2-Way Flat Plate Based on ACI Direct Design Method 3

[StructuralAddict]

Hi All,

With reference to the attached floor plan, I GREATLY APPRECIATE it if someone will be so kind to divide the flat plate into "Column Strips" in both E-W and N-S directions based on ACI 318-14 Direct Design Method.

The following are not clear to me when creating the "Column Strips":
1- How to deal with Cores and Shear Walls?
2- How to deal with openings?
3- Does the width of the Column Strip change along a specific column line if (l1) changes?

It would be great to solve this once and for all if someone draws the column strips on the attached sketch.. This will solve it once and for all!

Thank you very much!

 

[r13]

IMO, DDM only is applicable to the area bounded by grids A-E and 4-7. The opening in the middle prevented the applicability of DDM, which requires 3 continuous spans in direction of analysis. You might have to use equivalent frame method instead.

 

[BAretired]

It will never be solved once and for all. Considerable engineering judgment is required in every case.

BA

 

[ATSE]

Strictly, you cannot use DDM to design the entire floor plate.
However, practically, engineers do use DDM for a slab with irregularities and discontinuities.
Parallel walls are treated like very stiff beams in the CS. Oversized opngs (crossing CS and MS) are treated like free edges.
Just about any FEA program (but especially SAFE) will quickly confirm and correct your first pass thickness and reinf sizing using DDM.

 

[StructuralAddict]

Thank you very much. I think it would be more convenient to use SAFE or similar software to design two-way RC slabs. In most buildings, we have openings, shear walls, shifted columns, etc., which make satisfying all the requirements of DDM a difficult task to achieve.

 

[r13]

DDM is the simplest method for two way slab design, it is also the most restrictive on geometric layout. Design software is the choice these days, but there are other hand calculation methods if computer is not available, just more tedious.