Tag Archives: New Hampshire

Numbers as Great as They Now are Few

A different shake of the box this go, no external wonder over maddening happenstance. This time a glimpse of history and not from my typical perspective, this go we will look at what was, simply because it is so little looked at, and with that somewhat under-realized.

We are about to look at wooden Pony Truss bridges and in the doing, we will explore what was with photographs in numbers greater than is typical of our explorations. Though unlike the allusion of our chosen title, which speaks to how common Wooden Ponies once were and how remarkably those numbers have dwindled, dwindled to a point just short of totality, from untold hundreds if not thousands, to a count which depending on how you categorize the type, which can arguably be seen as countable on one hand.

Old Russell Hill

The Old Russell Bridge of Wilton New Hampshire is sometimes also known as The Livermore

Wingwall

The Russell Hill carried traffic until recent years and is in all likelihood this was the last Boxed Pony Truss Bridge to have done so

Pilaster

The Russell Hill is a Town Lattice Truss – The Pilaster (and the concrete pad which supports them) seen lower right was added to take up load inboard of the compromised Chord ends to keep the bridge in service – The decayed Chords are likely a result of unchecked leaf litter building up between the Back walls and the Truss ends which slowly decomposed into a soil like matter holding moisture borne of rainfall against the Chord lamanie for weeks and months until they likewise decomposed – This an entirly preventable set of circumstance

Pony Trusses were a common solution for short span situations bridging waterways of twenty to sixty feet. In essence a Pony is a Truss short in stature, of a height less than that which is typical of a “Through Truss” – Perhaps the most common approach to weatherproofing Ponies was to “Box” them in, to simply board in both sides of both trusses and to put a little Roof-ette over each of them individually.

This is almost certainly why the landscape is now almost devoid of “Boxed Ponies” – This approach left the Flooring and the Floor Beams exposed to the ravages of the sun and rain and the oxidation and decay such exposure encourages. My educated guess is that long ago replacements were about the need for the regular maintenance wood exposed to the elements requires. With the maintenance regime such exposure demands, Boxed Ponies were in time replaced with Creosoted timber stringer and bent piling bridges and concrete box culverts.

Moose Brook Conwill

The B&M built Moose Brook Bridge seen here while still in service nineteen years prior to its loss to arson – This photo was taken by Joseph D. Conwill – Joseph over a period of decades has visited every wooden bridge in North America, many such as The Moose Brook no longer exist

New Hampshire through a collection of happenstance, climate, Yankee thrift, and the sheer numbers in late examples built by the Boston & Maine Railroad stands as home to most of the Boxed Ponies still standing. One of these was lost to arson in 2004, several years later I helped Barns & Bridges of New England, The National Society for the Preservation of Covered Bridges and NPS-HAER in the replication of its trusses with salvaged iron Rods and Angle Blocks from the original. These were used as full-scale models at Case Western Reserve University in an engineering study and have now returned to NH and are in search of a future home.

Moose_Brook_Axonometric_Cutaway

An As-Built drawing of The Moose Brook created by the Historic American Engineering Record – Seen here as a courtesy of NPS-HEAR and the Library of Congress

Rod Clearance Cuts

10 X 16 X 48 Chord Lams laid down on edge to allow for the cutting of clearance cuts for the Moose Brooks massive Truss Rods

Ready for Placement

Angle Block Abutments and a bird’s eye view of the Truss Rod clearance Cuts – Though a Howe truss differs from most other types in that Iron parts join those of wood this is still necessarily done with the high levels of tolerance required for Truss Framing to sustain intended geometry under the massive loads they are designed to bear

This video, though a bit grainy, does drive home the tolerance of fit strived for in wooden bridge framing. Here, Tim Andrews of Barns & Bridges of New England guides a Truss Terminus Angle Block into place as I lower it with hydraulic assistance

Reynolds

The Reynolds Covered Bridge stood on Blue Ball Road in Cecil County Maryland until 1949 – This Queen Post Pony was built by Joseph G. Johnson the same year he built the Gilpin’s Falls – This Image is seen here as a courtesy of Jim Smedley and mdcoveredbridges.com

Not all Ponies were Boxed, sometimes the choice was to protect the Trusses from the weather by adding a “House” as opposed to Boxing the Trusses independently, whether this choice was made to provide protection to the Floor Beams and the flooring they carried or if this was seen as money better spent, and a more affordable alternative over the service life of a bridge is something the record has yet to suggest.

The Colvin

This image of the Colvin Covered Bridge of Schellsburg Pennsylvania is seen here as a courtesy of Carolyn Williams – I find The Colvin a particularly clever and visually appealing MKP Pony and should you find yourself in need of a short span bridge I’d love to build you a copy

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Crossing Childs’ Living Legacy

Happenstance had me helping out on the rehab of a 19th century cape this past Friday in Contoocook Village, across and up the hill from the Train Depot and almost within sight of my old haunts on the Railroad Bridge. When we wrapped the day, I headed for the far side of Hopkinton to visit the Rowell’s. Both to compare details with those seen recently on Long Truss sister bridges, the Bement and Blair, but also to again put eyes and hands on the Childs’ living legacy.

Some photos from the visit, and observations explored in the details found.

Here is seen the west Portal, the far end has suffered some recent but minor damage. The driver apparently ignoring the impossible to ignore clearance sign, but not the screaming protests of portal trim tearing into the aluminum and fiberglass in the trucks box. Damage thankfully, limited to the Portal, and not carrying on into the Through Truss proper.

Top Chord splices at mid-panel, six laminations, iron spacers, just the single bolt.

Somewhat unusual, the Upper Lateral Braces are in a single plane, one broken and tenoned into the other. More unusual, this system is “Square Ruled.”

(note how the shoulders are truncated down to a common width)

Though many bridges have both systems of timber layout.

Square Rule is typically employed only on secondary systems, Rafters and Knee Bracing. Major systems such as Lateral Bracing, like the trusses, are more commonly “Scribe Ruled,” pieces literally scribed to one another in the direct transfer of information. This to compensate for changes in angles and lengths in the framing introduced by intended camber.

Unnecessary for a Long, these as the “Description” tells us, were built “flat,” with light camber being driven into them during the wedging / pre-stressing process.

The solid encased Arch comes up and kisses the Top Chord at mid-span. (See the July ’11 Archive – Children of Childs, for thoughts on the use of an Encased Arch used similarly on a Long Truss by Nichols Powers on New Yorks’ Blenheim) An Arch being harder to plan and layout than first glance might suggest.

This kiss tells us Horace was well versed in their use and that Rowell’s was likely no one-off or odd experimentation.

A unique detail I’ve seen on no other bridge is this Purlin Post / Purlin Plate system, which support the Rafters at mid-length by providing a load path to the Ties. Built of seemingly undersized timber, this is another suggestion that the Childs Brothers shared understandings learned from their cousin. This framing being kept as slight as engineering calculations allowed, to help keep the bridges dead load as light as was possible.

In some ways, this completes the circle, and in a single generation and within an extended family. The Engineer learns from the bridgewright how to achieve lightness in design and framing, the Bridgewright learns from the Engineer how to max that lightness through calculations, to keep his framing timber as slender as was possible.

Though Long is widely credited with breaking ground in engineering, in using formulas and calculations in the design of trusses, and the sizing of their webs, it is Haupt and Whipple who are widely credited, through their work and writings with disseminating this information to the wider bridge building community. Long’s influence along these lines is perhaps under realized. It clearly began with the publication of “Description” and then through the work of his agents, and their interactions with bridgewrights over widely scattered parts of a growing nation.

Preparations for, and the coming Wason Pond Covered Bridge workshop in Chester NH, are bound to distract me for a bit. We will temporarily suspend the continuing series on NH bridgewrights and patent holders. The next few posts will highlight the Chester activities and all we hope to share and learn from each other there.