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Re: Fused braces: poor use of term?

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Carl & Nels,

You are correct that the term "fail" is not the best for this situation.
I would, however, suggest that the use of "fail" in this scenario is just
as unfortunate as using the term "fail" when we talk about a beam that has
working stresses that exceed the allowable stress.  In such a case, the
beam has significant more capacity (as it goes into the safety factor and
ductile range), yet we as structural engineers still refer to that as a
failure, so to speak, which does create some confusion among lay-people.

The end result is that the use of fuse in structural systems is still very
similar to the use of fuse in an electrical circuit.  The fuse provides a
desired/predicted limit state in both cases that allow either the
structural system or electrical system to be limited (I will avoid the
term "fail" if it will make you feel better) in a more desirable way that
limits the potential for extremely destructive damage (i.e. collapse or
actual failure in the case of the structural system and
overheating/burning of the wires in the electrical circuit).  I will
certain admit that the are differences between an electrical fuse and a
structural fuse.  In the case of a structural fuse, it is typically still
capable of sustaining a load (i.e. the switch from force-controlled to
displacement-controlled).  On the other hand, an electrical fuse will
actually fail, requiring its replacement before the electrical circuit can
be used again.  I will also point out, to high-lite the similarity, that a
structural fuse (as I have been considering it) will usually require
replacement as well...it is just that the structural fuse does not require
immediate replacement for the structural system to still carry load (in
otherwords, the system will still likely function during the continuation
of the loading event [i.e. an earthquake], but would need to be retrofited
for any future loading events).

HTH,

Scott
Ypsilanti, MI


On Sun, 30 Jun 2002 CarlS95(--nospam--at)aol.com wrote:

> The terms "fuse" and "fail" are unfortunate.  The purpose of a "structural" fuse is to "max out" the force that the system can take, not to "fail."  The connection or member still has strength and ductility;  it is just that the system goes into a displacement-controlled mode instead of a force-controlled mode.  The "fuse" does not fail as in an electrical application, but rather protects failure from occurring elsewhere.
> 
> I recently saw the misuse of the term "fuse" in a recent earthquake.  A water tower had an outdated design whereby the tower is anchored to the foundation using bent plates embedded in a concrete ring foundation.  The anchor plates stretched, buckled, then broke in the earthquake.  The tank lifted up several inches, but did not rupture (luckily).  A local structural engineer reviewing the damage likened the broken anchor plates to a "fuse" that was supposed to fail, and gave the impression that it was a good thing, which in turn resulted in the recommended repair being replacement of the anchors in kind, rather that installing new ductile anchor bolts.
> 
> I'm not an electrician, but there definitely is a difference.
> 
> Carl Sramek
> Los Alamitos, CA        
> 
> In a message dated Fri, 28 Jun 2002 5:01:39 AM Eastern Standard Time, smaxwell(--nospam--at)engin.umich.edu writes:
> 
> > A common usuage for the term "fuse" is describe something that will create
> > a "weak" link in a system.  The intent is that the fuse will allow the
> > prediction of where the system will fail.  This usuage comes from the
> > term of "fuse" in the electrical system.  In an electrical system, as you
> > may know, a fuse is the weak point in the electrical circuit that will
> > fail when the electrical circuit is overloaded.  The fuse 
> > failing prevents
> > the wiring from overheating and catching fire.
> 
> 
> 
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