## Wood shear panel modeling in FEA program

## Wood shear panel modeling in FEA program

(OP)

Hi all!

Need some help in wood panel wall model design process. Does anyone tried to make something similar ?

For the beginning i'm started with beam frame design and plywood cladding in 2D modeling environment to

understand is it possible to design something like that at all... and right way faced with problem.

If i want to design panel easy as possible, but in same time precisely and close to reality, i have to figure

out how to design fasteners in most simple and efficient way. In program i can add spring constant between frame beam and plywood

cladding like translational release. Spring constant is measured in Kn/m2. Question is can i use it to simulate

functioning of fasteners and how to calculate it ? Or maybe there is any more simple way to do it ?

Any help will be highly appreciated and sorry for my english.

Thank you!

Need some help in wood panel wall model design process. Does anyone tried to make something similar ?

For the beginning i'm started with beam frame design and plywood cladding in 2D modeling environment to

understand is it possible to design something like that at all... and right way faced with problem.

If i want to design panel easy as possible, but in same time precisely and close to reality, i have to figure

out how to design fasteners in most simple and efficient way. In program i can add spring constant between frame beam and plywood

cladding like translational release. Spring constant is measured in Kn/m2. Question is can i use it to simulate

functioning of fasteners and how to calculate it ? Or maybe there is any more simple way to do it ?

Any help will be highly appreciated and sorry for my english.

Thank you!

## RE: Wood shear panel modeling in FEA program

For design work, I would recommend using a plate FEM model based exclusively on the sheathing. Then you can modify the shear modulus based on the "apparent shear stiffness" (Ga) concept from the NDS special design provisions for wind and seismic (SDPWS). Even that can get relatively complex...

## RE: Wood shear panel modeling in FEA program

## RE: Wood shear panel modeling in FEA program

Beams and columns are straight forward enough but load bearing wood stud walls with plywood (or not) are more troublesome.

What program are you using to model?

## RE: Wood shear panel modeling in FEA program

I have done many many remodels on very old houses, 1940's to 1950's that have been through earthquakes and they are still structurally sound and they don't even have shear walls with plywood. Only exterior stucco walls.

So let me ask you something, if you determine that the end deformation of the shear panel is just a little to much in your model I am assuming that you may increase the shear wall stiffness or utilize a different system, is this correct? Have you considered what this actually means in "reality"? If this is done for the entire lateral force resisting system on a single family residence the house will be too expensive to build.

## RE: Wood shear panel modeling in FEA program

=> HouseBoy I'm working in Dlubal RFEM program.

## RE: Wood shear panel modeling in FEA program

## RE: Wood shear panel modeling in FEA program

1) I totally understand the desire to do this via FEM. If only to validate the many (sometimes dubious) assumptions made during your hand calc.

2) The desire is to replicate traditional design concepts. That means using the studs only for resisting gravity loads, and the sheathing only to resist shear. It also means OTM is resisted exclusively by the chords / hold downs.

3) The problem is that these traditional assumptions don't really match up with a complete FEM analysis of studs, sheathing and nailing like you are trying to do. That coupled with the fact that your model will be incredibly complex.

4) The solution (at least when RISA implemented it) was to use a simpler FEM model. Then use this model to pull out results that could be used for the design of studs, sheathing and such.

5) The model consists primarily of an orthotropic plate element whose shear stiffness was based entirely only the sheathing (adjusted for the nailing by using NDS Ga values). The vertical stiffness and out of plane stiffnesses of the plates were based on the studs.

6) When the FEM analysis was run, you get large shear stress risers around the openings and such. Instead of using the max shear, the average shear stress over the area of each "block" was used for calculating the shear demand in that block.

7) Then to get strap forces, we run the "internal force summation tool" to look at the moments between adjacent blocks. And, use those moments to design the straps.

8) Lastly, the same thing was done at the bottom of the wall to come up with hold down / chord forces.

I'm in the early stages of writing a paper comparing the RISA method for FTAO to traditional hand calculations. But, it's something that's moving very slowing since I'm doing it entirely in my free / after work time.

In my opinion, this method works really well for a single wall. Much better than hand calcs. That's because it is produces a design that always obeys statics and is consistent with it's own assumptions. The hand calc method rely on a number of dubious assumptions about points of inflection and such. Maybe those assumptions are valid for walls with simple and symmetric geometry. But, the more complex the geometry the worse those assumptions become and the harder it is to justify your hand calcs.

Now, if you're putting together a whole building, I'm not so sure that the FEM model is quite as useful / accurate. At least not without some adjustment. The problem is that the FEM stiffness of the individual blocks within a wall is totally reasonable and consistent for determining the forces within the wall alone. However, the assumed stiffness of the overall wall (based on NDS / APA equations) doesn't quite line up with what you get from the FEM model. Therefore, when you have multiple walls or combine wood walls with moment frames or masonry walls or whatever, the relative stiffness of these would walls would have to be adjusted to match the NDS / APA equations. If not, then the force distribution between lateral force resisting elements may not be what you want it to be.

## RE: Wood shear panel modeling in FEA program