge plans and site visits, says Mark Bernhardt, director of facility inspection. "Each bridge is unique, so there was no off-the-shelf stuff to use," he says. "We used an in-house design competition for people to come up with ideas."
Of three tested prototypes, the team chose a design constructed with parts obtained from hardware and outdoor equipment stores. Device weight was a major factor since inspectors would have to carry equipment up ladders to the tops of the 300-ft towers. In addition to the customized rolling devices, B&N engineers designed specialized rigging plates and connection hardware to provide anchorage points at the tower tops for load and safety lines.
B&N inspectors used 600-ft ropes to rappel to the deck. "With the harness, youre carrying about 70 pounds," says Ray Stokes, the firms transportation business development director. The inspectors also had to be wary of high winds and hurricane season during the three-week inspection process. They checked the bundles of strands covered by 7-in.-dia steel pipe coverings and found no significant deterioration.
Since the firm began specializing in the niche in the 1970s, it has performed 10,000 bridge inspections, says Stokes. The 20-member climbing crew has revised and updated techniques and trained some 400 state bridge inspectors and railroad workers.sing a new custom-designed rolling device, bridge climbing specialists last month completed the first hands-on inspection of a Florida bridges cables in preparation for maintenance.