Lower Roof Diaphragm - Chord Loads Mid-Floor Diaphragm Ht

[cuels]

I have a 3-story hotel that has a lower lobby and pool roof that intersect the main building between the 2nd and 3rd floor diaphragms. In addition, my shear wall lines do not line up with the main building. Can I treat the lower lobby and pool roof as a separate building with its own shear walls, or do I need to add a floor to floor beam that transfers drag strut forces to the 2nd and 3rd floor diaphragm? Nothing lines up, so I am not quite sure how to treat these lower roof diaphragm loads. I have the shear walls to resist them, but what do I need to consider where it is part of the existing building? It would sure make it clean to just consider that the lower roof diaphragms are isolated from the main building and handle their own shear there.

Included is a print of the plan I am dealing with, if it helps. The main building shear wall lines are E, F, and G. The Lower Roof diaphragms are lines E.1 and G.1. The lower roof diaphragm top plates will be at 16' high. The 2nd and 3rd floors are at 10' and 20' high.

 

[msquared48]

If the first floor is a concrete podium, then you could most likely treat the first floor level as a seismic base, separate from the basement level.

If the first floor diaphragm is wood though, you have to transfer out the shear walls above to the shear walls below as one building.

Mike McCann
MMC Engineering

 

[cuels]

How does that relate to the braced wall lines not being aligned and the diaphragms at different levels? I think that answer may have been an answer to my previous post about transferring shear through a basement level.

In this case there is no basement below. I have the problem with shear walls of the lobby and pool areas (lower roof elevation) intersecting the main building diaphragm between floors and not aligned with my main building shear walls due to the lobby and pool roof diaphragms.

 

[RFreund]

It looks like the West shear wall of the pool area terminates at the 2nd floor. Is that correct? Or is that section just cut at an opening? What portion is existing?

The shear walls in Room 216 and 218 - these terminate at the second floor. How are these forces transferred to the fist floor? If the only shear walls on the first floor are the pool and lobby walls then the force applied at the second floor by shear walls in room 216 and 218 need a load path to get to the shear walls that go down the first floor / foundation.


EIT

http://www.HowToEngineer.com