Concrete Expansion due to temperature....

I'm trying to find some "allowable expansion" values/formulas for the expansion of a monolithic concrete slab due to temperature differential (something along the lines of "movement due to expansion exceeding "x" will cause damage to non-structural elements attached to the slab"). I have never seen this concept covered in the ACI code. Any help is much appreciated.

My AISC 13th edition says that it is 0.00055 (per 100 deg F). (for total expansion)

I honestly never encountered this myself for concrete specifically, but I do know that the MSJC's and AISC's thermal expansion for masonry do not agree. (for total expansion)

For allowable expansion, I'd consult IBC/ASCE for thermal "deflection limits."

:2cents: :dunno:

Edit: Why didn't I think about this earlier.....

First of all, for thermal stress to occur, the slab must have a rigid boarder on each end. (otherwise, it could expand and no stress would be imposed) If stress would occur, I'd equate the imposed strain in the expanded concrete to the modulus of rupture of concrete. I'd give myself a nice factor of safety too!

do you mean during initial cure or during it's service life? Often times "expansion joints" are incorproated to take care of service life expansion. You could get some initial growth from the heat of hydration during mass pours. Need more information to answer this one.

Lastly search through the ACI Manual of Practice to see if your situation is covered. Good luck.

kevo_55 said:

My AISC 13th edition says that it is 0.00055 (per 100 deg F). (for total expansion)
I honestly never encountered this myself for concrete specifically, but I do know that the MSJC's and AISC's thermal expansion for masonry do not agree. (for total expansion)

For allowable expansion, I'd consult IBC/ASCE for thermal "deflection limits."

:2cents: :dunno:

Edit: Why didn't I think about this earlier.....

First of all, for thermal stress to occur, the slab must have a rigid boarder on each end. (otherwise, it could expand and no stress would be imposed) If stress would occur, I'd equate the imposed strain in the expanded concrete to the modulus of rupture of concrete. I'd give myself a nice factor of safety too!

Click to expand...

A contractor I do business with is building a 3-story office building. The exterior walls were CMU bearing walls and the floors were concrete slabs poured on cold form deck on top of steel joists. Expansion joints were not provided. The floor slab is about 180 ft by 40 ft. After pouring, cracks started to develop in the CMU walls at the connection to the joists (connection consisted of an anchor bolted connection between steel floor joists and CMU wall. In my opinion, a likely cause is expansion due to day/night temperature variations in the floor slab concrete. I'm just trying to find some allowable tolerances for such expansions. Thank you for your time.

Preparation Hell said:

A contractor I do business with is building a 3-story office building. The exterior walls were CMU bearing walls and the floors were concrete slabs poured on cold form deck on top of steel joists. Expansion joints were not provided. The floor slab is about 180 ft by 40 ft. After pouring, cracks started to develop in the CMU walls at the connection to the joists (connection consisted of an anchor bolted connection between steel floor joists and CMU wall. In my opinion, a likely cause is expansion due to day/night temperature variations in the floor slab concrete. I'm just trying to find some allowable tolerances for such expansions. Thank you for your time.

Click to expand...

Differential movement between your bearing walls and the steel structural frame should have accounted for in the connections. Sounds like a bad design. Based on your description I'd say the movement is in the steel joists not the floor slabs (which I bet have made thier own expansion joints (i.e. cracked) by now.)

I don't know of any allowable value for expansion. I'm not sure where it would say it, but I am sure the code says that the overall design needs to be able to safely handle stress due to expansion/contraction as well as the overall expansion / contraction of concrete should not adversely affect the function of the building or its fixtures.

Sorry I couldn't be more helpful.

I will look at it in more depth when I review concrete again.

Wimp :dunno: