Two-Way Slab...Strip Widths??

[DMWWEngr]

Reviewing two-way slab design and I'm having trouble figuring out exactly how to calculate the strip widths. I'm looking at an example problem. It is a "flat" two-way slab. Spans 26' in one direction and spans 22' in the other. Round column capital of 5.5' (from a 2' column)....NO drop panels!! The example is using the DDM procedure. The strips are given in the example but I'm a little "fuzzy" on how to calculate them. My questions are....

1) How does one calculate the width of the column strip and middle strip for a two-way slab??

2) Is there a section in ACI that discusses it that I'm overlooking??

TIA!! ---
Andrew

 

[Ingenuity]

DMWWEngr,

Given you have expressed the dimensions in US units I presume you are dealing with ACI318, if so then you can refer to section 13. DDM is covered in 13.6.

Basically, the column strip width is 50% of the lesser span. Actually, ACI318 also talks about "half" column strips, so it says lesser of 0.25L1 or 0.25L2 on each side of the column. The middle strip is the remaining strip bounded by the adjacent column strips. See 13.2

You also need to check that you comply with the limitation of the Direct Design Method (see 13.6.1) like panel ratio, adjacent spans ratio, LL/DL ratio etc. If you do not comply, use the Equivalent Frame Method. I seldom use the DDM.


HTH

 

[Ingenuity]

DMWWEngr,

Forgive me - of course you are dealing with ACI - you stated it in Q2 and we are in the "ACI concrete" forum. Sorry, I thought i was in the "Structutal" forum.

 

[DMWWEngr]

Thanks for your response!! I knew I was just overlooking it!!

Thanks again, ---
Andrew