Sunday, April 15, 2018

Removing a tower crane with a GMK5275 mobile crane

(The photos on this page are licensed "CC BY," which means you can copy them freely as long as you acknowledge Dennis DeBruler as the photographer. As a courtesy, If you use some of the photos, I ask that you send me a copy/link/reference of where they were used to bruler <capital 2> xnet <period> <three letter "word" that means commercial>.)

I took over 400 photos, if you are interested in details, most of them are available in a construction trip report. You can use the timestamps to find the related photos.

The Grove GMK5275 mobile crane arrived at 5:06:30  Note the boom dolly. This crane has a telescopic boom. The lattice work you see is a "jib" carried on the side of the boom. They used a jib on the Downers Grove High School job. But they didn't need it for this job, which makes crane assembly and disassembly go faster.
20180408 0329,  ISO 6400
They are lifting the stack of four heavy-duty outrigger pads by hooking onto the bottom pad. Note the outrigger that is partially extended and is using just the builtin pad. This provides enough support when the crane doesn't have any counterweights and is using just a short boom length.

The worker between the two pairs of wheels has raised the pad, extended the outrigger, and lowered the pad onto the heavy-duty pad. The worker on the right is putting a pin back into the outrigger to hold it in the extended position.

Then they built a 51-ton stack of counterweights on the truck bed and hydraulic rams were lowered into the stack to attach to a couple of pillars on the base counterweight to lift the stack up to the crane's "rear end."

After changing from a two-part block with a fairly large hook to a small hook, the boom started extending at 6:31:18. At 6:41:42, all six extensions were out and the boom was at its full length of 223 feet. A boom segment takes a little over a half-minute to be extended. But there is a pause of over a minute between each extension.

06:47:36  They picked up some rigging that had four chains and removed all but one of the counterweights from the tower crane. While the weights were being removed, another worker went out on the boom to attach guide ropes at both ends.
07:35:09  After all but one counterweight was removed, they turned the tower crane around so that they could fasten the rigging to the boom.

One thing to note in the video below is that a worker on the roof was handling a rope at the other end of the boom. At 0:40, he arrives at the edge of the roof. (Just to the right of the tall traffic light.) At 1:20, he throws the bag over the side so that a ground worker can be ready when the end of the boom goes past the edge of the roof. My camera does HD, and, in a new window where you can go full screen, you can see the bag fall against the white backdrop of the building. You can even hear the "thunk" when it hits the ground.

(new window)

08:14:50  After removing the final counterweight, they removed the cab.

08:54:25  They then removed the frame and turret.

09:09:51  The tower consisted of three 39-foot truss segments. These were the tower parts that required the highest boom clearance and longest radius for the mobile crane. This time stamp is for the first segment that was removed.

10:28:17  They then divided the boom into segments.
11:07:08  It is a big deal for the village to grant the contractor permission to close a street. So while they had Maple Avenue closed and a mobile crane set up, the Custom Service Crane crew shared the crane with a Creative Erectors crew.  Creative Erectors is the subcontractor that built the interior of the three-story parking garage using precast concrete columns, beams, and slabs. In the details, I provide a couple of photos from this summer to give context for what they do. Here we see the 223' foot boom being laid out to pick up a slab that was stored on the far side of the building. Not only did this lift have a long radius, the boom was rather close to the top of the building by the time they got it low enough for the hook to reach the far side of the building.

11:17:22  The slab is on it way to the north side of the building to help fill the hole left by the tower's removal.

11:12:30  The first load to leave had the three tower segments, one boom segment, and the cab.
11:49:59  The second load had the frame separated from the turret so that the turret could stand straight on the trailer. In front is the platform that was on top of the cab. In that platform is the power cable that ran up the side of the tower. In the middle is all of the counterweights. Sticking out from the turret at the back is the frame that holds the travelling carrier and laying on the trailer is the block and hook. They had finished loading this trailer before they let the Creative Erectors crew use the crane. But it takes a while to strap everything down before they can leave.

13:07:40  The third, and final, load consists of the remaining boom segments and a trash bin.

Of interest is that there are two test weights in the trash bin. I assume the 2404 pound weight would be lifted with the travelling carrier at the end of the boom to verify the overload alarm did not sound. The tip of the tower crane is rated for 2404 pounds. Then the 245 pound weight would be added to verify the alarm does sound if trying to pick about 10% more than the rated load.

Also of interest, because the boom is triangular, the middle segment was turned upside down and strapped to the first segment loaded on the trailer. You can see the details for the turning and strapping of the middle segment.

No comments:

Post a Comment