×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Slab-on-grade radiant heat

Slab-on-grade radiant heat

Slab-on-grade radiant heat

(OP)
Has anyone ever done a building basement slab-on-grade with embedded plastic pipes in the bottom half of the slab that provide radiant heating?

Can the slab-on-grade design be the same as if there were no pipes in it -- that is, unreinforced and early-entry sawcut to about 1/4 the slab depth at 4.5 m maximum centres each way? I am concerend about whether the plastic pipes kill some or much of the effectiveness of the sawcuts.

If they do interfere with the effectiveness of the sawcuts, what can be done, without making the slab-on-grade excessively expensive?

The slab is about 70 m square. The plastic pipes are about 16 mm diameter I believe.

RE: Slab-on-grade radiant heat

I did my basement radiant slab by dividing it into 20x20 ft. squares with cold joints and made each area a separate zone for the radiant.
Do not saw cut as you will likely hit the tubing.

RE: Slab-on-grade radiant heat

(OP)
To ExcelEngineering - in my case I suspect that it is too vast an area (> 200 feet square, or 40,000 sq.ft) to be economical to zone into 20 foot square segments, although perhaps not. The sawcuting ought not be a problem because the mechanical engineer proposes a 150 mm (6") deep slab with the piping in the bottom half of the slab; the the piping will be well below the the bottom of the sawcut.

But what I am really interested in, is whether anyone has done large area slab-on-grade with the radant heating piping crossing the sawcuts. Or does anyone have any advice for how this should perform, if the palstic piping crosses the sawcuts?

RE: Slab-on-grade radiant heat

I would expect that the plastic piping may provide some restraint at the control joint locations. How much restraint is difficult to quantify. As long as all parties are informed of the possibility of cracking and willing to accept the possibility of cracking within the panels, it should not be a problem.

RE: Slab-on-grade radiant heat

I haven't done this but my gut feel is that it shouldn't be a problem. The radiant tubing should be much less stiff than the concrete and, therefore, shouldn't affect the cracking behaviour materially.

Are you concerned more with the performance of the slab or potential damage to the radiant tubing?

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Slab-on-grade radiant heat

In my experience the radiant heat tubing has the ability to elongate much more than your concrete crack width will be. Due to this I cannot see it providing enough resistance to change where the concrete will crack.

I would go ahead with your sawcutting as if the heat lines weren't there.

RE: Slab-on-grade radiant heat

It's also not that different from the situation with topping slab systems which we deal with regularly.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Slab-on-grade radiant heat

(OP)
Thanks for your comments. Would you agree that we do not have to put any mesh or rebar in the slab-on-grade, as that would be our standard practice for slab-on-grade on sound soil and not loaded to greater than 100 psf? Thinking of 150 mm thick slab of 25 MPa concrete.

RE: Slab-on-grade radiant heat

The tubing has a tendency to float to the top if not secured properly or often enough.

RE: Slab-on-grade radiant heat

(OP)
Yes right. That requires only a mesh to tie it down to, but we do not need rebar over the piping to control cracking - right?

RE: Slab-on-grade radiant heat

(OP)
To Dbronson - this deals directly with my question and is very helpful indeed. Thank you very much. Much appreciated.

RE: Slab-on-grade radiant heat

(OP)
Do you also happen to know how the pipes are held down against flotation?

And do we need to specify "expansion joints" at some given centres to avoid the possibility that the thermal effect from the embedded pipe heating will exceed the concrete shrinkage, and cause the slab to buckle?

RE: Slab-on-grade radiant heat

In regards to the details -> I have no experience here but from what I recall those tubes are pretty flexible (maybe there are different types of tubing?). I mean more flexible than pvc, but I suppose there is basically no adhesion from pvc to concrete(?). I suppose better safe than sorry (?). But atleast there is a publication to back you up.

EIT
www.HowToEngineer.com

RE: Slab-on-grade radiant heat

(OP)
I expect that the sleeves are needed or they would not have shown them in their typical detail. But on a project 200 feet sqaure, it is a heck of a lot of sleeves to install.

RE: Slab-on-grade radiant heat

I don't believe the radiant heating ever causes enough thermal expansion of the concrete to risk buckling. I have seen these installed in an 8 plex thickened edge slab (roughly 200'x50') using only sawcuts and there was no issues with either cracking outside of the sawcuts nor thermal expansion. And these were installed in an area where the heat is cranked all the time and the outside temperature is well below freezing for the majority of the year (Northern Canada).

RE: Slab-on-grade radiant heat

There's always the danger of vertical movement causing issues in a building. you need to prepare the base material appropriately to limit the amount of movement seen. if you are concerned you could always put in a rebar mat (or mesh but I rarely allow the use of mesh in any of my projects as more often than not it gets trampled during the concrete pour and ends up at the very bottom of the slab removing any effectiveness).

The benefit to adding the mat is you can then tie the radiant heat lines to the mat which will keep them in the bottom of the slab instead of floating to the surface.

RE: Slab-on-grade radiant heat

And back to his original question about the integrity of the slab....

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources