Seismic Forces on Diaphragm (Canada) 1

[srazahz]

Hello,

I have a concern regarding diaphragm design for seismic loads in Canada, I am new to this so please pardon the simplicity of my question:

In a multi story building, when I get the seismic story forces, do I use those (Fx) or do I compute the Fpx values for diaphragm design? Also, do I use the individual story forces or cumulative going from top to bottom?

Would really appreciate any help. Thanks.

 

[JAE]

Bump - Anyone help srazahz?

 

[msquared48]

You should usually be dealing with the individual story forces for the floor diaphragm at any particular level, not the sum down to that level.

The shear walls or moment frames tale the story forces from above from the diaphragms above.

Mike McCann, PE, SE (WA, HI)

 

[msquared48]

BAretired or Kootk should weigh in here...

Mike McCann, PE, SE (WA, HI)

 

[srazahz]

You should usually be dealing with the individual story forces for the floor diaphragm at any particular level, not the sum down to that level.

Thanks for the answer, that is my opinion as well.

 

[KootK]

1) I am a Canadian practitioner who does mostly US work for what that's worth.

2) Where are you getting the term [Fpx] from? That means something specific in the US codes but, to my knowledge, is not part of the NBCC procedure (shown below).

3) In general you use the [Fx] values for each floor amplified for capacity design for diaphragm design and not the total story shear at a given level. Do keep in mind that there are situations where diaphragms are called upon to pass significant loads among themselves and loads may be much higher than the [Fx] values as a result. See the NBCC commentary section below for some specific examples of this.

4) Be aware of the alternate procedures available for wood and steel diaphragms in low rise buildings for which inelastic diaphragm behavior is permitted.

 

[srazahz]

Thank you KootK, your answer has been really helpful.