Monthly Archives: July 2011

An ongoing adventure at Wason Pond

The adventure continues in Chester New Hampshire, the second truss is in process – Building community while building a Bridge.

Updates posted daily on the Chester Bridge Blog –

http://chesterbridge.wordpress.com/

Post script;

Saturday marked the raising of the Upstream Truss and full assembly of the Bridge and the sheathing of its roof, Sunday also went swimmingly, (literally) with the rolling out over, then the removal of the falsework, (upstream pieces were tipped into the pond and floated by swimmers to shore) then came the lowering and final placement.

Barring a few trip-ups the nine day adventure was in every measure, a complete success. Two highly effective communities coming together to make much happen, and both the better for it.

Photos and an overview of the placement here –

http://chesterbridge.wordpress.com/2011/08/01/untitled-3/

I’ll be playing into framing out and trimming at least one Portal, I do want to see things through, and have come to see Portal trim as something of a feather in the cap, the job’s done now, kinda thing in bridge building. Chester chose some very New Hampshire detailing, with this bridge marking a return to Rockingham County for Covered Spans, I see this as immensely appropriate.

Photos to follow.


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.


Children of Childs

It turns out to be taking more time than expected to turn up substantive information on Mr. Childs and his bridge business partners and brothers, Enoch & Warren. There are plenty of honorable mentions and brief bios, but little in the way of hard information or a sense of just who he was…

Though a prolific builder, with other long span bridges beyond the “New Bridge” pictured in Long’s pamphlet to his credit, (See archive entry – A Name Unknown and a Face to a Name) most notably the former Granite Street Bridge in Manchester, and the famed railroad Triple Bridges at Hooksett Village, and Boscawen’s Rainbow a two span McCallum Truss, these all bridging the Merrimack, and many many other bridges of varying truss types to their credit. Somehow the singular example to still exist is a Long Truss, the Rowell’s at Hopkington. The Rowell’s is an interesting Long variant which has intrigued bridge historians for years because it sports a Childs improvement of encased arches in both trusses. I find myself wondering if they built other solid encased arch examples, and with their railroad contracts providing work over a wide geographic area, perhaps a Childs arch variant Long might have influenced Vermont’s Nichols Powers, who used this same detail in the middle truss of his New York masterpiece, the Old Blenheim.

Seemingly the only other known surviving structure of his construction is the Henniker Academy building, now the home of the Henniker Historical Society.

Sadly and strangely, no examples of his own patent truss still exist here in his home region, though there are a pocket of Childs Truss bridges in Ohio, all built by the bridgewright Everett Sherman. He is said to have chosen this truss type after reading the following announcement in 1882 in the Engineering News and American Contract Journal, that the patents for several truss types had slipped into the public domain, and royalties would no longer be charged of those who chose to make use of them.


Horace is said to have walked long distances in his youth to avoid paying to ride the stage, so he might well have admired Mr. Sherman’s Yankee like thrift.

New Hampshire is still home to a continuing tradition of wooden bridge building and people who specialize in bridge restoration and preservation work. And somehow, in a very real way, I feel that any of us who have ever taken a chisel to a bridge bound timber are all, the children of Childs.