Where's the engineer? - was string seating - was bridge caps

[Allan L. Gilreath, RPT]

Ron & the list,

as anyone measured this bridge pin "heave" with a height micrometer?  I
suppose it would do as well to measure the change in the height of the
bridge from the soundboard and the change in the crown.  I'm going to run a
few of these measurements myself but it may take me a while to come up with
some good empirical answers.  I have another question on mensuration but
I'll stick tat in a separate post.

Allan
Allan L. Gilreath, RPT
Assistant Director - TEAM2001
July 11-15, 2001 - Reno, NV
agilreath@mindspring.com
http://www.ptg.org/conv.htm
Director: Laura Olsen, RPT
Assistant Directors: Allan Gilreath, RPT - Gary Neie, RPT - Dale Probst, RPT

-----Original Message-----
From: owner-pianotech@ptg.org [mailto:owner-pianotech@ptg.org]On Behalf
Of Ron Nossaman
Sent: Friday, April 13, 2001 6:29 PM
To: pianotech@ptg.org
Subject: Re: Where's the engineer? - was string seating - was bridge
caps


>Hi Brian,
>              Side bearing per pin is probably less than 10 Lbs. One post
>suporting 8ft ft of fence in a 50m.p.h. wind will add up to tons of
>pressure, dependent on suface area. Plus the rocking effect from varying
>wind speed.  Way more pressure on that fence post than you may think.
>You have to think in terms of the turning moments of force, and it's
>resultant vectors.The string may have 175lbs tension, how ever the angle of
>bearing will determine the actual pressure on the pin.
>Typical ball park, 4-6 lbs down bearing, 8-12lbs side bearing. Just going
>by fuzzy memory. This asuming no friction on the bridge cap.
>The bridge pin may be more predictable than a fence post, knowing our
>weather.  <G>
>Regards roger

Sorry Old Stump (sort of like a fence post, only with bark), but that
string at 175lbs and a 10° bearing will be over 90lbs side bearing on that
pin. A bridge, also, is not remotely like soil. Soil is made up of a whole
lot of small discrete particles (at least we trust them to be discrete),
where a bridge body is a tad more cohesive and will act more like a unit
than a mob of individual parts of what used to be mountains back filling
under any movement. Bottom line -  Bridge pins don't heave out of bridges.
If they did, someone out there would have noticed it, most likely would
have considered it to be of passing interest, and would have mentioned it
to annoy us if nothing else. Not that the fence post in the ground effect
wouldn't have been a first rate analogy had it born the remotest
resemblance to a bridge pin in a bridge, but... But wait! If you act now,
we'll include another full depth post hole at no extra charge - no, that's
not it. Oh yea. There is one rather obvious but interesting similarity.
With all the side stressing and beating both fence posts and bridge pins
take, They eventually get VERY loose at the top, and barely loose at the
bottom.


Ron N