Michael Daly wrote:

On 29-Apr-2005, "J. Clarke" wrote:

Where you run into the kind of problem you describe is when a strong
but brittle material is substituted for a weaker but more ductile
material.

*NOT* necessarily true.

Please provide a case in which replacing a weak ductile material with a
strong equally ductile material results in the kind of failure you
describe. Please include the analysis.

You've made two different statements here.

No, I've made one statement.

If something is stronger, the fact that it's ductile doesn't necessarily
make
it ok. You can change the load regime without entering the point where
ductile failure of the replaced element comes into play.

So in what mode does the replaced element fail? Or are you saying that the
other elements which one supposes to be properly designed will not give
this warning that you describe, that the ONLY element which will give this
warning is the beam that was replaced?

Seems to me then that you need to do something about those other elements.

Buildings of the kind where an individual would be installing or removing
a beam are not typically under "dynamic stresses" to any significant
extent
unless you want to count wind loading. If you want to talk skyscrapers
it's another story, but they typically have little or no wood in the
structure.

I've done dynamic analyses of some pretty small structures. They don't
have to be skyscrapers to have dynamic loading problems.

How small is "pretty small"?

How can it "result in excessive transfer of stress" if the loading is the
same?

The problem is that the loading isn't necessarily the same. Just because
the design load is the same, doesn't mean that the load in use is the
same. If someone overloads a properly designed building element, they will
see
precursors of failure. If the element is overdesigned, those precursors
(e.g. excess deflection) don't show up.

So let's see, it's all right to overload the structure and have it show
"precursors of failure" but it's not OK for it to just sit there holding
the load?

Proper design means that you get
a warning if you have overloaded the structure.

I see. So you're basically saying that your properly designed structure
will give warning if the _beam_ is overloaded but not if the _posts_ are
overloaded? Do tell. Sounds like sloppy design to _me_.

Show us how to make a house fall down by making the headers too strong
and maybe someone will listen.

The poster said that overdesign is never a problem. No mention of
headers.

Read the title of the thread. We're talking about something in the ballpark
of two two-by-tens, not about the effing Space Shuttle.

GET SOME BLOODY PERSPECTIVE.

Mike

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--John
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