Cable Stay Bridge Inspection

Last October I was part of a cable stay bridge inspection in Boston, MA. While I was away in Kentucky inspecting, the rest of my office was busy inspecting the underside and beginning the lower section of the piers and cables.

After I arrived home I had a day off and I began my part of inspecting the upper portion of the pier towers and cables which reached heights of 270 feet over the roadway. Since equipment could not efficiently inspect that high we used SPRAT climbers (myself and other guy from PA). We started by carrying over 1,000 feet of rope to the top of the north tower and rigging up our lines and rescue lines. That night we began to inspect the northern cables. With limited hours (11pm to 3am) we had little time to inspect since we were not allowed to enter the towers until lane closures were out. The first few nights were mainly learning what was the most efficient way to climb. The limiting factor for this bridge was our need for night work and thus lane closures. Luckily for us weather was good and winds were calm (less than 10 mph most nights).

As far as how we climbed, for the concrete pier towers we were able to climb out of the top at the aviation beacon and descend to the portion that was inspected by man-lifts and then ascend back up to the beacon. The first few nights we tried different ways such as ascending from a man-lift about 110 feet above the roadway (figured out that we can climb faster than a man-lift). Next we tried rope to rope transfers from the access vent located about 130 feet over the roadway. This was fast but each night we had to tie off the ropes which led to us ending almost an hour early for this.

For inspecting the cables we started off just like we did before from the aviation beacon but we carried a pair for rollers which were used to hold us ear the cables. This allowed us to stay within an arms reach of the cable we were rolling on and allowed us to see the cable below us. When we were low enough we exited the cable onto a man-lift which was waiting for us. Most nights we inspected 6 cables, we originally thought we could inspect more each night but due to less time each night we weren't able to inspect the 9 we thought we would be able to.

Continuous Prestressed Post-tensioned Segmental Concrete Box Girders

Last week we inspected four ramps in Boston and Cambridge Mass near Leverett Circle and the Boston Sand and Gravel.

The ramps take traffic from the Tobin Bridge to I-93, Zakim BridgeLeonard P. Zakim Bunker Hill Memorial Bridge, Leverett Circle or Storrow Drive. The ramps consist of continuous prestressed post-tensioned segmental concrete box girders.

To inspect the exterior of the box girders an 80' man lift was used since most of the structures were no accessible with smaller lifts due to on going construction and a park. The exterior inspection consisted of visually inspecting the box girders, piers and measuring the bearings for movement.

The interior of the box girders were inspected with three man teams since they are considered a confined space. When inside the box girder the inspection team needs an air meter, rescue air tank and radio, luckily we have only had to carry these once down the interior since there is a hatch at both ends. The interior inspection consisted of visually inspecting (even though we were always within an arms reach)the box girders even though we were always within an arms reach, utilities and measuring the pintle slots for movement.