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#25959 - 03/20/11 07:51 PM Big Wrench Replication
Will Truax Offline
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Registered: 05/02/02
Posts: 447
Loc: Center Barnstead NH

Big wrench, big wood - Species in kind

Full length Chord Lams - Bottoms (Far pair) 10 X 16 X 48 - 640 BdFt - Just shy of One Ton Each



Replication of a Boxed Pony Howe, much like this one, but fourteen feet longer, built the same year, on the same spur, by the same crew.

http://bridgehunter.com/nh/coos/snyder-brook/
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"We build too many walls and not enough bridges" - Isaac Newton

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#26017 - 03/24/11 07:04 AM Re: Big Wrench Replication
Will Truax Offline
Member

Registered: 05/02/02
Posts: 447
Loc: Center Barnstead NH
Quietude...

Is this because this doesn't seem much like timberframing?

It is, and it shares all the same layuots and methodogogies, just like the woodier truss types like Longs and Paddlefords. And has far more in common with TF'ing than say, a Town.

In the instance of a Howe its just that you're sometimes joining iron to the wood - http://twitpic.com/45ndbd
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"We build too many walls and not enough bridges" - Isaac Newton

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#26018 - 03/24/11 07:57 AM Re: Big Wrench Replication
Gabel Offline

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Registered: 11/18/03
Posts: 687
Loc: Georgia
Will as always I'm very interested in your bridge projects. any more pics?

Is that a 2" wrench?
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#26024 - 03/24/11 10:00 PM Re: Big Wrench Replication
Will Truax Offline
Member

Registered: 05/02/02
Posts: 447
Loc: Center Barnstead NH
Gabel - Not really my project, I'm part of a team.

That's a 5" wrench with an 8' extension on the handle. That rod it's on (93 years young) is at mid span and is the smallest of the five at 2¾" - As is common in bridge work, Both the iron and the timber, the Braces and the Counter Braces, step up in dimension from there. The last Rod (the inboard ends of the end Panels) are 3½" in diameter and have 6" nuts.

The wrenches were made by a fabricator neighbor of mine who has been replicating bridge parts for us for years. This time around he also made replicant Nuts - Three of the 6" nuts were stolen while we were in the middle of dismantling.

A shot of both wrenches and the replicant nuts with an original.

_________________________
"We build too many walls and not enough bridges" - Isaac Newton

http://bridgewright.wordpress.com/


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#26026 - 03/25/11 07:12 AM Re: Big Wrench Replication
Will Truax Offline
Member

Registered: 05/02/02
Posts: 447
Loc: Center Barnstead NH

Thought I'd put up an image of the Panel progression -



Here the time is taken to insert multiple panels at mid span, to use the rigidity this creates to then gently condition and stabilize the Chord Lams into the desired geometry and greater camber typically found towards the end of bridge trusses. This in preps to then scribe the end panels in this required and pre-stressed configuration.
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"We build too many walls and not enough bridges" - Isaac Newton

http://bridgewright.wordpress.com/


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#26030 - 03/25/11 08:10 AM Re: Big Wrench Replication
TIMBEAL Offline
Member

Registered: 12/10/07
Posts: 1875
Loc: Maine
Hi Will, some big nuts there. The picture without the scale of the tape are deceiving.

How much camber and will it flatten out once erected and fully loaded?

I have been having fun scribing.

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#26055 - 03/26/11 04:39 PM Re: Big Wrench Replication
Gabel Offline

Member

Registered: 11/18/03
Posts: 687
Loc: Georgia
Wow, that's much bigger than I thought. I see the tape in the first picture now. Wow again.
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#26058 - 03/26/11 07:48 PM Re: Big Wrench Replication
Will Truax Offline
Member

Registered: 05/02/02
Posts: 447
Loc: Center Barnstead NH
Tim – Good to hear your Plumbette is still finding itself in use in your shop. I've been making Drops off & on all week myself.

Ah, camber, often seen as a measure of success and used as a measure of a bridges health...

It really depends on the situation, in the case of the Moose Brook Replication, like Railroad bridges in general and a short one in particular, it's camber was, and will again be minimal at just an 1 1/4”-

With the exception of the salvaged Iron, with it being entirely new construction / framing, and with the scarf free Bottom Chords, I don't expect we will lose all of an 1/8”

Even in the restoration of historic spans, (when you're often recovering from quite severe negative camber) the loss in camber when loaded should be minimal. In the last major rehab we did, the negativity was 10” in the upstream truss and measureable in feet in the downstream. A catastrophic failure shortly before the get go had it sitting in an untypically semi-dry riverbed, this makes for some unusual and severe crush which must be dealt with – An enemy as common as the neglect which created it, yet one recoverable from.



It had Chord Scarfs in every panel – Here we overcome extreme friction in a necessarily tight fit between a Shear Key and two inner Chord Lams.



The resultant 7 ½” camber created with slightly angled (always always in bridge work, you strive for the required full bearing everywhere) Chord Abutments (Butt to Butt joints) and the direct scribing of the Shear Keys to them.



At the reluctance of, but with the cooperation of the Eng of Record, we first loaded the Trusses, (contemporaneous written description and photographic evidence suggests that with good reason this was the order of things) and lost something in the neighborhood of a half inch. We then loosely shimmed the bridge back to the shoring, and kept adding dead load (flooring, rafters and the skip sheathing on them) pulling shims daily as we added more load, and tuned up the Arch Abutments to re-establish full bearing at all joints. Only then did we fit the Arch ends to the Skew Backs on the Bridge Abutments and prepared to load the joined systems.

We prepared to measure deflection and loading in multiple ways for this occasion, comparing a benchmark established at truss loading (another 3/8” as dead load was increased) with the transit readings before pulling the falsework, while at the same time, members of the nearby Johns Hopkins Eng Dept set up strain gauges and the other necessary equipment to collect data –



We then freighted up the bridge with a rolling live load quantified on the scales at the local truckstop. Here we take a transit reading whilst the good Doctor crunches her data.



Forget who came closest in the pool, lost another 1/8” when we cut 'er loose, all told we lost about an 1”- If we were to build the same bridge from scratch, I'd expect way less. All said, we were left with the kind of camber the bridge told us it did once have, but had lost 75 years before when all the floor beams but one and all the flooring had been changed out for mixed hardwood, a huge error adding immense dead load. An error based in the false assumption that stronger is always better.



For the New Moose Brook the documentation should be even greater, it's headed out to the Eng Dept at Case Western Reserve and their new structures lab to be used as a full scale model, they plan to load it up to about 80 kips. When it someday returns to NH (about a year in the lab) it is expected to carry trains again at one of the area RR museums.
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"We build too many walls and not enough bridges" - Isaac Newton

http://bridgewright.wordpress.com/


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#26059 - 03/26/11 09:45 PM Re: Big Wrench Replication
Dave Shepard Online   content
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Registered: 02/19/06
Posts: 707
Loc: Alford, MA
Thanks for sharing this Will. I really like covered bridges. The oldest in Massachusetts was in my grandmother's backyard, used to go there all the time. It burned I think in '93. It was rebuilt by Milton Graton. (sp)
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#26083 - 03/28/11 04:41 PM Re: Big Wrench Replication
TIMBEAL Offline
Member

Registered: 12/10/07
Posts: 1875
Loc: Maine
1/8" in not a lot of sag.

Reminds me of a time when I had miss cut a king post to short, strapped it tight and had lunch, then realized the tie was cranked up. I cut a new king.

Nice contrast between the old bridge and the fix/completed bridge, picture perfect.

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