In article ,
J. Clarke wrote:
Michael Daly wrote:

On 28-Apr-2005, Unquestionably Confused wrote:

To overbuild is never a crime

Overbuilt can cause a failure. For example, if something is designed and
built correctly, it will tend to show excessive deflections before
failure,
providing a warning. Overbuilt things can fail spectacularly without
any warning.

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.

The ductile material will bend before it breaks, the brittle material will
simply break.

As for something "designed and built correctly" showing "excessive
deflections before failure", certainly one can design things that way but
that doesn't mean that it's the only correct way. Concrete for example
doesn't flex noticeably before it breaks so by your reasoning concrete
should never be used as a building material.

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.

*NOT* necessarily true.

Engineering for systems under stress, particularly dynamic stresses, is a
_complex_ and _complicated_ subject.

*ALL* the components have to be considered, =both= singly, and in combination.
'Over-building' _one_ component can result in excessive transfer of stress
to _other_ components, Leading to failure of _that_ component under conditions
that are _less_ severe -- as measured for the overall system -- than the
original design was spec'ed to handle.

There are numerous real-world instances of this *exact* thing happening.
One of the easiest places to find them is in the world of home-built, plans-
built, aircraft. Firstly, in general, the 'safety margin' on _any_ aircraft
design is extremely small. "1.6" is typical for commercial construction.
Homebuilts usually are designed with higher margins, because there is more
variability in the quality of construction. However, there are =many= cases
on record, including after-the-fact engineering analyses, where a home-builder
has modified a design -- to =strengthen= some part of it -- where said mods
have led to _premature_failure_ of other areas of the design. Higher "point
stresses" occurred in the modified design, as a result of the modification,
than the original design was designed to handle.