huangyhg

modeling a chevron brace
i am attempting to model a chevron brace in visual analysis, but the program is giving me an error message stating "the model has fewer than 25 degrees of freedom (dof), modal analysis cannot be performed. you can split members or plates to get enough dof for a modal analysis."
brace information: the length and height of the brace is 33 feet and 18 feet respectively. the columns and braces are 6x6x3/8 tubes. the beam is w14x43. my model has pinned bases and the moments are released at the ends of the beam at the column locations, and at the end of the braces or diagonal members.
i would greatly appreciate any help in modeling the brace and directing me to a source. this is my first chevron brace design. it is being used in a low-rise industrial building.
sincerely,
paul (pat2)
pat2,
i'm not familiar with that particular program, but it sounds like too many joint releases. first thing that comes to mind is did you release the torsional restraint of the braces or beam? if so, just fix the torsional restraint. if torsional release isn't the issue, could be too many pins at one joint. at least one
first of all are you doing modal analysis or a static analysis?
shepherd and 3dboy,
thank you for responding.
i am attempting to run a modal analysis.
pat2
have you contacted ies yet? they are typically very responsive to people.
jeremiah
well does the bracing
i'm not familiar with that particular program, but the program message seems to indicate that you need more nodes in your model as it (the program) cannot develop the desired number or quality of mode shapes.
you could add intermittent nodes along the beam and columns to provide additional dof for the modal analysis.
that said, i'm not sure why you are doing a modal analysis of a single brace model. modal analysis should normally be performed on the entire structure together, not on a single brace component.
it ended up being a program limitation. i needed to break the members up to create enough degrees of freedom for the program to work.
thank all for their help.
paul

__________________
借用达朗贝尔的名言：前进吧，你会得到信心!
[url="http://www.dimcax.com"]几何尺寸与公差标准[/url]