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# Civil Engineering/slab design methods

Question
QUESTION: dear sir,
According to my knowledge the methods of analysis to design slabs are:
1.elastic analysis by idealization into strips or beams.
2.semi empirical coefficients as given in the code and
3. yield line theory.

In SAFE software , there are two methods to design slabs
1.strip based design method.
2.FEM based design method.

please explain which method in SAFE relates to method manually , i assume strip based design method is nothing but "elastic analysis by idealization into strips or beams". Am i correct in saying so? and also explain FEM Based design method relates to which method manually ? is it "code based semi empirical coefficients method". please also explain why no software uses yield line theory to design slabs.

thanks

I am assessing about your question , please remeber me one week later. A FEM method is very general and sophisticated method which models the slab as a 2 way plate and a hand calculation whatever to be is an approximation of such a modelling. Then you can compare your hand calculation with the finite element method result and consider it with some 10 to 20% ERROR.  But for the platic method, it is difficult for a software to recognize the yield lines in a general slab geometry. It is needed that the engineer identify them. For more information remember me later please.

Regards
BEH

---------- FOLLOW-UP ----------

QUESTION: Sir,
A Kind reminder about the above problem which you promised you will return back with detailed answer, thanks

Dear Arsalan

Sorry for my late response. A Finite Element Analysis is as you stated a sophisticated method which may have some difficulties about the accuracy of assumptions then it is not as it is belived a more accurate or better saying more reliable method. The engineering methods like strip method which are best fitted with hand calculations are to provide the design with more time consumming and more reliable and more safe solutions. A FEM method is very sensitive to the assumptions and may be accurate if you can provide reliable data. After all I suggest you to check every sophisticated result with handy methods say strip method to get in a good margin of saftey.

Regards
BEH

Civil Engineering

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#### Babak Esmailzadeh Hakimi

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

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