Two Slab Supported by 4 walls
Two Slab Supported by 4 walls
(OP)
What method of analysis would be used when a two way slab is being supported continuously on 4 sides? An example would be a 20'x20' masonry structure with a concrete roof. Due to building limitations, the slab has to be one thickness. I'd assume a two way slab design would be best, but when looking at ACI 318, there is no analysis information when a slab is supported by continuous walls. It seems to only discusses two way slabs for column grids.






RE: Two Slab Supported by 4 walls
For a case you're talking about, model the edges as pinned, do your analysis, and add reinforcing as necessary. For a lot of these, the slabs are designed in one direction and the controlling reinforcing is provided in both directions.
RE: Two Slab Supported by 4 walls
I would just toss it in RAM Concept though...
If you really want to shortcut it... you could design it as one way and put that reinforcing in both directions...
RE: Two Slab Supported by 4 walls
BA
RE: Two Slab Supported by 4 walls
RE: Two Slab Supported by 4 walls
If you want, run another model with three in each direction and take the worst case.
RE: Two Slab Supported by 4 walls
Good Luck
Dik
RE: Two Slab Supported by 4 walls
M* = 0.056FdL2 where Fd is your uniformly distributed design load and L is the slab span. You would need to check deflection also.
RE: Two Slab Supported by 4 walls
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant
RE: Two Slab Supported by 4 walls
BA
RE: Two Slab Supported by 4 walls
Dik
RE: Two Slab Supported by 4 walls
RE: Two Slab Supported by 4 walls
Can you post a complete pdf copy of your mathcad program; I'd like to try to enter it on my pocket calculator. You may not want to, and, I fully understand.
Thanks Dik
RE: Two Slab Supported by 4 walls
I don't understand your request. The rest of the calculation checks beams, columns, and connections for a stair assembly. I don't have any other options in the program other than the (4) I included:
1.) (4) edges simply supported
2.) (2) short edges fixed, (2) long edges simply supported
3.) (2) long edges fixed, (2) short edges simply supported
4.) (4) edges fixed
I have uploaded the actual Mathcad (v15) portion of the Roark's formulas. Nothing was hidden, so all it does is save anyone some typing if they want to use it. Table 11.4 of Roark's 7th Ed. has several other conditions for rectangular plates and loading conditions.
Also, to answer my question earlier about elastic/plastic section modulus; it is the elastic section modulus. Proof is found by taking a/b = infinity for the (4) edges simply supported. We know stress would be equal to M/S or M/Z. With beta=0.75, we find it is equal to M/S. Now you can calculate the maximum moment in the plate instead of stress.
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant
RE: Two Slab Supported by 4 walls
Dik
RE: Two Slab Supported by 4 walls
I would too for steel if I needed it. In my applications, the deflection controls so it doesn't matter if it is elastic or plastic. That is just the way the stress equations are given by Roark's. Knowing now that it is the elastic, I will probably adjust my beta values so that I calculate a moment instead of stress to match the Mn/Ω vs M comparisons of the last (2) releases of the AISC SCM.
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant