ETABS

[DamirDz]

Hi all!

I didn't know where to place this q, so i thought it would be most appropriate here.

Does anyone know if Eurocode defines any stiffnes modifiers for members?
I am mostly intersted in the stiffnes of critical sections (plastic hinges) in members.

Or is this all covered by the behaviour factors?

Tnx

[DamirDz]

Hi!
I have some more questions...

When we are performing a modal analysis (and then seismic) we asume that the slab is absolutely rigid for flexure.

So my q's are:

How do we model this in ETABS?

Do we model the slab as shell and then assign the rigid diaphragm option? or

Do we model the slab as membrane?

Another q is about modeling the slab as membrane:

I performed an analysis and still had bending in the slab. How can this be and what have i done wrong (if i did ;P )?

Tnx in advance

[iceman84]

The slab can be modelled as shell if you want to find the efforts in the slab and as membrane if you want to find the efforts in the beams, walls or columns.

[DamirDz]

The slab can be modelled as shell if you want to find the efforts in the slab and as membrane if you want to find the efforts in the beams, walls or columns.

Tnx for your reply, but that i already know. But I would like answers for my q's if someone care to explain.

Tnx

[tuanna]

The slab can be modelled as shell if you want to find the efforts in the slab and as membrane if you want to find the efforts in the beams, walls or columns.

Tnx for your reply, but that i already know. But I would like answers for my q's if someone care to explain.

Tnx

Dear DamirDz,

Always apply Rigid Diaphragm for each story level whether your slab is modeled as Membrane or Shell. But, if your slab is a thin element which would not act as an diaphragm action (for example non-concrete slab like Trapezoidal form Steel Sheet roof in an Industrial type structure ( as you know we use brace elements for stability) ), don't assign Rigid Diaphragm.

Regards

[DamirDz]

Dear DamirDz,

Always apply Rigid Diaphragm for each story level whether your slab is modeled as Membrane or Shell. But, if your slab is a thin element which would not act as an diaphragm action (for example non-concrete slab like Trapezoidal form Steel Sheet roof in an Industrial type structure ( as you know we use brace elements for stability) ), don't assign Rigid Diaphragm.

Regards

Tnx for your reply. I already modeled it like you said, but the problem is when i model the slab as membrane. I still have moments in the slab...

Can this be correct? I think it shouldn't be.

[san333]

Dear All,

How you modelled the transfer structure in ETABS, especially if you have transfer beam with shear wall above the beam and column below the wall. Is it we need to model the transfer beam as a spandrel or only line/frame element ? My friend suggest me to use the rigid link in between, but I'm not so sure also. Could you share some paper or info regarding this matter. Really need your help.
Thank you very much

---

Edit: What I mean is shear wall above the transfer beam and column below the transfer beam

[cx_oem]

(3) Stiffnes modifiers for beams,columns,walls,slabs needed on when nonlinear
analysis not performed.
core: modifiers should be provided, special for crack condition. UBC and other codes specifics this. There are no full 100% I value in reality.

Usually for beams of moment resisting frame, can be 0.3I (I is for regtangular section), but considering T beam in reality as twice as regtangular beam's stiffness, shoud be 0.3x2=0.7I

[fashion]

Hi Yasir, go to File menu after analysis is complete, click on Last Analysis Log, and check the text file for GLOBAL FORCE... The errors are in percentage.

juice how low should be this percentage so as to be safe e.g. 0%?
thanks

[gacella]

Dear DamirDz,

Always apply Rigid Diaphragm for each story level whether your slab is modeled as Membrane or Shell. But, if your slab is a thin element which would not act as an diaphragm action (for example non-concrete slab like Trapezoidal form Steel Sheet roof in an Industrial type structure ( as you know we use brace elements for stability) ), don't assign Rigid Diaphragm.

Regards

Tnx for your reply. I already modeled it like you said, but the problem is when i model the slab as membrane. I still have moments in the slab...

Can this be correct? I think it shouldn't be.

iN eTABS YOU CAN SPECIFY THE RIGIDITY OF THE DIAPHRAGM BY CHOOSING THE rIGID OR sEMIRIGID OPTION. tHESE OPTIONS AFFECT ONLY THE ANALICYSIS OF THE MODEL. iF THE RIGID OPTION IS SELECTED, A FULLY RIGID DIAPHRAGM I ASSUMED. iF THE SEMIRIGID OPTION IS SELECTED, THE IN-PLANE RIGIDITY OF THE DIAPHRAMG COMES FROM THE STIFFNESS OF THE OBJECTS THAT ARE PART OF THE DIAPHRAGM. IMPORTANT: DIAPHRAMG CAN BE HORIZONTAL ONLY , APLICABLE ONLY TO FLOOR TYPE AREA OBJECTS.