×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Self-generated Response spectra

Self-generated Response spectra

Self-generated Response spectra

(OP)
I am working on a model of an elevated water tank in RISA3D 2018 and I am generating my own response spectra to use with the model. However, when I try to do a response spectra analysis with this, I get an error saying a diaphragm link of zero length has been detected and that I should do a model merge and try again. When I do this, the program crashes when trying to solve again. The analysis runs fine when I use the built in response spectra such as ASCE 2016, parametric design spectra, but only when I use the self-generated spectra does it crash like this. Any ideas on why this is/how to fix it?

RE: Self-generated Response spectra

I've got a couple of suggestions.

1) After you do the model merge, you want to select the entire model, then go to the delete tool. That tool has a checkbox that says something like "delete selected zero length members", right? If so, make sure this is the only box checked and then proceed to delete.

RISA doesn't have a true rigid diaphragm feature and they instead use internal "rigid links" to create the diaphragm. That's fine, but they also make sure to place one wherever you have a member so that they can be sure the member doesn't accidentally receive any axial load.... That used to happen sometimes because of the fact that they don't use a true rigid diaphragm constraint.

If you get a zero length rigid link, bad things will happen. That error message about model merging might need to be updated to reflect the fact that these any zero length members could be the problem. Actually, just as likely is that you had a NEARLY zero length member that became a zero length member after the model merge.

2) Do you have anything that requires internal meshing (wall panels). Or, maybe you have a partially rigid diaphragm that is coming over from RISAFloor? If so, the meshing algorithm from these elements could be causing an issue. If so, that's tough to find on your own. You might have to just send it off to tech support.... or post the model here and I can take a look. Though I am pretty busy with my day job (working for a RISA competitor!) at the moment. Plus I don't have access to a full RISA license anymore and usually use the Demo version when I try to help people understand / fix their models.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close