TWO way slab-Two questions

[dgkhan]

1. I have to do rough estimation on an existing flat slab.
It follows DDM in one direction only. Can I analyse one direction using DDM?
and if it fails, no need to check in other direction?
2. What is the load path etc in two way slabs? Some in depth on design basis so that I can make more accurate analysis.

 

[canstructural]

1. Yes. Better do a finite element model like SAFE and see picture as a whole. But make sure use a pattern loading. ADOSS do that too, but it's again one strip at a time.

2. If you are checking flat slab, half the column spacing from either side of grid under consideration is your load on that strip.

 

[etbetz]

If your deck doesn't meet the DDM rules, then you shouldn't use DDM. The equivalent frame method is simple enough with computers these days. Adoss is a great antique program that you may be able to find, i think PCAslab runs around $1200, and of course some of the more expensive programs like safe and adapt can do it.
You can also do it easily with a cheap 2d frame program if you account for the reduced column stiffnesses of an equivalent column per aci section 13.7.4.

 

[samdamon]

There is a description of how to reduce column stiffnesses when using a plane frame analysis program in ACI publication SP-183.