Civil Engineering/Ribbed slab


Dear sir, What is the difference between ribbed slab and waffle slab.
what will be the difference if we model the ribbed and waffle slab as a normal slab beam instead of using the rib slab section directly from the database of ETABS.
I modelled the grid slab of 15m x8m in etabs as normal slab beam of spacing 2.0179x2.063 in two perpendicular direction .I designed the same grid slab manually by using plate theory. The value of rebar is very high in manual design than in Etabs. Which one should i follow? Whether i have to model as a rib slab as available in section database of Etabs?

Thanking You!

Dear Niranjan

Waffle slab is a two way slab with centered reinforcement in rc beams. Ribbed one is one way slab.  I Dont belive that your manual way to consider a flat slab is in escence different than what etabs does. I think a mistake is in the air , may be your load factors or strenghts . Check them again and let me know.


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Babak Esmailzadeh Hakimi


I can answer questions in Structural Engineering, Earthquake Engineering, Project Management and Project Control topics!


I am experienced in the area of earthquake engineering in electrical power industry, i.e. Lifeline Earthquake Engineering. My focus has been on structural seismic design of power installations. Recently I have got involved in project management in the category of constructional engineering.

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Bs degree in Civil Engineering from Ferdowsi University ,1988, Mashhad Iran, Ms degree in Earthquake Engineering, Sharif University of Technology, 1993, Tehran, Iran

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