EFM for concrete waffle slabs

[ash060]

I am currently doing a lateral analysis for an existing structure that uses a two-way waffle slab system with drop panels over the columns. It appears to be the only lateral force resisting system for the building which is about 50-yrs old. I do have drawings that show reinforcing and member sizes.

My question is how do you model the waffle slab as a slab-beam member using equal. frame?

Do you use the total I for the whole slab width or something else?

Should I have two different I's for the slab beam one in the drop panel area and one in the waffle area?

The waffle joists are 3'-0" c/c E.W. they are 6"x14" with 2 #5 bottom and stirrups at 6" c/c. The slab is 4" deep. It use a CRSI Dome system which i am not familiar with.

The columns are 16x16 with 8#9 and spaced at 27' c/c E.W. Just a big box. Seismic is not an issue only wind.

Any help would be great.

 

[JAE]

ACI section 13.7 discusses this a bit. Have you looked there?

 

[rapt]

ash060,

2 different inertias, like a flat slab with drop panels, except in this case you flat slab is a T section.

 

[ash060]

Rapt

the joists are 3' c/c which is much closer than my strip width. Do I use a waffle type section for when I calculate inertias?

 

[hokie66]

For lateral analysis, I don't think it is appropriate to use a slab width any wider than the drop panel. So you would just use the sum of the rib widths which occur in the width of the solid section for your moment of inertia between drops. So if your drop panel is 12'6" wide with 5 ribs in that width, you would use 2'6" as the tee web width between the drops, and 12'6" as the flange width.

I think the 16" columns will be the controlling factor.