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Candi Anderson wrote:

"Hello All-
I need to provide information or details for adding a pinned member to
an existing truss.  Does anyone have information or a lead on the
fabrications/construction specifications for such an item?  This is very
small (on the order of 1" diameter).  Thanks for any help.
Candi 

Candi Anderson, P.E."

Candi,
I'm not completely clear on what you're trying to do.  I assume you mean
you need to either add a piece to augment a deficient tension member, or
you need to add a tension counter to take care of some load reversal.  I
assume these mostly because they're what I know how to do, having done
it exactly once.  I had a piece fabricated with a box assembly on each
end, through which went the two legs of a U-bolt.  The U-bolt was placed
around the pin at each end, the legs placed through the box assembly,
and nutted off and tightened to what we described as "taut" (technical
term).

To elaborate on the box:  my new tension member was something on the
order of 1 inch by 2 inches.  If the dimension pin to pin was 20 feet,
the tension member was maybe 18 feet long.  Across each 1 inch side at
each end I laid a bar, maybe 1/2 inch thick, 3 inches wide (in the
direction of the length of the tension member), and maybe 5 inches long.
These bars were welded to the main piece in the L (giving me a 3 inch
long fillet in four places each end of the tension member.  Across the
ends of the flat 3 inch bars, I welded another piece to make closed 2" x
2" squares.  The legs of the U-bolts ran up through these squares,
through the nice thick washer on top, and nutted off.

If you mean you need to install a bigger pin, good luck.  You'll have to
completely support the truss throughout it's length, somehow remove the
pin, somehow ream out all the connecting members to take a bigger pin
(if you can't make it using higher strength steel, which would be
preferable), and then re-assemble everything.  Major piece of work.

If you mean you need to reinforce a compression member, I'd weld plates
along it.  They could be arranged to bear on the pin if, improbably,
bearing governed.

By the way, on the trusses I needed to reinforce (240 feet long, if
memory serves), the biggest problem was that the existing tension
members had moved around on the pin, and they needed to be shoved aside
to make room for the new piece.  Pancake jacks turned out to be just the
ticket for this work; they are small hydraulic jacks, only maybe 3
inches tall and 5 or 6 inches in diameter.  They had a stroke of about
an inch, but that was all we needed.

Has any of these scenarios answered your question?

Mike Hemstad, P.E.
TKDA
St. Paul, Minnesota  

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