Hi, I plan to attach a sheet to a steel frame using riveted connections to brace the steel frame. The sheet will be fastened with rivets along the entire edge area. To simulate this sheet, I modeled surfaces as membranes with the sheet thickness. However, in the design, I get serviceability| deflection in the z-direction. But the sheet is only supposed to brace, just like an X-bracing. Is the deflection in the z-direction even important then? And is there a way to model the sheets as X-bracing?
Hello Tk259,
it is hard for me to understand you model. Is it possible to provide the model so that I can reconstruct it better?
Thank you in advance.
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Hi Thomas,
As part of my bachelor's thesis, I am building a somewhat more complex tower. I want to stiffen some walls in this tower with sheet metal. As mentioned above, I am reluctant to model the stiffening sheet metal as a membrane surface because then I get the aforementioned error in the design. One model shows my approach with X-bracings as a sheet metal substitute. There, I used a cross-section value for the bracings that I took from a structural report, where sheets were also represented as X-bracing. However, the results for the approach with the sheet metal are very different. The model with the sheets is already somewhat further developed, so please don't be confused by that. It is purely about the approach of whether and how I could model the sheets as X-bracing so that the stiffening effect is well represented. In reality, the sheet is also only supposed to transfer tensile forces and not contribute to stability in any other way.
Turm_mit_BracingalsBlechersatz.rf6 (1.9 MB)
Turm_mit_Blech.rf6 (1.8 MB)
I came across your post purely by chance and became curious,
I probably am not providing you directly with the solution to your problem here, but at least these could be some approaches and ideas that might lead you in the direction of your purely tension-loaded surfaces.
First of all, it would obviously help you to get rid of the bending and shear forces vx, vx. For this, you could switch to a different thickness type:
I think that the wall-shear-free option would already bring you much of the desired effect:
For this, you would have to set the stiffness type from membrane to standard, but I think that is not a big deal. Essentially, the difference would be that with a membrane you have constant stresses through the thickness (layer sides), whereas with “standard” surfaces this would not be the case => but since we would exclude shear and moments through the thickness type, the stress should be constant within all layer thicknesses of an FE node anyway, if I am not mistaken, so that would not make a difference. The problem you would still have, however, is that normal compression forces could of course flow and you want to model the walls as completely “compression slack.” On the one hand, it is of course questionable to what extent this compression slackness is not sufficiently represented anyway, since the stiffness of the 1 mm thick wall should be correspondingly low, i.e., it would take up rather little compression, but to model it that way anyway, you could work with nonlinear line hinges!
Try experimenting with it as shown in the picture; I mean that if you set it correctly, you can achieve that only tensile forces can be transmitted at the corresponding edge. Unfortunately, I had convergence problems in my first attempt but maybe I also did not use it as you imagine, or perhaps I applied the pure tension connection at the wrong place. The other option, which I personally respect more to use because it is easy to set something wrong or, let's say, accidentally manipulate the load flow differently than intended, would be nonlinear line releases. Basically, similar to hinges, hinge conditions can be created between several objects that originally shared FE nodes of a line and can be somewhat separated from each other. It is best to use a clearer file with fewer elements than your complex tower at first. Even if I probably could not fully solve your problem, I hope I was able to provide you at least some support for your high-rise building. 
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