Tag Archives: Timber Framing

Appropriate Technology – Appropriate Methodology

Well, things churn, and a turn of events has my ire up – This something measurable as more than “a little”, something beyond a bit more than can’t push it aside, all the same, let’s describe my ire, as up, just a bit…

Many regulars among the readership will be aware that my intent, my work here on the Bridgewright Blog is as much about advocating for preservation of this “Trade” as much as it is an advocacy for the preservation of the historic bridges that are the fruit borne of that tree.

I am a practitioner of two allied trades, Timber framing and Bridgewrighting. Both, seemingly superseded, were briefly lost. In the but generation plus period of time in which both trades had fallen out of practice, (I have spoken to this in prior entries, this perhaps best articulated in Living Memory – And the reasoning as to why best described in Meritocracy) much was lost.

In both instances, in their long running period of practice, too little of the everyday was written down. Though there are some few notable exceptions on the timberframing side, with little of practice preserved in the written record, this break in the chain of day to day practice, of lifelong practitioners passing down the intricacies and the nuances of the everyday to an up and coming body of Apprentices – Much, much too much, was lost.

It is not an ability to look at and understand a patent truss drawing that makes a timber savvy carpenter a Bridgewright. Bridgewrighting is only an allied trade, there are subtle though highly important differences in approach in building long-span trusses. A full understanding of these subtleties being born only of the almost unspoken day to day understandings found in a lifetime of practice, or years in working alongside someone who already possesses a lifetime of doing and has a willingness to share all they know.

All of this of the sense of last months entry, that it is with a simple line that it all begins, that such is the key in unraveling and unwinding the secrets of timber. Of how full hard up full bearing in every joint cut and how to get there is the not so secret of how a knowing carpenter gets a truss to hold its intended geometry. And this continues with an understanding of the material with which we work, with which species is appropriate to the task at hand, with how center, pith and balance and the presence of sapwood effects how any given piece will behave as it seasons, and how that understanding is (or should be) what drives every decision as to how any given piece should be oriented in bridge truss framing and might be used to its greatest potential advantage.

Winding Sticks

Two Framing Squares used as Winding sticks – A black Eagle backed up by a Horizon Board is seen riding the mid-length Level Mark in the distance stands in contrast to the stainless Square in the foreground allowing for adjustment and compensation for both bow & wind in the pinging of snapline Datums

Much was lost, and much of that, with practice and research and perseverance, has been recovered…

Though it is only with regular opportunity for the practice of these skills, and the conveyance of the understandings and nuances that are the bedrock of those skillsets from today’s practicing craftsmen to a coming generation, that there lies any opportunity to pass on either to an up and coming group of practitioners.

And here is where my ire lies, with near miss opportunities lost. And opportunities ill spent.

A new covered wooden though truss was recently constructed, though it was of the dumbed down bolted together type now growing in commonality. It holds no passion, its construction requiring no specialized skills or knowledge base, and so sadly, holds no promise of sharing any. Though this truss was launched with the low tech promise that holds the possibility to share how simple rigging allows the moving of large objects with surprising simplicity and ease. That promise was buried in needless complexity, and even were there the opportunity to relay simple rigging wisdom, it is doubtful that anyone with a passion for this trade was there to receive it.

Un-Stayed Gin

Though requiring now uncommon know-how, time proven Appropriate Technologies are often the most cost effective way to make things done

And sadder still, and none so far from that opportunity lost, an 18th Century bridge rehabilitated but a decade ago and said to now have a full foot of “sag” has just been awarded to a second low bidder – And somehow no mention is made of poorly designed repairs equally poorly executed by people in both instances who had little sense of what they were doing. Instead it is intimated in the announcement, that old wooden bridges, of their own accord, just up and go haywire.

Without either neglect (a lack of routine maintenance to siding and roofing and the removal of dirt and leaf litter from the bridge and its underpinnings) or poorly executed interventions, the time proven service lives of these structures more than suggests that such could not be farther from the truth.


Gleanings from the Grit

There are almost unintentional undercurrents here on the Bridgewright Weblog. Yes I’m intrigued by those we follow, my fellow practitioners in this trade, they in its heyday, we almost entirely from a preservation perspective. They with knowledge in abundance shared by necessity, from Master to Journeyman to Apprentice. We are left to glean what we can from what we might – Most of this is to be found not on paper, but in physical example.

Photo by and courtesty of C. Hanchey

So in this entry we dip the paddle and turn briefly, to follow a parallel current in the study of wooden bridges and bridgewrighting, and through their work, the people who built them.

The only set of Shear Block Joined Long Leaf Yellow Pine Bolsters to have survived the 30's floods & tippings - At the same corner as the Historical Marker

That brings us back to an undercurrent, Railroads drove change and innovation, and though their connection with wooden bridges is all but forgotten, being that this connection held a then almost unique place in straddling the emerging worlds of corporate style big business, civil engineering and academia, it is almost no surprise that railroading’s ties to wooden bridges are well represented in the written record. Part of the other undercurrent we ride is found as we run our fingers though and sift the dirt, the stuff, the sluff – The grit still left to us for interpretation in still standing examples is there to find, despite the passing of time.

What is sometimes hard to see, is that it might just be in the dirt under our nails in which we find much of what we are looking for –

It is tool marks left in long tightly closed timber joinery that no one has gazed into in multiple lifetimes, It is scribed marking knife and awl marks and remnants of layout lines and faded numbering left to us in the cursive grease pencil handiwork of some almost forgotten carpenter, the pride with which he executed his work daily still evident in the elegance found in his handwriting. It is a shear failure, and how the woods grain reacted to it. It is an expected depth of crush created by fifteen decades of constant and massive force. It is how a needlessly neglected leak led to unnecessary failure, and how that failure effected load-paths, and how those shifting load-paths effected the through truss as a whole.

As much or more is to be gleaned in the hands on side of things, as anything we might find on the written page.


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.