Flexible roof diaphragm shear wall load distribution question?

[RobertEIT]

Please see attached diagram, we know that for flexible diaphragm, if two shear walls are not in a same line with shear force as in Fig.1, the shear load is distributed to these two shear walls by their tributary area. But what about the two shear walls are in a same line in the shear force direction as shown in Fig. 2?

My oppinion is in Fig. 2 case, the shear load will still distributed to the two shear wall based on their relative rigidity, not based on their tributary area. i.e. shear wall A will take twice as much shear load as shear wall B. Am I right?

Thanks a lot for you guys precious oppinion.

 

[Lion06]

Yes, that seems correct. The shear you show as V, would be the reaction at that end, based on trib width, not the applied story shear. That being said, the idea is right.

 

[JAE]

You are correct.

Don't confuse the load path through the diaphragm with the load path along the collector.

The flexible diaphragm will, theoretically, distribute load through itself in simple-span behavior, regardless of the flexibilities of the supporting end braces.

Once it hits the end braces, the diaphragm is no longer part of the load path...the load is now "in" the collector and the collector releases load based on the relative stiffnesses of all that connects it to the ground.

Thus, the longer shearwall would take more load than the shorter shearwall.

 

[haynewp]

The shear walls in figure 2 take shear based on their lengths, not rigidities for a flexible diaphragm. You can see examples in Breyer for collector diagrams that illustrate this.

 

[JAE]

haynewp - isn't "length" in shearwalls equivalent to "rigidity"?

Generally it is thought so.

 

[kslee1000]

Agree with JAE.

 

[haynewp]

Generally yes, if you are including bending or mixing materials then no. I was just trying to be technically correct.

 

[JAE]

gotcha

 

[msquared48]

I thought that the term was politically correct...

Mike McCann
MMC Engineering

 

[vandede427]

I wouldn't use the term "relative rigidity" for flexible diaprams and wood shear walls. seems like these terms are reserved for rigid diaphrams.

with two or more shear walls in-line with eachother, the amount of shear each wall takes is based how much linear load the collector dumps into it.