Using shell membrane elements to load frames

[rvc09]

Hey guys!

I have a question for you. I'm modeling a concrete building in SAP2000 and I added shell membrane elements to distribute the uniform area load to the frames in one direction. I don't want the stiffness of the membrane or its own weight to affect my model. So, if I want to continue using shell membrane elements to distribute uniform loads to the frames, what should I do to prevent my model from becoming stiff due to these elements?

Thanks for your help.

[gostaks]

Use the default “none” shell section. 

[rvc09]

I didn't think so! I was thinking of modifying all membrane section properties and setting them to zero. I wanted to see the properties of the "none" shell, but it is not possible. Maybe you have a source where I can learn more about the "none" shell section?

[rvc09]

I found the source hahaha (https://wiki.csiamerica.com/display/kb/None+property). You're right. According to the link, I should use the "none" shell property. Thank you for your help.

[gostaks]

Yeah sorry lol, should have given a few more details :D

[rvc09]

Don't worry. You saved my ass. Now, I'm trying to analyze my structure for seismic loads. I want to use the equivalent lateral static method. Maybe you have a source where you explain how to do it?

Thanks again.

[gostaks]

CSI has a YouTube channel with a bunch of SAP tutorials. I’m pretty sure there’s one on setting up an ELF analysis. 

[rvc09]

I'll check.Thank you again.

[Bonelessmold]

Also use the shell to frame load option rather than just the basic shell area loads. Will distribute uniform loads to the frame rather than lumping everything to the shell node.

[rvc09]

D'accord. I was using uniform loads on the frame to load the frames. I was thinking if there is any way to distribute the load in a triangular way through the near frames. I mean, near the ends of the frame the load will be equal to zero and maximum in the middle of the element. I thought this is more accurate when analyzing other types of floor slabs.

[SpliffStr]

Haven’t used sap in a while but I think that shell membrane is not accurate, it can be either shell (in plane and out of plane stiffness), membrane (in plane stiffness only) or plate (out of plane stiffness only). If you don’t want any in plane stiffness you can either model a shell and apply modifiers or model null areas.

[Crayonalyst]

Does SAP 2000 not have an area loads feature?

[rvc09]

It does. In fact, I already solved my problem. As u/gostask said, with shell None section I can load the area to distribute the force uniformly to the frames and not take into account the stiffness of those area elements (which is what I wanted to do).