Monthly Archives: September 2014

A Theme and its Variations

Several years back I became highly familiar with The Bement Bridge in Bradford New Hampshire, this in a series of surveys while preparing a Structural Condition Assessment. That hard look was the genesis of a deep exploration of its named Truss Type, and a bit of a bio-exploration of its engineer patent holder, (and tangentially a running theme of an on-going wonder in how someone with no bridge building background might have come to design the complex joined timber truss that he did ) that exploration in large measure unfolded here on the pages of The Bridgewright Blog.

The Bement has recently recaptured my attention with my again working just a skip down the road from it, and with an area historical society recently making available several photographs which predate alterations made in recent decades. Changes structural and aesthetic.

The Bement with its original far more elegant Portal Trim - Image courtesy Hillsborough Historical Society - MPM Collection

The Bement with its original far more elegant Portal Trim – Image courtesy Hillsborough Historical Society – MPM Collection

In again skipping this stone of interest into the waters under this bridge, two ripples surface once more. Who was it who built it, and just what Truss Type is it? Individual Panel components typical to the named type are all there, and I am going to continue calling it a Long, while acknowledging it is a Variant. Many truss types are found in an array of variations, this perhaps driven by a desire to avoid the cost of patent royalties, or as explorations of capable minds guiding capable hands in looking for a better way.

The Bement while fitting the typ Panel component configuration of the type, varies markedly from Long’s patent, both in the number of these components – Single as opposed to double Posts, and not three, but four Chord Lams. Additionally the components vary completely in how they are joined to one another. The Braces and the Counters are reversed in their configuration and their number. And perhaps the most striking variation / departure from the patent are the absence of the pre-stressing wedges at the Counter Braces, a key feature of the type and the Colonel’s patent itself.

Double Daps and a reversal in number and purpose

Double Daps and a reversal in number and purpose

The Counters in the Bement fully join and pass through the Chord Lams in reciprocal double Daps, (simple notches) and do not simply abut the Chords & Posts with one wedged end as is typical to the typology – As if intended to act in tension as opposed to the norm of compression.

I point these features out for a number of reasons, foremost among these being that of a form of kudos for the bridge itself. There are other Long Truss bridges and Long variants still existing, and I have a deep appreciation for their detailing in how they are joined, yet find the simplicity of this little bridge intriguing, and worthy of admiration.

Secondly the historian in me thinks it just may be time to put to bed the oft repeated notion, that The Colonel himself built this bridge. The record does not seem to suggest where this bit of mis-information was first floated, but it is simply that. For Long’s whereabouts for the whole of the year, are well recorded in his work for and travels demanded by his position on the Board of Engineers for Lakes and Harbors and Western Rivers – He was nowhere nearby. And had he been in any way involved in its construction, I think it reasonable to suggest it would not have been a variant, but a textbook (Series of Directions to Bridge Builders) example.

So who did build the Bement? I think it safe to assume it was someone from the immediate area if not a local. There is not a ten mile distance from the Childs Brothers framing yard in Henniker to where the bridge stands, and there had by this time been a multitude of covered spans built all up and down the Warner River for both Railroad and highway use. There were those in numbers in the area with the necessary skills and knowledge to have designed and built it.

The Tie has been modified to carry a Flying Plate, the Rafter Seats now sits abandoned

The Tie has been modified to carry a Flying Plate and the altered Steplap Rafter Seats now sits abandoned

An interesting aside is the sometimes mention to the Bement’s Counter Braces and their joined relationship to the Chords as having similarities to Paddleford’s – The Bement shares (or did share) another even more uncommon feature, one found almost exclusivly in Paddleford’s, that of the Rafters joining the Ties in Steplapped Rafter Seats – Philip “Henry” bridged the Merrimack at Sewell’s Falls (but thirty miles to the east) in Concord just the year prior. (1853) Could our Bridgewright have maybe served on his crew and borrowed a detail worthy of repeating. I find it not improbable, and a smile rising with the realization and the on its head irony, that perhaps a Long variant was modified with influences driven by a Paddleford.

Here can be seen the Steplap Rafter Seats still serving their original purpose - Image courtesy Hillsborough Historical Society - MPM Collection

Here can be seen the Steplap Rafter Seats (Click to enlarge) still serving their original purpose – Image courtesy Hillsborough Historical Society – MPM Collection

Should you need a short span bridge, why should we not build a variation of The Bement, over another waterway, and set yet one more story in motion?