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Re: Cantilever System (Help!)

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Hi Alfonso,
    From what I gathered, you used those steel members as cantilevered
beams in a vertical postion to take lateral load out of the high roof
into the lower roofs of the two low buildings. As long as you can
demonstrate force path clearly and design connections properly to the
lower roofs, plus that the loads can be absorbed by the two low
buildings, I cannot see why your approach not work.
    Did the plan checker mistake the high roof treated as an independent
structure. With
limited info, it is hard to judge here.
    Probably you might need to explain your approach personally again
with the checker rather than submitting another design.
Regards,
Chris Tse
Sunnyvale, CA

Alfonso S Quilala wrote:

>
>
> 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.

Alfonso S Quilala wrote:

>
>
> 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.