Semi Rigid Diaphragm Properties for Wood Sheathed Diaphragms

[Struct2468]

Anyone have recommendations for diaphragm properties for wood sheathed semi rigid diaphragms? I am doing the analysis in Risa 3D. The material properties are: Modulus of elasticity (Risa used 1800 psf as default), G, and Nu.

I realize the NDS gives a formula for calculating diaphragm deflection. I have a three sided diaphragm so was hoping to capture the actual diaphragm stiffness.

 

[driftLimiter]

I am curious to see what others do for this is well. The semi rigid approach can help significantly with modeling and I'd like to start using it more.

In the past I have created a sample model where I created a simple diaphragm, loaded it up, then calibrate the plate material and section properties so that the deflection matches the NDS equations. The thought being that for similar magnitude of loads and aspect ratios its rational to use these 'calibrated' properties.

Last time I tried it I was struggling with the chord deflection component, I believe I tried modeling the chords but ended up giving up on that.

Next time I do it, I think I will do kind of a sensitivity analysis on the different components in the NDS equation. Perhaps for the purposes of lateral load distribution, some of the terms are less impactful. It would be nice to be able to just use the plate elements without having to model chords and still get a good result from the 3d finite element analysis.

I think there is probably a valid approach just modeling the inplane shear stiffness G' or Geff as it relates to the material thickness and elastic modulus as well but I haven't given much rigor to checking this out.

 

[ChorasDen]

I realize the NDS gives a formula for calculating diaphragm deflection. I have a three sided diaphragm so was hoping to capture the actual diaphragm stiffness.

Wood diaphragm deflection consists of 4 parts as outlined in SDPWS C4.2.2: chord deformation, panel deformation, nail slip, and chord splice slip. All are important to identifying the stiffness of the diaphragm itself, and all are outlined within SDPWS.

I have a three sided diaphragm so was hoping to capture the actual diaphragm stiffness.

Should be the same basic concept, diaphragm stiffness is calculated using the deflection equations, and distribution of load is based on shear wall elements below. I've written a fair amount of my own software for calculating performance of rigid/semi-rigid 3-sided and cantilever wood diaphragm in regards to strength and deflection, is there something particular about the deflection equations that are confusing you?