Linear Release on Edge of Slab - Etabs or Robot

[zstone]

Hi Everybody

Im new in Etabs,
I'd like to define a linear release on edge of slab, for example: conection of slab with wall to be pinned, not fixed,
With Robot Millennium this is posible and very easy,
is this posible in Etabs or SAP

regards

 

[stressed]

Why not define the wall using membrane type area? That's easy enough, and it gives you the pinned connection at the slabs.

 

[zstone]

thanks stressed for help
you idea is correct
i dont know what will hapen with bending moments in slab,(moment values in case of pinned edge - and moment values in case of wall modeled as membrane - dhe values o bending moments in slab must be same in to cases of modeling)
i will try it

 

[jugurtha12]

I do it with sap and i think that is very easy with sap we select the area element then we right clik then we dot it with joint offset overwrite
sory for my english

 

[drile007]

Why not define the wall using membrane type area?

OK, but when try to do a dynamic (response spectra) analyisis walls defines as membrane type will vibrate perpendicular to their own plane! First dozen mode shapes will be just described shapes and we don't want that! Can we prevent this effect?

 

[stressed]

Since it now appears both zstone AND drile007 are experiencing a near identical predicament, I'll offer my $0.02. As with any problems you experience with a structural software package, if you're getting strange results, then don't be shy about getting creative and experimenting with some alternatives, for example 1)define or assign property modifiers to a shell type wall bending properties such that it acts like a membrane to give you the desired pin connetion 2) mesh the wall and assign only a small bottom sliver of the wall connecting to the slab to be membrane with the rest of the wall assigned as shell type 3) if #1 and #2 don't result in suitable results for both static and dynamic analysis, then create one model for static analysis and another model for dynamic analysis 4) If #'s 1, 2, or 3 don't work, then drink a bottle of Jack Daniels, put the gun barrel in your mouth and, oh wait....just teasing

zstone/drile007, let us know what you find. I'd be curious to learn for myself from your experience. Good luck.

 

[drile007]

1)define or assign property modifiers to a shell type wall bending properties such that it acts like a membrane to give you the desired pin connetion

I already tryed this and I got the same results as I described in my previous post.

2) mesh the wall and assign only a small bottom sliver of the wall connecting to the slab to be membrane with the rest of the wall assigned as shell type

I think that this kind of assignements doesn't describe real behaviour of the wall state.

 

[civilhak]

Hi people,
should this not work if you define walls as shell elements and plates as membrane elements????

 

[stressed]

drile, by releasing moments at the wall/slab intersection, the physics of the problem would seem to dictate a (possibly significant) change in the dynamic modal results, whether or not you model with frame elements or shell/membrane elements. Could you explain what results specifically that you are concerned with that is causing you problems?

 

[drile007]

What happened if you define walls as membrane type:
Such (membrane) elements don’t have any stiffness perpendicular to their own plane, or with the other words; they can't "possess" any moments because their inertia moment is zero. Furthermore, they can't "resist" to any force perpendicular to their own plane.
And what happened in dynamic analysis? When we mesh the wall we automatically add mass at each wall node. When we add horizontal accelerations (response spectra) we got horizontal forces perpendicular to walls in each node (mass x acceleration = force). Since wall is very soft to forces perpendicular to their own plane, we got huge displacement (mode shapes) perpendicular to their own plane.
I hope that I didn't miss the point and I use the right words since my mother language isn't English.
To avoid this problem I do what civilhak suggest, I define walls as shell elements and plates as membrane elements!

 

[BrankoK]

ZStone: Why don't you ask CSI? It usually takes them up to 1/2 hr ro reply.

Cheers,