Radiant slab and interior LW CMU walls

[jranderson]

Hello all. I am currently working on a project with a radiant slab installation. The mechanical engineer is wanting to use a reflective radiant barrier (bubble wrap/foil/bubble wrap) directly under the slab that has an overall thickness of 3/8". We are looking to use an 8" thick slab, reinforced with #5's @ 18"o.c. each way. The kicker here is that we have interior non-load bearing lightweight cmu walls, 10'-0" tall, that will bear directly on the 8" slab. Our fear is that with the possible compressions of the radiant barrier, which the manufacture says is not a concern, we will get differential settlement possible at the cmu wall locations and the unloaded interior slab locations. My question is if anyone has had any experience with this type application or any references or recommendations on the topic.

Thank you.

 

[concretemasonry]

If you really think about it, the are two points.

1. The difference between lightweight and normal weight CMU have minor differences in wall weight.

2. A wall laid in running bond does actually function as a beam, distributing the loads over a much larger area along the length that reduces deflection of a slab it bears on.

If the block are laid in stack bond, the benefit is reduced.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[shobroco]

Try analysing the load from a 10' high partition on an 8" reinforced slab & see if you are still concerned. If your occupancy requires that kind of slab, the partition load is the least significant thing you'll see. I wouldn't worry about it on a 6" unreinforced slab on a good base.

 

[JAE]

I would think you could take the wall load and spread it out at a minimum 45 degree angle from the base of wall. So for an 8" thick wall, with an 8" thick slab, at a minimum you'd have a spread of 8" + (2)(8) = 24" width of slab inducing pressure on your bubble wrap. With the reinforcing, you might even go to 30 degrees off the horizontal and get more. Take the weight of the wall and spread this over that width (per foot of wall) and then compare with the bubble wrap maximum pressure. You might even do a small load test on a bubble wrap sample to verify.

Dick - not trying to pick on you but whether stack or running bond, the bubble wrap would essentially see the same load. What you are referring to is that with running bond, any soft spots along the wall length would be somewhat better bridged by the wall stiffness. With a uniform subbase stiffness, there would be no difference in pressure.

 

[concretemasonry]

I missed the fact that the wall is bearing uniformly on the floor slab and somehow I was thinking about some other post where the wall was perpendicular to a pvc pipe below the slab.

I also erred when I used old term of "stack bond" instead of the correct term, which is "other than running bond" that is now used in ACI 530 to give definition and clarify various bonding patterns that may not be "running bond", which may be changed in the future.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.