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Re: Braced Frame Question

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Chris Palmateer Wrote:

>I'm curious how others are designing the connections for their chevron 
>braced frames.  Specifically, with regard to UBC Section 2211.8.3.1, I would 
>be curious at how other engineers interpret item 3.  I have always designed 
>these connections for item 2 and another engineer in our office is trying to 
>convince me that this is too conservative.  His position is that per 
>2211.8.4.1 the brace itself is only designed for 1.5 times the *seismic* 
>forces (gravity loads not included), so this is the maximum force that can 
>be transferred to the system.  Well, how does everyone else read/interpret 
>the code?
*****************************************************************************
I have always interpreted item #3 as letting the weakest member go to yield (maximum force).  Assume that your brace is the weakest member per your co-worker.   If you design your brace using the provisions of 2211.4.1 increasing the design load by 1.5 and consider that generally under ASD, the stress is limited to 0.6 Fy (Safety Factor = 1.66), then the "real" capacity of your brace is about 2.5 times your design load (approximately 3*w/8 time your prescribed seismic loads).  My interpretation has been that if you go to all the trouble to ensure your braces do not fail, then don't let your connections cop out early.

Bruce Hopper
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