Wheel Truing Tutorial

aka Jobst Brandt wrote:
Tom Sherman wrote:

... I think the concept of pre-stressing has been here often, as
in pre-stressed concrete that has much in common with pre-stressed
spokes, except that concrete cannot support tension and spokes
cannot support compression without being pre-stressed.

That is not entirely true. When a compressive load is applied to
the top of a slab over a limited area, does it not result in tensile
stresses in the bottom portion of the slab below the "neutral axis"?

Bridges and other structural beams have tensile preload rods internally
to insure that the entire beam is in compression even though most of
the tensile elements are in the foot of the cross section.

Actually, post-tensioning is more common on larger structures, since
pre-stressing outside of items that can be made in a plant is not very
practical.

The
condition you cite would cause cracking (failure) but structures are
not designed or loaded that way if they follow prudent procedures and
of course the building code.

Specifically, ACI 318 "Building Code and Commentary".

And do concrete pavement slabs generally fail from fracture due to
tension in the bottom of the slab from a single load, or from
fatigue from many load cycles? The answer should be obvious to
anyone who know about pavement engineering.

They fail for insufficient reinforcement (steel) but they are not
pre-stressed in roads I have seen built other than bridges, and they
were pre-stressed.

All plain reinforcement does for slabs is to hold the pieces together
AFTER the slab cracks. Portland cement concrete will fracture at a
strain where the reinforcing steel is far below yield, and the
reinforcement does little to reduce fatigue stress.

There are some post-tensioned on-grade pavements, but they are rare.
Post-tensioned bridge decks (and floor slabs in mid-rise and high-rise
buildings are common).

Fiber reinforced concrete is not pre-stressed, and the fibers do
increase tensile strength (as evidenced by the fibers increasing the
rupture modulus for a given mix).

That's a composite and I am not familiar with that use. It seems
highly difficult, considering the elastic modulus of stone and fibers
one might use. I suppose asbestos might be a candidate. I don't know.

Fiber reinforced concrete floor slabs (in industrial applications) and
pavements are quite common. The fibers can be polymers or deformed
steel. The fibers make quite a difference in rupture modulus, which is
typically determined by breaking beam specimens in either third-point or
half-point loading.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

Ozark Bicycle wrote:
On Feb 29, 2:32 pm, Tosspot wrote:
Ozark Bicycle wrote:
On Feb 28, 8:13 pm, "Skip" wrote:
Because JB is snotty and pedantic.
Yes, but Jobst also knows his stuff cold and is a true expert on the bicycle
wheel.
You won't find a better "expert".
The above proves that, indeed, "you can fool some of the people all of
the time".
And looking in the mirror I'd agree with you.

Your mirror, your eyes, your visage. :-)

'Twas my point, fooling some of the people all of the time seems to be
trotted out by people trying to fool all of the people some of time,
which leads to suspect very little is believable in this world. Apart
from the fact that GWB was piloting the WTC planes by remote control
with Elvis acting as copilot. This is fact.

On a related note, I've had two driveside spokes fail in around 6,000
miles commuting. One failed at the knee, which I took to be an
undertensioned wheel (I built it), the second went a few millimetre
further up, shearing across the spoke around 3,000 miles after the
first. No signs of rubbing, or other defect, it looks like it just
broke. I'm sure these are up to full tension, but I don't have a
calibrated tensiometer to check.

Any ideas that could be checked without too much complexity? Wish I'd
kept it and photographed it now

I think that is generous criterion.

Jobst Brandt

Jobst,

add an essentail visual action scene for a hypothetical spoke graphic
tutorial?

g.daniels

sure. after insertion then after tensioning, lube and fill spoke holes
and cover 4 flange sides with Finish Line dry lube