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RISA Wood Wall Panel and Point Loads

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phamENG

phamENG

Structural
Feb 6, 2015
7,669
So I'm about to make the jump back to RISA. It's about 6 months earlier than I'd planned as I'm still halfway through my last software annual payment, but I keep getting frustrated by its shortcomings and lack of features. Now I have a project that needs software (I don't have a month to do all the calcs by hand), but mine can't do it because the members are not prismatic. Womp womp.

Before I do, I'm curious about one thing that I can't find explained anywhere.

If I design a floor system with a girder that puts a point load in the middle of a wood wall panel, does RISA take it into account for stud and header calculations? Header is certainly important, but for the studs does it try to spread it out like it's a concrete wall or does it define a discreet multi-ply post or a column in the wall for the point load? I don't need a 3D analysis program to design a simple box...it's the odd ball creative stuff that the architects come up with that leave you scratching your head about load paths for days that this is useful for. And I don't want to start and stop a wall on either side of a post if it's meant to be a continuous shear wall.

It's been a few years since I used RISA. Version 16 I think was the last time. I might have downloaded 17, never touched the new interface.

Thanks.
 
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I believe wall panels in RISA use the average FEM force in each defined region of the wall. Regions are automatically created at openings, but otherwise the wall is designed as a single region. So I don't think the software is capable of designing a discrete post or built up member directly below a concentrated load. I usually just explicitly model a post where I know I will need one.
 
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If I design a floor system with a girder that puts a point load in the middle of a wood wall panel, does RISA take it into account for stud and header calculations?
Click to expand...

We're talking about RISA-3D, right?

Check with their tech support group to confirm. But, I don't believe RISA-3D will do this. In RISA, wood wall panels are analyzed / designed primarily for lateral forces. At least that's the way it was when I worked there.

Here's the problem, the "gravity" loading of a wood wall is supposed to be handled by studs and headers. But, I don't think RISA-3D knows about those at all. RISA-3D is looking at the wall primarily as a series of plate / shell elements. These elements stiffness (both shear and axial) are adjusted to "mimic" vertical stiffness from studs and lateral stiffness from the plywood or OSB sheathing. But, once one of those plate elements is loaded, it disappears into the the FEM analysis.

RISAFloor is a little bit "smarter" for gravity loads because that's all it does.... manage loads for gravity and distributed that load to beams, columns and walls to carry down to the next floor below.
 
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Thanks, guys. That's what I was afraid of.

Josh - yes, though if building the floor in Floor and linking to 3D made it happen, that's fine. I'll probably sign on for the whole package anyway.

I'd switched to SAFI GSE about 5 months ago - it's great for wood. It does shell elements to work out lateral, but then it "builds" the wall with studs and analyzes them as discreet members for axial and bending loads. If you have a point load it will create a post under it. It's really neat. If RISA could do something like that, it really would be the best multi-material 3D analysis package.

Sadly it doesn't do a lot of other things...like Masonry, or steel connection exports, or tapered steel members, etc. And I'm starting to feel the pinch of those shortcomings since those are the things that software really saves time on.
 
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I believe that point loads tend to get smeared over the wall, i.e. no dedicated stud pack below the point loads. I know it sucks to trace those loads by hand down, but that's often what I end up needing to do. Use the risa results for global analysis but for discreet things like a point load on a wall I still do the old fashioned way. The nice part is I can just pull the beam reactions right out of the model.

How far down you need to check things by hand is really a function of what's happening down below.
 
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It probably wouldn't be too difficult to program a feature that can create a skinny wall region directly below a girder. Then the force results for that region could be used to size a built-up stud or post member. Not sure if that could be done as a manual workaround with the current version.

It would be worthwhile to send a feature request to RISA.
 
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