Author Archives: Will Truax

About Will Truax

I'm a timberframer and preservation carpenter, and regularly work on Covered Bridge restoration projects. Bridgewrighting can be a tough row to hoe, for a myriad of reasons. From scheduling issues to differing opinions and philosophies on what is appropriate in methods and materials, to multiple jurisdictions still not sufficiently vetting bidders resumes - Which is to say, just because a company is on that state approved list and capable of building that seven figure overpass, this does not mean they are capable of restoring a wooden bridge... So, I have much to say about all this and more - And despite my tough row observation, I promise not to whine.

Light for the Bridge & Roofs for the Girls

A return to history this go…

And an exploration of a funky bridge now almost one hundred and thirty-five years gone.

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This image from the Robert N. Dennis Collection of Stereoscopic Views is seen here as a courtesy of The New York City Public Library and the Digital Public Library of America

The roofed sidewalks on this ornate example “Village Bridge” would have at least twice daily protected some of Lowell’s Mill Girls from the elements on their way to and from their long demanding shifts.

The following video photo gallery, primarily showcasing images taken by child labor activist Louis Hine is seen here as a courtesy of Selena Marie Perez.

Do bear with me for the few coming days in that the current gig has me tripping through Lowell Mass with regularity, though with this last month being the depths of Winter, stops in the shop are either side of Sun’s up and don’t allow for my taking the few additional photographs I’d like to include in the entry.

Do click back after the coming weekend and I’ll add those, and what is known of this one of a kind crossing, and conjecturalize a bit about the funk in its unique details.

Meanwhile, wonder after those details and this through-truss uncovered allowing us to see if we might arrive at like conclusions.


A Trace of Tears as Brilliance Fades

I struggled with this month’s entry like maybe never before, not in the typical missing muse lack of a starting point way, but in the how a recent entry was about missed opportunity and how I have spoken to loss driven by the very happenstance I am about to lament in a prior entry.

It was with reminding myself that one of the parallel intention’s of this weblog is to share and put forth the notion that Bridgewrighting is a continuing trade, one that requires nurturing both in a growing understanding of this fact by the engineering and wooden bridge communities and in interested members of the general public – and with that, a hope to incentivize a continuing stream of up and coming practitioners into our fold.

That coupled with the thought that this most recently squandered opportunity is like no other to unfold in our lifetimes, had me quash the thought that I would again be beating a dead horse.

The allied trades I practice, Timberframing & Bridgewrighting, were for a time briefly lost. In those years which slipped by with few or no practitioners, vast amounts of information, everyday information so seemingly mundane that few thought to describe it in written words, was also lost. This body of information largely existed in the form of a workaday hive-like storehouse found in the minds of everyday practitioners. It left us with them, slipping into oblivion with those minds no longer being asked to share their depths of understanding and then, as these individuals slowly slipped away, their insights, their once shining light was likewise slowly extinguished and also passed out of being. This is continuously driven home to me in the practicing of both of these trades long enough now to have borne witness to a slow reawakening. In the last thirty years, much has been derived and revived, through research and in a growing understanding of historic example. That reawakening yet unfolds and there is a growing determination amongst today’s practitioners that this body of knowledge, this once faded brilliance, will not be and must never be, lost again. The opportunity lost this go is the replication of a bridge which was to the North American Timberframing Community among the greatest of timber works to be seen. For many in this community, this construction was a built heritage pilgrimage, a must-see somewhat akin to Chartres, the Parthenon or Pont du Gard. I have spoken to this bridge in a number of entries. The bridge about to be replicated is the once mighty Blenheim.

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This Public Domain image of Van Gogh’s Grieving Old Man – Trauernder Alter Mann – At Eternity’s Gate – 1890 Oil on canvas completed in the closing months of his life while he was recuperating in the asylum at St. Rémy – Is used here at the courtesy of Wikimedia Commons

The aspect of this opportunity which is lost is how the framing of the new Blenheim is to be executed not by a highly skilled crew of Bridgewrighting savvy Carpenters, but by a robot. Gone is the opportunity this massive project afforded for trained Bridgewrights to share their knowledge with up and comers in the successive time-honored Master to Apprentice way such methodologies have been passed forward for millennia.

Let’s put aside the seeming absurdity of executing a historic replication with a robot. My point as always is that if we are to perpetuate this skilled trade, the requisite is that we have practitioners sharing their expertise in the practice of those skills. A robot does not share and I’m none so sure one can reasonably replace a group of skilled Bridgewrights.

Do not take what I am about to say as a Luddite-like blanket condemnation of an automated CNC computer-driven approach to timberframing, far simpler frames are obviously doable with this technology. My opinion is more practical and Bridgewrighting specific than that. While CNC is hugely efficient at producing multiple copies of the same piece over and over again, and such pieces do exist in this bridge in limited quantities, (Wind Bracing) major sub-assemblies like the Trusses and Lateral Bracing systems were and are, for good reason (Camber) typically scribed. This is because there are subtle changes in Lateral Brace shoulder angle from panel to panel, meaning these are compound cuts with shifting angles from one set to the next, or even from one end to the other, driven by the attitude of the Ties and their relationship to the changes in the inclination of camber along the spans length, (Camber is not a constant and perfect radii, this is a variable, which changes from panel to panel) there are slight changes in length in successive panels with a truss’es Braces and Counter Braces. These changes need be accounted for to develop camber and ensure necessary full bearing proper fit, but in some panels these changes in length and angle(s) of intersection are so subtle as to seem hardly worth mathematically predicting. Such running of the numbers in this morphing geometry being necessary to program a computer-controlled robot to fabricate subtly dissimilar pieces literally removes all advantage from a CNC type approach in bridge framing. Or worse the subtleties of slightly shifting compound angles and lengths are lost to ignorance – I’ve never seen a set of drawings which acknowledged and quantified this camber driven phenomenon. Drawings are typically kept simple for ease and clarity. Camber is most often specified as a target rise at mid-span and the development of nuances and subtleties in the fine details in achieving that end have long been left to the Bridgewrights chosen.

That said, if full blown, every last detail CAD drawings are necessary to a CNC effort in executing the framing of a wooden through truss and the design engineer does not create them, who does? Will it be a CAD Draftsman steeped in the deep knowledge required to fully understand long clear-span joined wooden bridges, a wooden bridge professional? Or simply a tech in the employ of a factory.

Furthermore, wood in the form of timber is unlike those other materials CNC efforts typically manipulate. Paradoxically, while easy to work, wood always retains its organic nature, try as you might to mill out like copies. Bow and Wind (twist) and tensions released in the milling process will result in not insignificant variations, variations which simply cannot be reflected in CAD drawings.

Add levels of complexity to milled timber like those found in The Blenheim, Joggled Posts, forty foot Arch leafs, crippled Counter Braces interrupted by an encased Shear Block joined triple Solid Timber Arch in the taller middle truss, Bottom Chord Lams with multiple Daps along their length and Bolt ‘O Lightning tension splices at either end, and these organic variations will be even greater and hold greater challenge.

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The interwoven complexity of The Blenheim was captured in this image taken just shy of mid span – This photo by Jet Lowe, taken just seven years before an unknowing storm  almost erased an underrealized bit of heritage is seen here as a courtesy of the Historic American Engineering Record and the Library of Congress

Historically, timber trusses in bridges, industrial spaces, and public buildings saw the timber joinery within them cut to a far greater level of precision than that found in common structures. In any timber truss and most notably in Bridge Trusses, a load is imparted and conveyed from mid-span to abutment, from panel to panel, not simply through the timber in the truss-work, member by member. When you get down to the heart of it these load paths are the joinery, bearing surface to bearing surface within that timber truss-work. In the instance of the Blenheim, literally hundreds of bearing surfaces. This is why truss-work was typically executed with far greater care than more pedestrian constructions, any truss’es joint which fails to have hard up full bearing will result in undue and unintended crush of wood fiber resulting in changes in intended target geometry. An accumulation of such crush leads to loss of camber and this to shifting load paths, with loads being transferred in ways never intended.

To my mind, it is not enough that this replication approximates its predecessor in appearance. The Blenheim and Powers’ and Long’s (More information on both of these gentlemen can be found by entering their names in the search bar above) structural design will not be honored if the bearing surfaces are not well cut. That statement being made, CNC fabricated timber frames do not have a reputation of being high-tolerance frames in the timber framing industry and this is to be an effort to replicate one of the more complicated bridge truss types on what was the longest existing two hundred foot plus joined timber truss bridge history left to us.

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The “Encased Arch” in the taller middle truss – This photo is seen here as a courtesy of Library of Congress and the Historic American Engineering Record – Photographed in 2004 by Jet Lowe

This potential in crush and distorting geometry is perhaps of particular concern with a Blenheim replication, being that this “Double-Barreled” bridge holds a unique structural detail in the form of its massive Encased Arch in the taller middle truss. I’ve always seen this single Arch in the middle truss as part of Powers’ genius, (Outboard Arch ends on less than properly maintained examples sometimes suffer over time  from the collection of leaf litter on them where they join the masonry Abutments, add to that water leaks in the siding and…) keeping the Arch ends as protected from the weather as possible is hugely beneficial though does demand a Powers like level of precision in the execution of the joinery, particularly in the two outboard trusses. Of the three trusses, the middle truss is behaviorally very different from the other two and will carry twice the live and dead loads than that of the two outboard trusses. Should crush borne distortions in truss geometry come to pass, unbalanced loads will potentially shift to the far stiffer Arch which will not distort like the adjacent framing. (Crush borne distortions shifting load to a stiffer arch and this unbalanced load potential would be far less of a worry were this but two like trusses.) This Arch, the backbone of this bridge, is also potentially it’s Achilles Heel.

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The Arch rises up and kisses the Top Chord at mid span – This photo is seen here as courtesy of The Library of Congress and the Historic American Engineering Record – Photographed in 2004 by Jet Lowe

Scribe Layout without question remains the most efficient approach to wooden bridge framing, with such approach, dimensional variation, bow and wind, and changing lengths and angles needn’t be identified and mathematically quantified, they are simply dealt with in real world conditions. This is not simply my opinion. It is a demonstrable truth, and the reason why wooden bridges were the last bastion of scribe type timber layout right through to the end of their common era of construction, better than a full century after scribe layout was abandoned for most all other timber constructions.

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This bridge stood as one of our Nation’s Built Heritage masterworks – This photo of it is seen here as courtesy of The Library of Congress and the Historic American Engineering Record  – Photographed in 2004 by Jet Lowe

So I find myself again grieving for the Mighty Blenheim, though this time not for what once was, but for the ironic opportunity its loss afforded in the form of a baton of knowledge to be handed off and with that, the shared understandings which may have been found in the day to day demands of replicating one of America’s timber masterworks. Sadly, neither will come to pass.

All this is part of the fading brilliance in what might,

nay, what should have been.


Waxing Philisophical

One Size Fits All – Does this phrase fit any reality anywhere?

From this Preservation Carpenter’s perspective this beyond silly never appropriate, never fits turn of phrase, works no better with Preservation philosophies than it does with articles of clothing.

Circumstance reasonably drives what is appropriate in everything we do and in every choice we make. A circumstance sometimes overlooked in the preservation of historic wooden structures is oddly enough the type of wooden structure being preserved. And I am not speaking to how or when a construction was framed, I am speaking to what its utilitarian purpose was and is, and accordingly, what forces and loads it will be asked to bear as it continues on in time in its intended purpose.

I was reminded of this while recently in attendance of the Timber Framer’s Guild conference in Saratoga Springs New York. This reminder came in the form of a parallel perspective I had somehow never before considered, a perspective driven home to me when sitting in on a presentation Jim Kriker of Rondout Woodworking gave on his ongoing work in preserving the famed Hudson River Sloop Clearwater. ( I happily experienced an in-process tour of the Clearwater several Springs ago while helping Rondout with a mill project  – I’d helped Rondout  with another Up & Down Mill in years past, this go, my involvment was in part to free up a Rondout team member to work on the Sloop in its limited off-season) Something Jim said during his presentation drove home how partial replacement of any section of a wooden boats framing is seldom the choice made, pieces are most often replicated and replaced in total and only occasionally by adding new joinery to the mix. This being, in particular, the case in wooden boats which serve as passenger vessels which are subject to the inspection regime that service demands.

This differs greatly from most preservation efforts where seen as chief among the aims in preserving any given historic construction and returning it to structural soundness is minimizing the amount of “historic fabric” removed to achieve that end. And towards that end, individual framing members often see bad sections removed and these are pieced back together, this often at effort and expense greater than what might be required to replace that individual piece in total. That additional expense is seen as worthwhile in that it keeps the structure as close to its original state as is possible. This both to honor the structure and the people and circumstance which has left it to us.

I have often been involved in such efforts, stitching compromised framing back together in replacing rotted section with intricately fit Dutchman and other joined carpentry repairs, whole replacement ends Scarfed onto sound segments of timber components and even removing rot in hollow sections and replacing such lost section with a matrix of rods and epoxy. All this to both honor the building and the Carpenter whose work left us the building we work to leave to the future.

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Here is seen a small section Dutchman in a compression member / Arch Leaf – One captured by the adjacent Post and its sister Arch and the Bolt that will couple all three pieces – Circumstance used to ensure that bending under load and stress on the bond in this repair is completely contained, this with a measurable expectation that this Arch will convey loads as it always has

In most typical constructions, houses and barn’s – The deciding factor in such approach is one of budget, a building’s significance or how structural repairs might affect a historic buildings value. Seldom if ever is structural purpose and behavior taken into consideration when considering approach and philosophy.

I’ve occasionally seen those who hold “Fabric” as the everything and the end-all measure in any Preservation efforts success, point at wooden truss restorations in contempt for failing to retain potentially savable fabric, or in measuring success or a perceived lack thereof, in percentages. And with the same eye they would measure such an effort on any other type of timber construction with no regard as to how one structurally works and behaves as opposed to the other.

This is neither reasonable nor is it in any way even sensible.

The reason for this is Tension Joinery and the almost complete lack of it in most typical timber-framed constructions. True tensile joints ( those intended to deal with constant tension ) are almost always limited to Tie Beams and are meant to deal with roof thrust. ( thrust that is also typically in part resolved through other means within the framings configuration ) The only other tensile loads seen in typical framing are not constant but only cyclical and are borne of shifting wind loads and the Wind Bracing emplaced to resolve this and how it effects the adjacent framing.

This would also be because by far, most of our standing stock in “typical” historic framing, lack any Clear-Span Trusses, such Trusses are almost completely limited to public buildings, such as Town Halls and Churches.

Bridges, however, are by definition Clear-Span Trusses, and in most Truss Types many of the pieces within a Truss’s framing are in tension. And the loads they are subjected to are all of those asked of the typical frame with multiple direct load paths to the ground, ( shifting snow and wind loads and the moving live loads they are constructed to house and bear) and additionally the completeness of their own weight / dead load and the heavy rolling loads a Through Truss is designed to convey.

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There are exceptions to every rule – Here is seen a new tension splice in one of a set of paired Posts – Tension varies from panel to panel in a bridge truss, the load increasing in every step away from midspan and towards shore / Truss Terminus – In this instance the Engineer of Record determined this one’s position allowed for this Scarfed replacement end – All but one of the other compromised Posts in this effort were replaced in total

Replacing lost section in a tension member of a truss is far different circumstance than is that of replacing such section in a compression member in a typical timber-frame. In most instances, it simply cannot be done without diminishing the capacity of the Truss. As an impossible to ignore example, Bottom Cords are the primary tensile member within a truss’s configuration and are made up of multiple laminae, each spliced together to create the length necessary to complete the required span, this almost without exception means there is a tension-splice in one of the lamina in every panel in the truss. ( the exception to this being the four end Panels ) Meaning, if one were to only remove rotted section, this would require adding two tension-splices to the mix and doubling the number in two panels, this both giving up redundancy ( in two lamina truss types giving up all redundancy ) and without question diminishing capacity.

Though the loading of the framing of Wooden Boats and Wooden Through Trusses is almost wholly different behaviorally, their service shares an obvious commonality. And to my mind that commonality and the required fail-safe in safety that is necessarily interwoven with their service, requires a similarity in philosophy in approach to the preservation of both.

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No Bridgewrights

Please pardon the hiatus, the current gig and it’s long commute wrapped around a long day – demands much and additionally, much too much of my time and those days not devoted to it are demanded by other projects, including other writing projects…

So we will now take up the baton with one of the themes and constant wonders this weblog is wound around.

That being how will we, in the unfolding present and the unpromised future continue to perpetuate this trade? The reality of this is that for the trade to carry forward, there must be work for those who have interest in it to engage in, so those who have mastered it can share those unique skill sets and the nuances and subtleties that separate it from its allied trade of Timber Framing to up and coming generations of practitioners.

This work is found in two forms, the rehabilitation and restoration of historic examples and occasionally with the replication of the loss of one of history’s examples. Such loss is sadly borne of tragedy, be it the whimsy of raging weather or the raging stupidity of a destructive personality. The ironic upsides of such loss is the refusal of some to accept such and their demand that what was stolen, be returned to them. Borne of this refusal and the demand it spurs are these historic replications.

And this ironic upside is key to this perpetuation of knowledge that can carry this trade forward, there is only so much that can be conveyed in the maintenance and rehab of our historic stock. Some methodologies, among these, specialty rigging techniques, what achieving desired camber demands of the layout process, and how approach in cutting joinery minimizes the potential crush the constant and cyclical always massive forces clear span trusses must bear, can only be conveyed in the full blown construction of traditionally joined wooden through truss bridges.


And when a wheel spins and spins well, I am admittedly confused by the never ending drive to reinvent that wheel.

Joined timber through truss bridges are not simply proof positive of the service life of wood as a material. Our standing almost two century old examples also provide to us a stunning example of the suitability of wood to wood joinery for this purpose.

The occasional new builds of covered wooden through truss bridges are invariably designed with nontraditional connections. Whether the driving of the decisions creating this dynamic are borne of a wish to reduce cost by designing a construction any typical general contractor can build or if this is an aspect of how few structural engineers are trained in wood and fewer still are trained to understand wood to wood joinery, or if this is simply lack of familiarity and failure to research or liability driven fear, matters but little.

New Builds of traditional design will seemingly never again come to market in numbers which might help sustain our specialty trade and convey our chain of knowledge into the future.

Sustaining this Trade is then in large measure dependent upon future Replications.
 

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Whites Bridge was senselessly lost to arson 7 July 2013 -Photo courtesy of The Library of Congress and the Historic American Engineering Record – Photographed in 2004 by Jet Lowe

So it was with some sadness that I came to understand that one of the replications currently in the offing saw significant changes in design before being let out to bid. This being to my mind particularly sad in that this was a rare truss type (of which there is now but one surviving historic example) and a truss type which can be described as a Bridgewrights truss, being that it is ripe with and wholly dependent upon, complex timber joinery.

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Whites Bridge and its patent Brown Trusses seen here nine years before its loss – Photo courtesy of The Library of Congress and the Historic American Engineering Record – Photographed in 2004 by Jet Lowe

Some of that joinery was changed in the redesign. Most notably in the Bottom Chord tension splices which now are reliant not on the well executed work of highly trained individuals but on the the easily quantifiable values of mechanical fasteners.

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Brace & Counter Brace Drops double dapped through the four Chord Lamina seen here adjacent to Chord tension splices – Photo courtesy of The Library of Congress and the Historic American Engineering Record – Photographed in 2004 by Jet Lowe

With that, none of the Bridgewrights I am familiar with chose to bid on this replacement. Meaning there has perhaps not only been the irreplaceable loss of this Mother example time had handed us, this formerly Brown Truss bridge, the work of patent holder Josiah Brown and its Bridgewrights Jared Bresee and Joseph Walker, but the ironic upside of a once in a blue moon opportunity to continue to forge a chain of knowledge through it’s saddening loss, is perhaps also lost.


Again, my ultimate aim in all the work I do is not simply to preserve our joined timber truss built transportation heritage but also to preserve the skilled trade that made them possible.

Bids are due on this project within a coming few days and we will soon find out who will be building the replacement. Will it be a group of people well versed in joined timber clear span trusses and their apprentices, people who will take what they learn from the project and convey it into the future?

Or will there sadly be no Bridgewrights? And with another missed opportunity the sadly stunning realization that without a continuum of work to serve as the foundations of our future there may again one day be, no Bridgewrights.


My Metaphoric London Bridge

A tangential slightly off-topic entry this go.

On part of the hows and whys on the road of life experiences and how a long ago project, (though I then had no sense of this connection and what would in time unfold) served quite literally as the very bridge on my career path crossing the void from Timberframing to Bridgewrighting.

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A conjectural drawing by C. Walter Hodges – CC BY-SA Liscense 4.0 – via Wikimedia Commons – I had the great fortune to meet Mr. Hodges as he attended a festival held by the North Carolina effort – He was at that moment happily watching two efforts to replicate The Globe play out on two different continents

What I then saw and still see as an opportunity not to be missed, for the promise it held in sharing a then little practiced (at least on this continent) form of timber layout, was accepting a position on a crew assembled to replicate The Globe Playhouse in North Carolina and the opportunity it afforded to work with its chosen Brit Master Carpenter, Paul Russel.

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Paul Russell explaining the nuances of Plumb Line Scribe in the Cruck Framing Workshop we came to know each other through – A life’s work mentor I will forever be grateful to

The Globe itself was borne of a bit of turnabout is fair play in a story of both cunning and cooperation, One worthy of retelling here, particularly in that it drives home the potential portability of timber framed constructions.

The predecessor of the Playhouse was built in 1576 by James Burbage on leased land. Burbage died twenty one years later in the closing months of the lease. The lease specified the lessee could remove any construction built upon the leased land should the landholder refuse to re-let their land. As an underhanded attempt to steal their building, the landholder simply repeatedly put off renewing the lease until it expired while technically never refusing to do so and then intimated that full possession of The Theatre then fell to him. Burbage’s sons and five fellow members of The Lord Chamberlain’s Company, this number including William Shakespeare, formed a “syndicate” a jointly held company to build and operate a new theatre. To do so they would first retrieve their rightful property, taking advantage of their former landlords holiday absence from the city, they would with their chosen “cheefe carpenter” Peter Street begin dismantling it on the evening of 28 December 1598. They would transport the dismantled frame over the frozen Thames to a newly leased plot of land in the “liberty” of the Clink. They then revamped the frame and the Playhouse and reopened it in the Summer of 1599 as The Globe. Their former landlord petitioned the court for damages, his pleas falling on deaf ears. The syndicate would go onto cooperatively run their playhouse for years to come. It like its predecessor would host the inaugural run of many of times most celebrated plays penned by one of its renowned co-owners.

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One facet of the of the efforts eighteen sides – Note the specifically chosen naturally cranked Plate – This Plate held a crank at either end all the others to follow would have had but one

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This replication was to have in time filled this entire area

As a joiner of wood and longtime admirer of this fellow Will, our languages greatest “joyner of words” I am ever disappointed that there are still those doubters that work to deny Will his works and insist they must have been penned by a learned, well traveled man of a far higher social status. I would suggest genius and natural ability does not know any social status and turn their very argument on its head in suggesting that only someone who straddled both worlds could hold his understanding of trades and tradesman and carpentry and joinery, and I think it plausible some of that understanding came from the part he played in the “theft” of The Theatre and the work he engaged in in helping morph it into The Globe in the late Winter and warming Spring of 1599.

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The frame was to have been embellished with the type of carvings typical to the Elizabethan era

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Naturally cranked Samson Plates were to have topped the Posts at the vertices supporting the timbers carrying the inner galleries

I have time and time again here on the pages of The Bridgewright Blog alluded to how scribe was and is for reason how timber bridge trusses were and should be laid out. The Plumb Line Scribe I came to fully understand on this months long failed attempt (full funding failed to materialize) to replicate The Globe, is the most versatile, efficient and accurate form of Scribe timber layout I have learned to date. I continue to this day to use it and its advantages and to share it with fellow framers, most recently and currently I am teaching this system of timber layout to a National Park Service – Historic Architecture Conservation & Engineering – (NPS – HACE) – Construction Conservation & Training – Preservation Carpentry crew as we work to replicate one of the timber sluiceways at the Saugus Iron Works National Historic Site.

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The efforts flag held the Shakespeare Coat of Arms – In the Globes’ time the raising of the flag signaled to those out of earshot that a play was about to begin – With this play over we lowered the flag to half-staff and returned to the greater world in search of future productions

I would some months later return to my home State of New Hampshire with an old, somewhat simple, though very powerful tool in my kit, and somehow found myself that very Autumn, recognized in the pit in a large group of groundlings by The Globes former engineer and he would call me over the fence.

Though as I recall, that is a tale,  I have already told –

 
                           All the world’s a stage, 
                 And all the men and women merely players; 
                 They have their exits and their entrances, 
                And one man in his time plays many parts... 
                   
                     As You Like It - Act II Scene VII

Remarkable

 

Typically I work to vary my entries, to switch up themes from go to go, so as not to bore the readership or disappoint anyone, including myself.

However somehow, just like déjà vu all over again, just as happened last month, another historic wooden through truss, this time rehabbed not a decade ago, but literally at the dawn of this one, has been removed from service.

My continuing ire about this oddly continuing story, is not so much about how this came to pass. (from my perspective, this is less than surprising) It is more about how it might be possible, absolutely no one is asking why or pointing out the absurdity of it all.

Part of my incentive in writing this web-log, and likewise, part of why I engage with wooden bridge enthusiasts through “social media” is both to lend others a view to their interest from my inside perspective, and to also lick a finger and test the winds. This to try to understand what it is aficionados of this aspect of our built transportation heritage bring to our table.

Remarkably, what I seldom see in this community is anyone asking why. And the why in why is it joined wooden through truss rehabilitation’s are sometimes awarded to the wholly unqualified is a beyond big why.

Likewise the design of such rehabs executed by firms with zero background in such structures is equally absurd. Yet seldom, if ever, does anyone ask why in either circumstance.

I see contracting a construction firm that specializes in building concrete deck bridges, (simply because they know how to bid public works projects and are silly enough to think they’ll be able to work it out as they go along) to rebuild a joined timber truss as akin to dropping off a car in need of a transmission rebuild at an appliance repair shop.

I’ll not be apologetic about pointing out how patently absurd it is to point a crew of concrete form carpenters at something as complex as a joined timber truss. Wholly different trades, different tooling, different skill sets and a far differing knowledge base.

The only thing about this sad reality that is remarkable is the wonder in how it is possible this both continues to happen and how it is possible next to nobody is asking why?

 

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Bridgewrighting is advanced carpentry requiring precise high tolerance fits to avoid crush of wood grain under load and distortions to intended geometry in truss-work

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This specialist branch of carpentry requires specialty power tooling and the skilled use of hand tooling once standard in the common era of wooden through truss construction though now little used

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A Trait de Jupiter / Bolt ‘o Lightning multiple abutment Bottom Chord tension splice executed by the author – The need for precise uncompromising fit in such circumstance being obvious.


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.


The Most Important Tool in the Kit

With this entry we speak to tools, or at least the simplest and most important of tools in our kit, and the one which therefore allows for the accurate and proper use of all those that follow.

String is the most important tool in any box – It is a line running though time and history and most every building that ever was or ever will ever be. It is the very beginning, and is even now like a living truth and a real world Möbius Strip, a concept ever connected to an end that never comes…

String, in all likelihood developed from a simple tool used to bind items together for storage or transport, to then be used to build snares and traps and then towards its slightly more complex use in defining strait and true, none so long after our long ago ancestors first pounded and separated natural fibers apart and then twisted them back into cohesion and a potentially unending bit of cordage. This perhaps within generations of that first great leap forward.

All this development coming about long before recorded history. How much time had or has since passed before the first human mind noticed a taut line was strait and then went on to run a string through powdered charcoal with the intent of marking a strait line on something he wished to straiten and to then affix a line to Batters is something we can never know.

It is fitting that those beginnings are yet still just that, the beginnings of most any construction – It all begins with a taut line and Batter Boards, plumbs and the snapping of lines.

My focus on it as still being primary amongst the many tools we have since developed is in part to do with my traditional approach/es to timber layout, though in truth this goes back to my first week in my first carpentry job, in being taught the proper way to string a line and my asking my then mentor who it had been who had taught him the technique he had just demonstrated. His eyes acted almost as a line that day as they belayed the thoughtful recollections and truths spinning in his mind as he thought about it a moment, then he simply said “Well hell, I don’t know, that goes back to way on before the pyramids”

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This image of a Merchet and its companion Plumb is seen here as a courtesy of Wikimedia Commons

In part this focus goes to my primary chosen system of timber layout being Plumb-Line Scribe. Though no matter the chosen layout,  (Square Rule or Scribe) I am datum-dependent. I almost without exception snap lines on every stick, more often than not I do so on all four sides. These lines physically represent two perfectly perpendicular planes of reference.

In Square Rule these snapline planes of reference are used to accurately cancel out bow and wind and to overcome any lack of squareness not achieved in the milling of the timbers, as well as lending reliable accuracy to an organic and imperfect timber in the layout and shaping of timbers to chosen mathematical constants at each of their connections. In Scribe Rule these snaplines likewise are used to cancel out bow and wind as each timber is lined out and are then used to place each timber into scribe layups aligning the two planes of reference to Plumb and Level, this often over a lofting floor on which is drawn a full sized diagram, itself described with snaplines, pinged not with a line enveloped in charcoal or chalk but one dampened with ink. Upon such placement in these layups timbers and the inconsistencies (unlike the smaller pieces of wood found in benchwork, timbers cannot reliably be milled strait and true – Timberwork requires systems of layout which therefore deal with those expected and natural inconsistencies) found in their surfaces, are scribed to each other, often with the use of a Plumb-line used to gauge those inconsistencies.

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Note the Level Mark adjacent to the 6″ Level – It is from that mark that the Datums are unwound – It is with both the Datums and the Level Mark that the timber is placed in the layup over the Lofting Floor – This allowing use of the Plumb Line to covey quantifiable information from each timber to the other

A snapped line, like a line on paper or a computer screen can also be used as a base line from which to develop the geometry to layout any required angles or an Arch or a desired radius or as a control line from which a trusses camber is re-conditioned in a bridge rehab/restoration or developed in a new build.

And in all forms of construction, lines then go onto be used all through the assembly and erection process as a constant reference to insure things are both strait and true and plumb and level.

Though recent advances and circumstance will sometimes demand a laser be the line of choice in the field, reels of string, be they Dry or Chalk Boxes or Ink Lines, will forever and always be, the most important of tools in our kit.


Daps – Keeping Complexity Simple

More of joinery and joints, and the simplest of our intentional intertwinings of wood in the joining of the timber constructions which hold our roofs and roadways up. This being the less than little discussed and oh so under realized – Dap.

And part of that just might maybe be, that a Dap is a joint so simple that the term the uninitiated use, that term most “lay-people” use to describe timber joinery may fit it almost perfectly. A Dap is a but a “notch”, that and that alone, a strait forward and simple notch.

Though in most instances a Dap’s seeming simplicity is multiplied and compounded towards complexity and the solving of structural requirements in multiple ways, (often quite literally, imparting and conveying loads in multiple directions, or providing a load path to turn a corner, the Dap is often the change of direction load path) by being used in reciprocal fashion. Two Daps, each receiving an opposite other, in a sort of simpatico structural handshake.

Though not exclusive to Chord connections, the most common use of Daps in bridge framing is in Post to Chord connections, those very connections which convey loads from one truss panel to the next panel in the chain. In this circumstance they hold a secondary structural bonus in quite literally keeping the joint and all wood to wood contact to an absolute minimum, (typically the depth of reciprocal Daps are dictated by the square inches of interface needed to convey the loads asked of it while avoiding crush in the side grain surfaces within the joint) and simultaneously and to huge advantage maxing air flow around joined timber in the truss-work. This a particularly important advantage at the Bottom Chords where gravity typically draws the errant and occasional leak in a bridges cladding. Minimized contact and maxed airflow help insure a very minor leak, fails to compound into a problem requiring complex repair.

In process

In this in process Truss restoration image – Find in foreground left – Bottom Chord Lams at truss terminus – These joining the Posts with reciprocal Daps leaving space between the Chord Laminae for air flow and quick evaporation

Daps are likewise also occasionally used to convey tensile loads in Counter Braces, both in area variant Long Trusses, and most strikingly in Paddlefords, both examples have been explored and expounded on here on the Bridgewright Blog.

Paddleford intersections

Daps aplenty in this Paddleford Truss image

In more typical joined timber constructions simple Daps are and were, at least in my opinion, sadly underused.

Two notable exceptions to this rule are the striking polarities of historic English and French roof framing systems. To somewhat oversimplify and nutshell these, English roof systems often include Common Rafters over Butt Purlins joined to Principal Rafters – The French tradition (likewise only often) holds Purlins over Principal rafters. In both traditions the over-riding pieces join those that carry them with shallow Daps, or occasionally a two tiered variant Dap often known as a Cog & Clasp.

Blochet-charpente

An illustration From The Practical Dictionary of Carpentry – Joinery & Framing by Justin J. Storck published in 1900

Strangely and almost regrettably, when mother country typologies influenced framing tradition here in New England, (see Overnight Turn on a Paradigm) neither Common Rafter nor Common Purlin roof systems override their support structure with shallow Daps. Both systems are found here in regional pockets, and in both instances, be it Rafters or Purlins both are framed co-planer with the Principal Rafters or Purlins which support them. And this is where the regrettably plays in, these framing traditions were explored in a number of books which have heavily influenced the timber framing revival, and these have in turn driven a predilection for co-planer framing in our revival.

This is almost paradoxical in that designing timberframe constructions with secondary systems overriding primary carriers, be they Rafters and Purlins or Tie Beams and Summer Beams, helps to avoid the three and four way connections many work to sidestep as we design. And it does so with architectural elegance. Beyond that framing with overriding, and thusly continuous Purlins and Joists always also makes for more robust and stable frames – And is this not what we all work to do as we join timber?


Model of Improvement

I had long heard of a model of Col. Long’s Truss in the collection of the The New Hampshire Antiquarian Society, and long had it in mind to arrange a visit as part of research in piecing together my multiple blog entries on the Colonel and his Truss. Though I did not work to do so until coming upon this curious passage in an article titled – An Hour in the Antiquarian Room in Vol XXXII No. 1 of The Granite Monthly, published in 1902.

That initial inquiry to the Antiquarian Society was spurred by some seeming confusion found in the passage, (none of the Childs brothers have or had C.B. as their initials, nor where any of them still living in 1902) and a curiosity as to if there was any possibility that the Society perhaps also had in their collection a model of a Childs truss.

As it turns out, it was a Childs (likely Horace – visit the search bar to the right for information on the man and his truss, or for greater information on the good Col. Long) who donated this Long Truss model to the society, this sometime in the 1870’s. This would stand to reason being that Horace was a cousin of the Colonel’s and his bridge building firm was counted as among the earliest of those named as agent and sanctioned to build Long Trusses, and such a model would have been a useful tool in selling bridges of this truss type.

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Col. Long’s Bridge – The Model fits in its box like a hand in a glove

It was a rare thrill to examine the model, which is truly joined with well executed wood to wood joints and holds features I have not yet seen (such as the upper lateral bracing details, and the thrust blocks on the terminal ends of iron rod wind stays) on any still standing Long Truss bridge. It was also an honor and a privilege to examine this tiny construction, it being perhaps wrought by, and likely held by the hands of one or both of these storied bridge truss patent holders.

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The Bridgewright Blog would like to thank the NHAS / Hopkinton Historical Society for their willingness and cooperation in providing access to this rare piece of both area and wooden bridge history.

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Genuinely joined and richly detailed