Setting long reinforcing cage for drilled shaft
Setting long reinforcing cage for drilled shaft
(OP)
Can anyone guide me to a source of information or make recommendations on the handling of long, heavy, double, reinforcing cages for drilled shafts? The cages are about 130 feet long and weigh about 700 pounds per foot. The cages have double circular rings of vertical #18 bars with #7 spirals with 3 inch pitch. The inner cage is 40 inch diameter. The outer cage is 60 inch diameter. In addition, the cages will have instrumentation equipment attached inside. The drilled shafts are 72 inch diameter with 74 inch outside diameter steel casings. The drilled shafts are being installed out in the river using barge mounted equipment.





RE: Setting long reinforcing cage for drilled shaft
I'd call and talk to Bill Eisenhower at Ensoft to see if he is aware of anyone that has done this "recently." Or maybe the guys at Fugro's office in Houston; also STS in Chicago - try to get Clyde Baker. He's semi-retired, but I think you can find him through STS.
I've done a 40 foot pier 96 inches in diameter with a single cage of No. 18's and 2.25 inch anchor bolts. It was heavy but short. It still took two cranes and multipoint pickup. The cage used hoops, not spirals, and had lots of wire ties. I'd be worried about the vertical bars shifting "up/down" in the cage because of the spiral. This can happen with hoops, too, but it seems to occur less frequently.
You do have one thing going for you: the double cage. It should provide extra flexural strength during pickup by reducing the likelihood the cage will "egg", collapse and damage the bars. The cross bracing is pretty damn important.
Have you thought about a structural analysis of the pickup?
RE: Setting long reinforcing cage for drilled shaft
RE: Setting long reinforcing cage for drilled shaft
RE: Setting long reinforcing cage for drilled shaft
It looks to me that the bracing will need to be placed between the two cages...
A wild idea: why not use a 36 inch pipe as an "internal mandrel" to help the cage hold its' shape? No bracing inside the inner cage this way. But it will add to the overall pickup weight...
RE: Setting long reinforcing cage for drilled shaft
I agree that multiple cranes and pick points will be needed. I was hoping someone could recommend suitable tilt-up rigging equipment and a supplier.
RE: Setting long reinforcing cage for drilled shaft
You can't rely on ties for handling cages horizontal an vertical reinforcement will have to be welded together at least on a few rows for the bottom and upper parts of each section and the splicing should also be welded.
Hanging bars and positioning bars will have also to be designed and welded carefully. Bracing will be necesary to go from horizontal to vertical position and cut with a torch when the cage is lowered in the pile. You will need at least 350 to 400mm free space to lower the tremie pipe.
It seems very unwise to let this operation carried out by a GC alone if he has not got its own experience of this kind of operation which is not common for a specialized sub-contractor.
Good luck
RE: Setting long reinforcing cage for drilled shaft
RE: Setting long reinforcing cage for drilled shaft
As far as cranes go, the maximum pick may be the rebar cage or it could be the weight of a vibro hammer and temporary casing being pulled during the shaft pour. I don't know what you have. In any case the shaft service crane is always sized to do the job at hand. A 240 ton barged mounted crawler will pick 120,000 lb at 40 ft radius with 160 ft boom and 2 degree list. A 240 ton barge mounted ringer will pick 120,000 lb at 190 ft radius with 260 ft boom and 2 degree list. Use the proper tool for the job.
I'll not get into rigging since anyone qualified to perform this work will know how to do their own rigging.
RE: Setting long reinforcing cage for drilled shaft
Make sure inspectors are watching the cages as they go in. If there is any rupture of the tiewire, have them redo it. If any of the CSL tubes rupture, have them reinstall them. After a few of these problems, the contractor becomes much more willing to take better care of the cage when suspending it.
Also, multi-section cages can work well, but you have to make sure you have the alignment issues undercontrol. Typically, we have used a short lower section (at that time the one loaded with 2 levels of O-cells), so that the splice is really not within an area of "high moment or shear" (I expect that 100 feet down, most of this has been disipated). Let's not use my last comment as a "theoretical discussion maker."
Be ready for some flexure and quantify what is acceptable in the specs. A well written spec makes it much easier to deal with the problems when they arise.
Zdinak
RE: Setting long reinforcing cage for drilled shaft
You said, Let's not use my last comment as a "theoretical discussion maker." Aw, you're no fun!
Actually, I agree with your comment - that's about 14 to 15 diameters below the top of the pier, so it should be well below any areas of "high moment or shear." The only exception might be if the pier is socketed into rock at about that depth.
I'm not surprised your contractor balked at using an "internal mandrel." I made that suggestion with some tepidation; I'm still waiting to see a contractor use one.
RE: Setting long reinforcing cage for drilled shaft
RE: Setting long reinforcing cage for drilled shaft
RE: Setting long reinforcing cage for drilled shaft
RE: Setting long reinforcing cage for drilled shaft
RE: Setting long reinforcing cage for drilled shaft
RE: Setting long reinforcing cage for drilled shaft
Zambo
RE: Setting long reinforcing cage for drilled shaft
RE: Setting long reinforcing cage for drilled shaft