sci.physics

Robert Clark writes:
> moja...@ (Everett M. Greene) wrote:
> > Robert Clark writes:
> > > On Aug 7, 10:10 pm, Robert Clark wrote:
> > > > Remember pressure increases inversely as the *square* of the area. So
> > > > a joint only 1/2 as wide would experience 4 times as much pressure on
> > > > it.
> >
> > > Correction. That should be pressure increases inversely with the
> > > area, which is as the square of the diameter.
> >
> > Actually, it's 1/4 the diameter squared.
> >
> > > A support half as wide would undergo 4 times the pressure.
> >
> > What does "pressure" area have to do with shear strength?
> >
> > At the extremes, an infinitely short pin can't have enough force
> > applied to it to shear it and an infinitely long pin can't support
> > its own weight.
>
> Measures of strength such as yield strength, ultimate strength, etc,
> are given in units of pressure, such as pascals or .
> That's because a wider structure can support a stronger force than a
> smaller one.

That would be true if we were discussing a column. For a bridge
hinge pin, we're effectively talking about a horizontal beam.
The beam/pin has all the (gravity) load applied along a line along
the top of the pin. There is no "area" to discuss with this type
of loading.