ranawaseem (Civil/Environmental) (OP)
14 Feb 13 2:15
Dear all, Please see the attached image. This formula is suggested to calculate EI of composite section. In my case I have
concrete section of 600x1700mm
4 corner dia 25mm bars assumed
W shape of 1000mm depth and 400mm flange widths with 50mm thickness for flange & web
I calculated the EI eff = 4.86644E+15 N.mm²
Now I want to model in ETABS only the concrete section (original 600x1700)
but with increased EI...For this I can either increase I modifier in ETABS or define a new material for this specific section with E value
I just want to check the deflections (elastic). I dont need ETABS to design this way...
Now my question is: If I want to change only E in material property of this concrete section...
I will be divide EI eff (calculated above)
by I (moment of inertia of concrete section to be modelled in ETABS..and that is
600x1700mm conc column)
So I will get E value which will be used in ETABS material properties...
As you can see in excel sheet snapshot that new value of E is about 50% (0.5) of Ec of concrete...
I mean my Ec was equal to 39323 MPa and my new value for E effective = 19810 MPa only.
Does this makes sense? Is the concept valid? I heard that you need to put E = 2 times the Ec to model a composite column in ETABS..but in my case I have only 0.5 factor...
Please guide me here!
By the way:
Is, As etc are parameters for Steel Section
Ic, Ac etc are parameters for Net Concrete Section
Ig, Ag etc are parameters for Gross Concrete Section
Icr, Acr etc are parameters for Steel Rebar
Ec = modulus of elasticity for concrete = 4700 under the root f prime c
Es = modulus of elasticity for steel = 200 000 MPa