ASCE 7-05 Section 12.2.5.5

[slickdeals]

Folks,
Please see attached sketch.

I have a clerestory popup roof to which my concrete shear walls do not continue. I have a dicontinuous vertical system.

I need to use SMF because of my seismic design category. However, does Section 12.2.5.5 require me to continue it to the foundation even if I can adequately transfer the shear forces via the diaphragm to the concrete shear walls? This would be very costly to carry my moment frames all the way down just because they support a light roof.

Are there any ways to use the diaphragm to transfer the shear to the walls and carry it to the foundation without violating the code?

Thanks

 

[KBVT]

I agree that I do not think the intent of the code is to require a clerestory lateral system to be continued to the foundation. You would have to increase the lateral forces for the increase according to the out-of-plane offset horizontal irregularity requirements of Table 12.3-1. Are you required to do special moment frames due to building height in SDC D-F??

 

[slickdeals]

Yes, I am required to do it because of the SDC which happens to be "D" and because of the height > 35'.

Any clarification regarding code interpretation is much appreciated.

 

[KBVT]

I've honestly never run into this particular scenario but you could argue that the clerestory is a single-story moment frame system which, as long as your building height is less than 65', would allow you to utilize ordinary or intermediate moment frames. This would preclude the special moment frame requirement and would allow you to waive the continuous to the foundation requirement of 12.2.5.5. I'm not sure if that is truly accurate, just a thought.

 

[ARLORD]

I'm no expert on high seismic design. But, I think it all depends on whether a SMF is required or not. 12.2.5.5 clearly states that if it is required then it must be continuous to the foundation. If not you must meet 12.3.3.2 & 12.3.3.4. However, I don't think section 12.2.5.5 addresses the fact that it SMF is offset from the shear walls at the lower levels.

Again I am no expert on irregularities, but I think you have both vertical and horizontal irregularities.

 

[slickdeals]

I am using a higher method of analysis RSA, in addition to designing them for higher forces as required.

I am just questioning the requirement for carrying a SMF all the way down to the foundation inlieu of transferring them to a shear wall.

I live in Miami and I don't do seismic design on a daily basis, and hence my question to the people who do this day in and day out.

Thanks