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Re: UBC seismic connection

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BILL PULYER wrote:
> 
>    UBC 97 section 2213.8.3.1 states that bracing connections must be
> designed for the least of three (3) different cases.  One of the cases is
> "The maximum force that can be transferred to the brace by the system".  It
> has been suggested that the only way to obtain this value is thru a static
> push-over analysis or a non-linear time history analysis.
>    Could someone explain (to a person not experienced in high-seismic design
> requirements) the definition of "maximum system force transferred to the
> brace" and how this value is normally obtained?
>    The building is Seismic Zone 3, Soil Profile SD, Importance 1.0, Ca 0.36,
> Cv 0.54, concentrically braced steel frame.
> 
> Thank you in advance for your input.
> William Pulyer P.E.
> 
Look for the provisions (sorry don't have my code in front of me) that
contain statements with Ry.  Generally, the approach is to estimate the
maximum capacity of an element and use that as the design force.  If a
connection breaks, why design the entire brace for what it can't
possibly see?

For example:
Tension brace upper bound might be:

Tn = 1.1*Ry*Ag*Fu (This is member strength, not applied force)

The 1.1 is an indirect "load factor" and Ry accounts for steel strength
variability.  Ag is gross area and Fu is ultimate strength.  Based on
that, you wouldn't have to design any connection for more than Tn. Note
that there is no phi factor in the equation.

Hope this helps, 
Jake Watson, E.I.T.
Salt Lake City, UT