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Young engineers often ask about whether to select membrane or thin shell or thick shell for modelling area elements such as RCC slab. I am going to talk about the difference in the results when choosing thin-shell or membrane. This is what makers of ETABS says about the topic. I will quote the following to clear out the structural difference between the two: "Load which is applied to membrane objects transfers directly to supporting structural objects, whereas meshed shell objects have bending stiffness and therefore resist a portion of the load through flexural deformation. As a result, less load will be available to transfer to beams located under a shell, while 100% of the load will transfer through a membrane". Lets see how much can the results differ. Figure below shows the partial framing plan of a level in the building I will discuss how the modelling of S11a as thin-shell or membrane will effect the design shear and moment on the beam B54a, see figure above. The figure below shows the design forces obtained against the gravity loads for the membrane case: The figure below shows the design forces obtained against the gravity loads for the thin-shell case: Based on the results presented above, B54a's design shear increased by 155%, and its design moment by 147% as compared to S11a's behavior as membrane. Now the question, that a Structural engineer needs to ask is: Which result is more appropriate or which result captures the actual behavior more realistically? And that is where you engineering judgement comes into play.

Assalamualaikum Everyone, Say i have modelled deck in etabs, and it behaves as membrane. do i need to any modifier to its properties ???? Like if its membrane, probably i am not going to apply m11,m22,m12 modifiers, but what about in plane modifiers like f11,f12,f22, as there is concrete topping, do these need to be modified ?

When a slab is designed in ETABS or SAP2000, usually the Membrane and diaphragm value is assigned to it. One of our structure designing professor assigned values of both membrane and diaphragm same and told us that, this will be always constant and same. I am a bit confused why so? What actually these parameters represents? I only knows the basic definition of Line element and surface element. When i opened the ABAQUS User manual it was clearly defined that, shell thin consider only in plane stresses while shell thick consider out of plan stress also which are i think shear deformations.

Hey Can sm body help me to understand what this membrane drilling rotational stiffness, perpendicular to plane is about ?

When i use Membrane for slab my Manual calculations matches with ETABS and when use Shell thin ETABS gives very small Moment As compared to manual, Can someone explain why,?

Respected engineers! in Etabs while defining slab it asks to select shell, plate and membrane. what is the diffrence between them and when and in which type of slabs we will use these?

Aslamualikum: I want to ask that, in ETABs, when we define slab, I put slab thickness same in MEMBRANE & BENDING, is it right or wrong? and what is difference b/w shell,membrane,plate and thick plate? and how and when we use these ? read out help topic in ETABs. But i could not understand.. Can anybody explain me in bit simplest way.?