"Michael Daly" wrote in message
...
On 29-Apr-2005, "J. Clarke" wrote:

Concrete for example
doesn't flex noticeably before it breaks so by your reasoning concrete
should never be used as a building material.

Concrete is a perfect example of the problem and one where overdesign is
a problem. Too much steel reinforcement in a small beam compared to less
steel in a deeper beam - the lightly reinforced beam will fail slowly with
the ductile steel failing in tension. The overbuilt beam with too much
steel will fail suddenly and in a brittle manner by failure of the
concrete
in compression.

This is the classic case, but it is NOT a case of overdesign. It is a case
of WRONG design. Overdesign would be sizing the beam twice as deep as it
needs to be, not providing a faulty design.

When dealing with wooden beams, making the beam stronger than called for
is
not going to result in sudden failure with no warning unless the
original
design would also fail suddenly with no warning at a lighter load.

The lighter beam would bend considerably before failure.

But, we are considering overdesign. In this case we must assume that the
design with the lighter beam is SUFFICIENT to carry the load. It is not
expected to fail. Thus a heavier beam would be sufficient as well.

The heavy beam
can carry a significant overload and can cause it's supports to fail
without
warning.

Wouldn't the supports be overdesigned as well? You seem to be considering
loads that cause buildings to fail. In my mind these are things like
earthquake, wind and perhaps snow. With an earthquake if the supports are
going to fail under the load it doesn't matter if the beam is oversized or
not. You are crushed. Likewise with wind. Snow is a different story as it
accumulates slowly, and there you might have a point. But even then I
contend that while an engineering system tries to be balanced, in practice
there is enough variation in materials and fabrication that it is impossible
to be 100% certain how it will fail.

You can't look at a building by considering its components individually.
You have to look at the entire structure as a system.

Sure, and what if the overdesigner does this and overbuilds everything?

I would like you to quote the statute which makes it a criminal offense
to
build something stronger than is required.

If an engineer or architect is responsible for the design of a building,
they are required to ensure that it does not fail in a manner that does
not
give warning (i.e it must fail in a ductile manner). If the design of one
component results in an unexpected failure, whether from over- or
underdesign,
this results in professional liability. Maybe not the Code of Hammurabi,
but
there are still legal consequences - such as criminal negligence causing
death.

Mike

Perhaps you can quote the regulation that states this?
Also, give us a case or two where overdesign has resulted in criminal
negligence causing death.
If they exist you should be able to cite one or two examples.

-Jack