Waffle Slab - Equivalent Average Thickness

[hdp321]

I have to analyze an existing waffle slab and have been looking for the correct procedure to convert my slab and ribs to an equivalent average thickness. CRSI shows a charts, but I need to do a handcalc. The formula CRSI provides has a "tr" variable, which is the equivalent thickness of the rib area. I can't give this out. Can anyone help me?

 

[msquared48]

What do you mean you can't give it out?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[hdp321]

Sorry can't figure this out.... Autocorrect

 

[slickdeals]

Not sure why you would want to convert the waffle slab into equivalent thickness flat slab? The ribs are thicker for a specific reason and modeling the slab without ribs and a shallower equivalent thickness is not comparing apples to apples.

 

[hdp321]

I'm looking to analyse the the slab in RAM Concept, but after looking at it a little closer I think you are correct. Looks like the equivalent thickness should only be used for approximate deflection calculation.

 

[slickdeals]

Not for deflection either. The only use it would have is to calculate effective weight. That's it.

 

[slickdeals]

If you are using Ram Concept, you can model orthogonal beams (waffle ribs) and model the slab on top and design each rib (beam). Essentially it is a two way system.

 

[hdp321]

Slick

CRSI has a procedure to calculate approximate deflections by using a solid slab thickness having the computed equivalent stiffness of the waffle slab. The thickness "te" is computed as the average of the gross moment of inertias of the solid head area and ribbed area.

Thanks for info on RAM Concept