Barn - concrete opinions?

[bebster]

I agree with the rebar thoughts. After consulting with the engineers, I went with a 6" slab (could have been 5") with #3 (3/8") rebar 18" on centers. It's not that expensive, and you can tie them off with plastic cable ties you can get at HD. HD around here sells 1/2" rebar. Put the rebar up on cement bricks to keep it off the ground. (see photo) I'd stay away from the mess -- it gets trampled down to the base and can't add that much value as a result.

I'd slope the entrance down a bit so that the thickness becomes an extra inch of concrete there since that will take the most force with a vehicle driving over the edge.

 

[Brad_Blazer]

I agree with putting a grade beam at least across the entrance. The rebar wire ties go on with a swivel hook tool probably quicker than zip-ties. A metal supplier will be a lot less expensive than big box.
My 40x40 steel building has re-bar in the grade beams and column supports and wire mesh in the floor. The column anchors are also tied across the slab with "hairpins" - re-bar bent in a "V". I made long handled hooks to pull up on the mesh as we went to imbed it. The engineer who designed my slab said it is most effective near the bottom as long as it is imbedded.
The most interesting part of the design for 100mph winds is that a 5000lb UPWARD force is a lot more challenging than a larger downforce. (5000lb is a lot of concrete!)
Anyhow its doing fine after 2 1/2 years. I have some pics in Yahoo:
http://pg.photos.yahoo.com/ph/blazerboy_4/album?.dir=ff22&.src=ph&store=&prodid=&.done=http%3a//photos.yahoo.com/ph//my_photos
Thats me in the stylish boots. /forums/images/graemlins/cool.gif
There is a good detail of an anchor template in place.
I did the pour myself (w/ friends!) and am pretty happy with it although it is not as flat as the pros would get it.
When you have yor slab poured, watch and help all they will let you - its a handy skill to pick up!

 

[Currmudgeon]

</font><font color="blue" class="small">( After talking to the barn design engineer more, I'm convinced they recommend hilti bolts because they worry wet embedded might not get the precision needed. I'm working on the theory that wet embedded anchors (at least on the wall columns) will increase the pullout strength significantly...and I live in a high wind area (90mph rated). )</font>

Mis-located anchor bolts is one of the more common headaches, even when pros do the work. It's really hard to adjust a mis-located anchor. Often we would require custom column bases to be fabbed, as we don't like to see the holes reamed much.

You might check the masonry anchor literature to find out what the pull-out strength of the drill-ins is. It may surprise you. For a four bolt anchor plate, I'd expect the concrete to fail before the anchors rip out.

If you're using cast-in-place anchors, be careful of their placement. Use a plywood template to get the spacing right.

There is an accessory you can get for casting anchor bolts, that leaves a little pocket in the concrete at the top of the anchor. This gives the anchor bolts someplace to bend when you must adjust them with a sledgehammer. They can save your arse. You might be able to improvise something from plastic shot glasses and/or styrofoam. After the concrete is set, you clear out the pockets, bend the anchors with a sledge if necessary, set the columns level with double nuts, and then grout a pad under the baseplates, filling the pockets with grout in the process.

Setting your columns bases on nuts and grouting under them gives you better level control than you can easily get on a slab top.

 

[Ray_H]

Bebster,
What did you use for insulation under that slab and what are you using for a boiler?
Ray

 

[RichT]

Brad, you have a PM
thx
rich

 

[bebster]

I used a product called Insultarp . It's 1/2" thick, and 5 layers that provides vapor barrier and R10 insulation. Rolls right down in 6' or 12' wide rolls. About $500 for a 12x50 roll.

As for a boiler, I'm going with a Viessmann combi boiler that will give me tankless hot water.

 

[drm]

Rich,

From an engineer that consulted for several precast manufactures, let the barn people install the hiltis. Unless you use a transit or total station, and are proficient at it, you will not get the anchors located exactly. Got paid lots to trouble shoot the "pros" when they mislocated them. If you set the anchors they must extend 16 or more inched into the pier depending on the reinforcing size you use in the pier.

You will need much more vertical bars and ties (“hoops”) in the piers. Code would dictate 10 - #6 (3/4" diameter) rebar to consider the pier "reinforced". Check with the barn engineer if the piers need to be reinforced and get the size and quantity from him. As mentioned, uplift on a barn is more often a bigger problem and you need steel to transfer the force from the anchor bolts to the concrete.

Like others, mesh is very difficult to place correctly and rebar is much better. If you insist on mesh put it up on the precast blocks and space 1 1/2” to 2” max from the TOP of slab.

 

[RichT]

drm, I appreciate your input. The barn engr told me no steel reinforcement is required in the piers and none is indicated on the plans. I'll do it anyway. I followed your logic until the part about transferring the load from the anchors to the concrete. Seems like the only way to do this would be to preset the anchors, or at least a portion of them, and tie them to the rebar framework. There is no way to tie the hiltis to the rebar. What am I missing here?

 

[drm]

The Hilti bolts will transfer force (We will talk about tension in this case caused by uplift of the building from wind) to the concrete. The concrete will fail by pulling out a "chunk" of concrete shaped like an upside down cone starting near the end of the Hilti bolt and getting wider at a 45 degree angle to the top of the concrete pier. If the effective depth of the Hilti bolt was 6" then the diameter of the cone at the top of the pier would be 12".

To transfer the load from the Hilti bolt to the whole pier you need to have steel reinforcing adjacent to each bolt located within the failure cone of the Hilti bolt. The rebars will need to have 90 degree hooks at the top facilitate the load transfer. So when the Hilti bolt pulls up it engages the concrete which will then transfer the force to the adjacent rebar. The sizing, spacing, hook, etc. all need to be designed based on the actual loading of your individual case. Since the building engineer has stated that you do not need reinforcing, then this reinforcing evidently is not required. The forces must be small enough.

Lateral (shear) forces must also be transferred to the concrete and if required reinforcing steel. They also are evidently not required.

That being said, I would still provide a minimum amount of reinforcing of at least 6 - #5 rebar. Locate the bars around the perimeter of the pier 2 1/2" in from the edge of the sonotube. With 6 bars they would be approximately 12" apart. I would also use #4 rebar hoops around them with a 20" outside diameter. Tie the vertical (#5) bars to the hoops then place the assembly into the sonotube. Use spacers to maintain the 2” between the outside of the hoops and the sonotube. Place two hoops at the top of the #5 bars and then at 12" to 16" spacing down from there. Be careful that you locate the bars so they will not interfere with the future placement of the Hilti bolts. If they do the contractor will need to have a concrete coring company cut through the rebars. This will cost several hundred dollars.

This may be overkill for your situation but being an engineer I like to see a minimum amount of steel to tie the concrete together. I have seen a lot of damaged foundations that were not constructed correctly. The proper placement of even a small amount of reinforcing will make the pier substantially stronger.

Hope this helps to clear things up a little. Let me know if you have any additional questions.

I hate to do this but in today’s litigious society I have to warn that this is generic information not an actual engineering design. Any design must be performed by a competent professional engineer registered in the jurisdiction of the project.

 

[bugstruck]

DRM, As a former base building Superintendent I always depended on you guys to get the Structure right. Occasionally I'd throw an idea out that made some sense and we'd tweak a design a little and on rare occasion where the Engineer missed something, allot. Most often though, I was the one missing something. I think the metal building engineers (no steel in the piers), in this instance, are planning more from the piers in the bearing than uplift mode. They must be or they are in far left field. Although, even if they aren't needing those piers for anchorage and I don't know how that would be, at say 1500 lbs. each (if I did it right) they are a real good opportunity for some added ballast and his wind speeds are rather substantial. We both know the steel doesn't hurt on the bearing capability either although at 24" diameter I can't imagine that's a serious issue if he has good/stable soils and no serious seismic activity.

Come to think of it, based on his hard clay description and the idea that he may not get much in the way of frost, I can only suppose (no steel) they are trying to get bearing into virgin soil with those piers as designed?? They seem awful deep for an area with little frost though, assuming no backfill to penetrate. If his site were tabletop undisturbed soil, simply removing the topsoil and running a shallow perimeter monolithic turn-down (haunched and expanded a little additional at the main column load points) would seem a better total strength and ballast solution. Admittedly, not knowing the area and without drawings, I'm speculating awfully far and wide. Not that Rich would want to cough up the design costs though, even if it was a workable design.

Rich, I don't know what you did to deserve this, but in the few months I've been up here this is the best string of advice I've seen on any Project thread topic. Real capable group responding and a bona fide Structural Engineer to boot. /forums/images/graemlins/wink.gif

Almost forgot, you will get a more accurate (level) slab if you have a screed form or two. You can do them as metal permanent which creates the score (fracture) lines, or wood/pipe temporary. Remember to pitch or pocket the slab at the garage doors for drainage away during rain. Nothing will have you cursing more than that little oversight.

Best of Luck /forums/images/graemlins/grin.gif