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Re: Cantilever System (Help!)

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Title: Cantilever System (Help!)
    Provided you are adequately tied to the roof diaphragm to transfer the required force to the lower roof system, the requirement for a moment connection at the base is absurd. 
 
I have done similar systems in the past.    If the load path is clear and the statics work, the deflections are controlled and all details are well defined, I would explain how the system works and refuse to change it.
 
Paul Feather
----- Original Message -----
Sent: Tuesday, November 07, 2000 10:28 AM
Subject: Cantilever System (Help!)

I have 2- one story wood buildings to be used as senior citizen center. One is 80ft x 100 ft and the other is 90 ft x 90 ft approximately.  Their roof are almost at the same level (17.5 ft.).  In between these two buildings (30 ft apart) are lounge, lobby, and reception area  and it was covered by a higher roof (at elevation 27 ft.).  There is no shear resistance from the lower diaphragm to the higher diaphragm because it is almost all windows. We decided to use steel columns to cantilever out above the lower diaphragm to resist seismic force. The columns are supported at the lower roof level and at the foundation.  I used R=2.2 to get the seismic load at the higher roof.

The plan checker said that this is not an acceptable system because there is no moment base.  He wants the column to be supported at the base only to be acceptable.  My argument is that the support at the diaphragm level and at the foundation level created a couple moment to serve as a moment base.

I just need anyone, especially those that are very familiar with the intent of the code could help me.  I am in a situation that if mine is not acceptable that I have spent more hours to finish the project.  But I need to know which way to go to save some time. 

Thanks in advance,


Alfonso S. Quilala Jr. , P.E.