Split Sonotube to Install Around In-Place Bar? 2

[soiset]

I'm trying to figure a way to install piers between a reinforced concrete grade beam above, and competent rock below. Reinforcing for the pier will be a single number 9 bar, doweled into the existing grade beam. After the bar is in place, I will have to put the sonotube around it, and the only way I can imagine to do that, is to cut a lengthwise seam in the tube, slip it around the rebar, and then stitch the seam back together.

Has anyone seen this done? Any suggestions on ways to securely close the seam? I'm considering some kind of bands or zip ties, possibly combined with polyurethane adhesive or heavy staples.

 

[Ron]

Routinely done. Use large zip ties (space them every couple of inches for first foot or so) or steel bands (strapping bands). This is all assuming your sonotube is no longer than about 4 or 5 feet and a diameter of no more than 8 to 12 inches. You will need 4' long zip ties.

Duct tape the inside of the seam.

 

[soiset]

Thanks, Ron. The piers will be 6' long, 12" diameter. Duct tape the inside(?) That would be impossible, I think.

Where have you seen this method used?

 

[RHTPE]

What diameter tube are you anticipating? How are you going to get concrete into it underneath the grade beam?

Ron's method makes sense for a small diameter tube (say 6"), but as the tube gets larger, the method gets riskier. If exposure to moisture between installation and concrete placement is very likely, you might consider using PVC pipe instead.


Ralph
Structures Consulting
Northeast USA

 

[soiset]

Hi Ralph. The form diameter is 12". The grade beam is 10", and the excess width of the pier will be toward the exterior, which will facilitate pouring from above, with some cutting on the top of the form and a make-shift funnel. I ran the hoop stress numbers, and can manage using 175 lb capacity zip ties, at prescribed spacing.

 

[RHTPE]

soiset Watch out for moisture issues. Form tubes can deal with a limited amount of exposure to water (after all, the concrete is wet), but too much exposure before placing concrete will weaken them.

I think you could have an issue with reliable consolidation of the concrete underneath the grade beam. You might consider stopping the pier concrete an inch or so short of the bottom of the grade beam. Consolidate well, let the concrete cure a bit, then dry-pack the space with a very stiff non-shrink grount.

Or use a self-consolidating mix if available and fill your 'funnel' well above the bottom of the grade beam. Provide a sealable hole in the form tube on the opposite side from the 'funnel' to facilitate the concrete's ability to push out any air.


Ralph
Structures Consulting
Northeast USA

 

[soiset]

Consolidation at the top of the pier, below the beam, is definitely an issue to deal with. I'll consider your suggestions.

 

[dik]

I've used Ron's method with metal banding and it works well. I've used drywall screws to hold 2x4 'strapping' in place with the first ones set from the inside of the sonotube, while it's horizontal on site and the opposing screws about 1/4-1/2" longer than the thickness of a 2x4 plus the thickness of the sonotube. These are screwed from the outside and project into the concrete a tad. I've used 16" dia, but 12" will likely work (16 has a little thicker sonotube.

I've not used duct tape, but I've seen 4 or 6 mil plastic 'socks' placed in the sonotube to provide a smoothe surface. These can likely be held in place with a staplegun at the top.

If bearing is an issue, the space at the top of the sonotube is used as a sprue to get the concrete in with the help of a small plywood chute and then drypack the space between the gradebeam and the top of the pile.

Dik

 

[TXStructural]

Look into fabric forms (fab-form.com sells a fabric tube that does this exact thing.)

 

[soiset]

dik, I had to look up "sprue." Ralph, I like your idea of stopping the pour short of the top, and using a self-consolidating concrete for the rest. The amounts would be small, probably mixed in a bucket, and added after the regular concrete had begun to set (maybe an hour).

 

[TXStructural]

Why would you wait until the remaining concrete has set? Place the initial lift(s) of concrete and once you reach the top, add whatever mix you desire to help with consolidation. You will not be mixing true SCC in a bucket, so I would probably simply use a moderate dose of polycarboxylate and keep the wcm in the low to moderate range for the entire pour, which will help the material to consolidate with minimal vibration, and would keep shrinkage down.

If you plan to use normal, plant-run concrete, you may need to hold back the initial placement from the top and fill the gap after shrinkage. If you control shrinkage in the mix design and settlement in the foundation, you may be able to place all of the concrete at once, but you should probably plan on filling a gap a few days, or longer, after the pour.

 

[hokie66]

TX,
The gap is left to allow for plastic settlement, not shrinkage. The same reason you don't cast a floor with the columns below.

 

[TXStructural]

Hokie, yes, as I said "you should plan on filling a gap in a few days, or longer, after the pour." My concern was that waiting only until initial set ("maybe an hour") was not adequate. Although, on a 6 foot tall column, I'm sure the gap due to settlement and shrinkage (of all kinds) would be small.