Modeling floor bracings in RISA 3D
Modeling floor bracings in RISA 3D
(OP)
Hi !
Some of you guys, knows how to avoid that the floor bracing
take loads from the area load in RISA 3D.
Obviously bracings don´t work in bending, but my results in RISA 3D, shows bending moments due to the area load I´m applied to my floor. What can I do in order to avoid this problem ?
Thanks
jatfuentes
Some of you guys, knows how to avoid that the floor bracing
take loads from the area load in RISA 3D.
Obviously bracings don´t work in bending, but my results in RISA 3D, shows bending moments due to the area load I´m applied to my floor. What can I do in order to avoid this problem ?
Thanks
jatfuentes





RE: Modeling floor bracings in RISA 3D
Also, don't forget that your modeling doesn't dictate the reaction of a structure....the structure will react based on its loading and connections.
JAE??? You're the RISA Guy....
RE: Modeling floor bracings in RISA 3D
I'd think you might be able to try a few options:
1. Model the diagonal braces with their proper area, A, but model them with a very very small Ix such that they simply may not take as much load. I'm not sure this will work because I think the area load is apportioned to members, not based on relative stiffness, but simply on their tributary area.
2. Model the braces at a slight (0.25") lower elevation. This will require double nodes at the ends of the braces and some sort of fictitious rigid member to tie the braces and the floor framing together. This may allow the load to "skip" the lower braces and proceed as you want.
3. Don't use the area load generator - simply apply distributed loads on each member manually. This takes a little extra time - but not that much - RISA is very fast to use and input data.
4. Finally, call RISA direct - or email them. I've found that they are very helpful. www.risatech.com
Ron calls, I answer
RE: Modeling floor bracings in RISA 3D
JAE, I think the third option is more easier.
I will apply the load directly on the beams in the places where I have diagonal floor bracings.
RISA could improve this problem that come´s since version 4.5. Ex " IF the element is a bracing floor,
THEN Ignore. "
Thanks again .
Jfuentes
RE: Modeling floor bracings in RISA 3D
I'm going to upgrade my structural software this summer and have narrowed it to RISA 3D, STAAD-Pro, and GT-STRUDL, with RISA holding the lead at the moment.
RE: Modeling floor bracings in RISA 3D
I don't know much about GT-Strudl and Staad as far as today's versions go - just a little long-ago experience that perhaps jaded me against Staad.
RE: Modeling floor bracings in RISA 3D
Have played with the RISA 3D demo and it looks like a pretty good program. Easy input and plenty of options for output, though it currently doesn't do aluminum code check and that's about 80 percent of my structural analysis. That's OK though, 'cause I'm not much on code checks by software anyway. Still prefer to do a fair amount of manual post-processing...shows my age!
Sorry Jatfuentes....didn't mean to hi-jack your thread!
RE: Modeling floor bracings in RISA 3D
RE: Modeling floor bracings in RISA 3D
RE: Modeling floor bracings in RISA 3D
I'm not an experienced spreadsheet user, but isn't it fairly difficult to program a spreadsheet to do code checking when there are many load cases. Just curious, I too have been reluctant to do much work with built in code checking, and instead continue to use my own calculation program.
Regards,
-Mike
RE: Modeling floor bracings in RISA 3D
I've written many spreadsheets that cover multiple load combinations. For some RISA models I've made, to strictly satisfy the code, there can be a LOT of combos to check -
Plus or minus Wind in one direction, in the other orthogonal direction, with roof live, without, with crane loads, without, plus/minus seismic, plus/minus seismic with overstrength factors, etc. Its amazing how many get generated. But a spreadsheet can be set up with multiple columns to check all of them if needed.
I also wrote a nice big spreadsheet that allows me to model a concrete frame in RISA and copy/paste in a moment envelope of axial, shear, and moments along the span of beams or joists and then determine all the reinforcing for that span. Concrete makes multiple load combinations easier as you can design for an envelope rather than having to check each and every combination like in steel.
RE: Modeling floor bracings in RISA 3D
Over the years I've written many programs in BASIC, then QuickBASIC, and now VisualBASIC, the result being that I never learned spreadsheets. Recently I have become interested in Mathematica and while extremely powerful it is sometimes awkward in my opinion for engineering type programming. I occasionally wonder if I should have done some of this in a spreadsheet.
I agree about how easy it is to end up with many load combinations. I just design elevated bins now, but analyze these structures for either 22 or 26 load combos depending on whether orthogonal seismic is required. If you put two bins on a common structure and consider that one may be full while the other is empty, or both may be full, will at least double the load combos. Because of load combos even simple structures can be difficult to do by hand.
Regards,
-Mike