Flexible diaphragm of industrial building and accidental torsion

[LuisUgarte]

Hello everyone,

I've tried to find a good reference to understand, if it is nedeed to consider accidental torsional moment in the seismic design of an industrial building, with flexible diaphragm.

Regardidng industrial buildings we do not consider any rigid diaphragm, instead we use roof elements (tension rods and struts) to provide a good load path for lateral loads. In that case, it is required to consider accidental torsion? If so, how will you distribute that accidental torsional moment between bay frames?

Thank you!

Regards

 

[driftLimiter]

Horizontal bracing schemes are generally treated as flexible diaphragm.
ASCE7 suggests that for flexible diaphragms accidental torsion is not required to be applied. See sections 12.8.4.1 and 12.8.4.3 of 7-16.

The 'penalty' is that we need to design the diaphragm for the masses where they lie.

For example if you have a CMU shaft in a light frame building, there is a concentration of seismic forces due to the CMU. That means whatever flexible diaphragm region that sees that load has to carry the entire effect.

Conversely on a rigid diaphragm building, All of the elements in the lateral system would resist the concentrated forces, but the center of mass will shift, and induce a torsional moment.

 

[HTURKAK]

Pls look Section 12.3.1.1 if your conditions match with the conditions under which the diaphragm can be classified as flexible without calculation. I would like to remind that if the lateral system composed of vertical steel braced frames the diaphragm may be considered as flexible. The same diaphragm should not be classified as flexible for the lateral system steel moment frame.

I would suggest you to perform analytic procedure (12.3.1.3 Calculated Flexible Diaphragm Condition. ) to see if the diagram is flexible.



He is like a man building a house, who dug deep and laid the foundation on the rock. And when the flood arose, the stream beat vehemently against that house, and could not shake it, for it was founded on the rock..

Luke 6:48

 

[driftLimiter]

Horizontal bracing schemes are generally treated as flexible diaphragm.

To HTURKAK's point, this can be calculated according to procedure. I concede that simply 'treating' it as a flexible diaphragm can be insufficient.

 

[SE2607]

I concede that simply 'treating' it as a flexible diaphragm can be insufficient.

...because a dog only has four legs.

 

[LuisUgarte]

Thank's everyone for your valuable help. I'm aware that the flexible diaphragm condition must be checked first and be designed accordingly. My doubt was about the accidental torsion for industrial buildings. How do you approach it.

Regards

 

[lexpatrie]

Flexible diaphragm won't develop accidental torsion.