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Re: EBF's

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>EBF requires the link beams to yield first and absorb energy.  It is
>commonly known that Mill Test Reports (MTRs) provided by the
>steel mill generally show that steel has considerably higher
>yield strength than the nominal yield strength (Fy).  I am curious how you design to ensure that yielding will occur at the link beam first?

>Y. Henry H

The link beam is selected based upon the seismic loading.  Thereafter, the other components are selected such that they have a capacity of 1.5 times the strength of the link beam.  By using the same grade steel throughout the EBF, the ratio of actual yield to nominal yield should be relatively close for all the elements.  If the actual yield is higher than the nominal yield for all the steel sections in the system, the link beam is still the weakest element in the system.

Forgive me for doing this, but this is where the thread forks.   Implied in your message is that the lateral system in this building will require more seismic load to reach first yield than it was designed for.  Should we be using a number which better approximates the actual Fy in the design of EBF's rather than the nominal Fy?  Doing so would force the system to respond at force levels consistent with the design.

Is the increase in Fy significant?  Seems to me that the EBF is an in-line fuse that protects the seismic circuit; just in case we get a short circuit in our seismic load theory and the real loads exceed what we think they are.

The other branch to the thread is that sometimes we have to shoot the engineer and get on with production.  This is not meant to flame anyone, just that I enjoy how discussions on the list cross back and forth over the fence between theory and practicality.  I know engineers who reside on one side or the other of the fence and never cross, but I like those who can walk the top of the fence or hop from side to side as they go.

Bruce Hopper, P.E.

USKH, Inc.
2515 A Street
Anchorage, AK  99503