Time for another work blog!
Brenda's company recently completed a new steel girder bridge across the Piscataquis River in Howland, Maine. Now that the new bridge is open, it is time to take down the old steel truss bridge, which is more than 70 years old and covered in lead paint. The old bridge consisted of three identical trusses, and the crews removed the center truss two weeks ago. Brenda was asked to come up and help on Thursday in the effort to remove the second of the three trusses.
Crews had already removed the concrete deck, so all that was left was the steel structure, which weighed about 200 tons per truss.
The plan was to remove each 180 foot truss by jacking it off its supports, then floating it over to shore. From there a big excavator with a giant "shear" on its hydraulic arm would cut the truss up into pieces about 8 feet long, which would then be loaded into trucks and hauled away. This method is used to avoid exposing workers to lead (which is a health hazard), like they would be if they cut it up by hand with torches.
When Brenda got there on Thursday morning, the first truss was almost completely demolished.
Brenda and two other engineers from her group were assigned the job of running the hydraulic jacks to lift the truss off its foundation. Here is her work station, on top of Pier 2, with a little float alongside for extra space. (On a side note, notice how there is no bathroom out there? Yep.)
Here are the hydraulic jacks, one under each corner of the truss. Notice how rusted-out the steel floorbeam is--there was some concern that the beam would crumple up when it was lifted, but luckily it did not. The goal for Thursday was to get the bridge jacked up high enough to slide floats underneath it, which was about two feet higher than it started.
Brenda was assigned to run the hydraulic pump which controlled the jacks on her end, while several crew members handled the blocking. Another engineer from her group was on the other end of the truss with a few more crew members.
The engineer who had designed the jacking system and planned the operation, Bob (in the yellow jacket below), was on Brenda's end and was understandably quite stressed out. His system had worked well on the first truss removal, but this one was a little different, and he had a lot to worry about.
The jacking operation took most of the day (again, remember the lack of a bathroom on the pier?), because the jacks were only capable of lifting about six inches at a time before they had to be reset. The blocking was 3.5 inches tall, so each time the jacks would pick the bridge up about 4 inches, then the guys would slide in another layer of blocking, then Brenda would set the bridge back down on the new support, and the guys would put another layer of blocking under the jacks. Then Brenda would pick the bridge back up, etc., over and over, alternating ends of the truss, until....
....the bridge was sitting about two feet higher (on the log cabin stacks of blocking) than it had been. At this point it was high enough to get the floats underneath it, but there wasn't enough daylight left to do it, so the float-out was put off until the next day.
Friday morning wasn't quite as nice and sunny as Thursday had been, but everyone was motivated to get the work done and nobody complained about the cold. In the morning safety meeting, the Superintendent (Sparky, in the green shirt below) went over the float-out plan in minute detail, while Brenda concentrated on drinking less coffee than the day before.
Out at the bridge Bob checked out all the hydraulics....
...and measured the water level once again to make sure the floats would fit underneath. The project site is just upstream from a dam, so the water level is tightly controlled and the current is very slow.
Finally it was time to start moving the floats into position. Small work boats (known as skiffs) were used to position the two floats....
...which had previously been prepared with timber blocking laid out in the correct position to support the truss.
The floats were eased underneath the bridge....
....and all the final preparations were made....
....then it was time to get back on the jacks. This time the goal was to lower the bridge evenly down onto the floats without causing it to sway sideways or fall off the blocking. Once again Brenda ran the jacks at one end, and everything went pretty smooth (despite Bob's worries).
Finally the jacking was complete, as all four ends of the truss lifted off the supports and the load was taken on to the floats.
At this point the truss was ready to be moved in to shore....
....but Bob and Sparky called one more meeting to go over the plan again, and make sure everyone knew their job.
As you can see from the photo below (taken from the new bridge), it was a pretty tight squeeze to get the truss out from the old piers and slide it back towards the far shore. Everyone knew that the Maine DOT was watching, and any damage to the new bridge would be duly noted.
Here is a view of the shore end of the truss about half slid out, with a few locals watching from behind a barricade...
...and here it is after clearing Pier 2, starting to move towards the far shore.
Sparky knew that the two skiffs alone wouldn't be enough to move the truss across the river, so he used the skiffs to hold it in position against the current, and he used the "Dinny Barge" to move it west. The Dinny is basically a miniature tugboat consisting of a couple of floats tied together with a giant outboard motor and a place for the operator to stand.
The Dinny slowly pulled the big truss across the channel....
....and then gracefully slid out of the way when the water got shallow near the bulkhead.
The last bit of movement into position was accomplished by the two skiffs, with a little help from the on shore crane....
....and under Sparky's watchful eye.
When the truss was finally in position, Bob could finally relax and call it a job well done.
Brenda really enjoyed this operation, and is hopeful that she will get to go back up to Howland for the removal of the third and final truss next week.
