Category Archives: Bridgewrighting

Steadfast Against the Storm

I had it in mind to finally post a followup to The Central Bridge entry Friday, I’d been waiting on image accreditation permissions and access to an artifact, a literal lone surviving piece of that long lost bridge…

Then the distraction of this thirty hour April Fool’s Day storm and a bit of news which also crossed my horizon created a need to update the blog’s readership regarding an entry of a few months back, a lamentation entitled A Trace of Tears. The news and need to update is in how the low bidders chosen pre-qualified “timber specialist” has now formally engaged a subcontractor, one that redetermines how the framing of the new Blenheim is now to be executed, being that it is not the same automated manufactory they had enlisted to execute their last new-build.

A_Wall

A Stonewall in the woods standing steadfast against snowfall and time, much like little-known truths, somehow also obscured and almost lost, as if such were likewise buried behind layers of ice and a forest like tangle of trees

The timber framing community is a small one, so I have some sense of the firm enlisted. I do take solace in the fact that the three Trusses and the Tie, Floor Beam and Lateral Bracing systems which will unify them will be laid out and cut by genuine human beings.

I am at the same time bewildered that a pre-qualification process intended to limit bidders to those with deep wooden bridge resumés would then allow any of those deemed qualified, to sub off the whole of the fabrication effort (The very aspect of a joined timber truss bridge build that requires deep experience in know-how and understanding as to the requisite of full bearing tight fit) to a firm which had not navigated that same process. It is an absurdity that flies in the face of reason and fairness and makes a mockery of that process.

Bottom Chord Scarf

The multiple abutment Trait de Jupiter / Bolt ‘O Lightning tension splices specified in the man’s patent and common to Long Truss bridges through to the end of their common era – One of the flawless fifty plus Bottom Chord Scarfs of Powers’ lost Masterwork

That said this Timber Frame subcontracting firm does have a short bridge truss resumé, one limited to single numbers, recent developments which have only come to pass in the last several years since the very storm which took The Blenheim from us. Nor is this outfit a scribe-centric shop. historic practice demonstrates in the form of surviving example, and I adamantly hold to the notion that joined timber bridge framing, is for the need of both practicality and accuracy best laid out with “Scribe Rule” methods, this for all the reasons I articulated in Trace of Tears. I do unhappily understand that that notion is little shared and reasonably not understood by lay-people, nor for reason explored in an archival entry I penned a few years back titled Commonly Uncommon, is this even commonly understood by Timber astute Carpenters should they not be fully versed in both traditional bridge truss practice, and full blown layout to assembly scribe methodologies.

Blenheim's Bottom Chords

In the foreground a now lost glimpse of the beyond amazing Bottom Chords of the Double Barreled Blenheim – In the distance my truck and tool trailer in a stop to pay homage on a pilgrimage driven side-trip on a return home ride from a hired gun timber gig

That solace I find in this development is not only in the removal of the incapable robot, it is also found in the human connection which will undoubtedly unfold. Among those to cut this replication of the grandest of grand joined timber wooden bridges so recently lost to us, will be individuals, who will in the doing likely experience a spark of imagination, and perhaps that spark might help them find the focus to make this allied trade of Bridgewrighting, their live’s calling.

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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 the lengths of Braces and Counter Braces and 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.

blenheim-perspective

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.

blair-boot

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 Chords 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.


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.
 

whites-portal

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.

whites-brown-trusses

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.

whites-bottom-chord-scarfs

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.


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.


Everything with Purpose

The somewhat unsaid case for slopes.

Just to clarify for those many among the readership who have never cut a timber joint – “Slope” is the going term for an angled cut into the backside of a mortise which receives an adjacent member which joins it at an angle, these typically being the common wind or “knee” braces typical to every timber framed structure.

This Wind Brace Mortise now sports a “Slope”

Most of those who cut timber joinery fall into either of two camps, those who cut them and those who don’t. The “don’t’s” have reason – A slope cut at an angle even a single degree too low, will simply not allow for full insertion. This added to there being in most instances, little, if any return on the time invested in (laying out – the cutting is simple) cutting them.

The other reason often held up, is historic precedent, and this is certainly there. Most Brace Mortises in North America lack any slope – Though I am going to qualify this somewhat slightly, by suggesting this, only most, and not all.

I have come upon historical examples, and of two types – Early Scribe Ruled frames do sometimes have slopes. This would be because both the exact placement of the spine of the brace is a known, (this is not true of Square Ruled frames) and the exact angle that the brace joins the mortised stick is also a recordable known, and with that information, it is easier to chop out a slope with a Corner Chisel than it is to bore out empty space with a Tee Auger.

The other instance in which I have seen this is in bridge joinery, and though such is most often scribed, the reasoning for the trouble taken to cut them was not about the information to cut them accurately being a known. It is about not unnecessarily removing “section” – It is for reason about not wasting out wood and unnecessarily weakening the mortised timber any more than need be.

Here we see a replicant Tie Beam with both Through Mortises for the Lateral Bracing visible on this face

Here we see a replicant Tie Beam with both Through Mortises for the Lateral Bracing visible on this face

Some of this is driven by that constantly considered aspect of wooden bridge design, this being “Dead Load” – Timber, particularly in later examples, is sized to the smallest section possible, to make the trusses as light as was possible to minimize “Dead Load”. (though then as now all is /was ticked up in size with a bit of a “failsafe”)

A knowing and careful Carpenter / Bridgewright, is and was cognizant of this, and did / does not let the joinery he is cutting unnecessarily weaken the stick he is joining.

Some of this thinking necessarily goes to the proximity of the joints being cut – Would two mortises in close proximity (should they even be in close proximity?) be better off were one or both cut with slopes?

This broken Tie is temporarily re-enforced for the rehab effort prior to its replacement

This broken Tie is temporarily re-enforced for the rehab effort prior to its replacement

As a bit of an aside, the lack of any slope leaves a void. Without exception, in every brace mortise I have ever opened up, something had moved in, and had brought with it, the stuff and sluff of life. The shredded whatnot for its bedding or its bathroom. This “stuff” often serves as an unintended sponge holding moisture, when that someday comes and an inconvenient leak points water at the spine of a brace, and funnels it into the mortise. This “Sponge” is not infrequently the secondary genesis of a huge problem…

I avoid this void in cutting new barns, (again, both mice and bats bring their stuff to these voids in every barn frame I’ve explored) and in frames subject to weather, like porches and pavilions, and of course – in Bridges


The Curiosities of Miscreation & Happenstance

This piece will be about the multiple curiosities of the current project, and how these say much about Bridgewrighting, though in a way which for some might seem unexpected, or to others even somewhat harsh. Those who click in regularly, will however recognize my frequent allusions to the quality in execution that is common to framed wooden bridges, and why precise fit and full bearing are necessary, and drive that commonality…

Reaching completion in December of 1865, the contract to build The Jericho was to awarded to one Thomas Forsyth of Baltimore, the trade he practiced is said have been that of a machinist. This would seem to be an odd choice in someone to design and frame a bridge. Particularly in the day, this the common era of wooden bridge construction, (there are perhaps more such bridges standing which date to this same decade than any other) a time when the chosen Bridgewright was responsible for design as well as execution, and this Trade was in common practice.

Getting to know this bridge intimately during the rehabilitation process, (a process which avails to those doing it views of joinery last seen by those who assembled it, in this case a full century and a half ago) I have come to believe this curiosity, that this bridge was indeed, designed and built by a practitioner of another trade.

Why would be the wonder, particularly in an area which held much Bridgewrighing knowledge. The nearby Susquehanna hosted large efforts in numbers, and such knowledge would have been shared and without question would have left this Trade in this area the better for it. The first thought that came to mind, was that perhaps Thomas was politically connected, and some kind of cronyism potentially played a part. The second went to the year of construction – This country, with hostilities ending only in the Spring of this same year in the killingest war this nation has ever suffered, had just lost much in the fallen and sadly no longer flowering knowledge of what was quite literally, a lost generation. Was there potentially a war driven lack in ability?

With deeper wonder and exploration, as other entries here on the blog have touched on, this trade was in happenstance and terrible irony, bettered by the exchange of ideas and the networking availed to those building and rebuilding bridges during The War. It secondarily seems more than probable, that coming into the war effort with bridewrighting skills and being assigned to such a company, may well have made that terrible and costly war, a more survivable service than it may have been for the common infantryman.

Though it is left to supposition I have come to believe it may well not have been the certain uncertainties of those tumultuous times which left the call for proposals unanswered by any capable crew. Circumstance suggests that this curiosity was potentially driven by one of these nearby large efforts on the Susquehanna.

But twenty three miles away at the river which defines the northern border of Harford County, just as the Jericho bridges the Little Gunpowder, the waterway which forms part of it’s southern border, there was at that time an ongoing effort we have spoken to here on the weblog, an effort said to later have fifty hand picked crew leaders chosen by Nichols Powers, and working under them, some three to four hundred known quantity Bridgewrights.

The B&O Susquehanna River Bridge - Though a different image, here we see the same two gentleman... This image is seen here as a courtesy of Wikemedia Commons

Two of the fourteen spans of the B&O Susquehanna River Bridge – Though a different image, here we tellingly see the same two gentleman discussed in the Evermore entry – This image is seen here as a courtesy of Wikemedia Commons

This particular effort is shortlisted on my – Where and when would I visit, if I had an opportunity for time travel. (The other effort I would choose, would be that of joining the crews raising the Lintels to complete the Trilithons at Stonehenge) – I’m thinking the Bridgewrights with chops in this area, were both fully distracted and gainfully employed…

Mr. Forsyth did quite clearly subcontact in some Framers, (though of a caliber common to low quality barns and clearly unfamiliar with the demands of Bridge Framing) and he did somehow find someone capable of determining the radius of and the laying out the Arches, though even these are not up to normal snuff.

Not only is there a Lap Joint at every Post on both the inner and outer Ring - This type of atypical tear-out and over penetration is found commonly

Not only is there a Lap Joint at every Post on both the inner and outer Ring – This type of atypical tear-out and over penetration is found commonly

His chosen twists in design are beyond odd, and beg the questions – “Did the man not go give a hard look at standing examples?” & “How is this still here?”

Two issues here - Chord Lams are for reason typically spaced apart - And a simple bolted Half Lap is no kind of Tension Splice - All of those found here show this kind of failure and loss of geometry

Two issues here – Chord Lams are for reason typically spaced apart – And a simple bolted Half Lap is no kind of Tension Splice – All of those found here show this kind of failure and loss of geometry

That itself is a mystery of sorts. It is certainly not that it has enjoyed exceptional care and maintenance over the long term. It appears that part of this story is that the small mills, and the towns they supported on its either end, struggled, And as is common to other areas where circumstance and money left…

This Drop is shorter than is the typical standard, one of many clues which suggest a lack of familiarity with Bridgewrighting among those who framed the bridge – This lack of “end distance” was likely directly resultant in this shear failure

Without a booming economy driving “improvement” and change, time’s earlier stamp went untouched. Though seemingly less than desirable, such circumstance has left us much which would have otherwise been lost. Some of times most well preserved towns, pockets and places, as well as houses and barns, ironically stand as they do today for the lack of any money to update them. Thankfully here, the traffic count and the need, somehow also failed to demand replacement.

This short grain issue was caused by a Mortise cut too short - This section removed to compensate held an easily predictable outcome

This short grain issue was caused by a Mortise cut too short – This V-like section removed to compensate held an easily predictable outcome

When the need to be able to carry fire apparatus and school buses did demand a change, an usually high clearance height for its time saw it rejiggered to increase load capacity, and again, The Jericho was not replaced.

Those of us who both build, and work to preserve the work of those we follow, often see this as a promise shown to us in the workmanship in the structures we work to sustain and maintain. It being understood that the better something is built the longer it is likely to last.

And sometimes (though only sometimes) we find proof positive that what time has carried for us into our time, is as much about happenstance as it might be about anything else.


Over the Fence

I missed my last time touchstone, my volitional calendar driven deadline – June 30th was for me a travel day, a return from an all too brief trip home, back to the current project bridge. It began as such days always do, then it somehow went beyond sideways. My phone went missing, and the airline employee who made it gone, looked me in the eye and told me she’d not seen it. In the ten minutes that passed before I realized just what had unfolded, that someone without the typical faceless anonymity of an average random thief of opportunity, had willingly thrown my life into upheaval and turmoil. She and it were ten minutes away and forever gone.

And though my June entry was fully planned and outlined, it was not yet put to paper – My distraction, hugely fueled by anger, meant one more thing went missing that day. Without any ability to know what they had taken, this thief had also stolen my muse…

So, my thought now, is to counter this thing of how horrible human beings can be to one another, with a story of just how wonderfully it is we can, almost without knowing it, touch the lives of those around us.

I would not be involved in the project I am right now, nor would I be writing about the subject of Bridgewrighting but for a simple act of kindness extended my way some twenty plus years ago now. I was newly returned to my home state after two years riding out that last recession in a Timber Shop in the Sunbelt, this followed by a nine month stint as a Journeyman Timberframer working on two historic replications in two far flung states. With a return to our homeplace, the family and I settled into our new home, I went back to work with an old friend. Weeks later the news of the day suggested I attend the launching a newly replicated Town Truss bridge which had been lost to arson just the year prior.

Thousands were in attendance, there to watch the out of the ordinary unfold – A nearly fully assembled traditionally built wooden through truss bridge being slowly rolled into place by multi-part Block & Tackle drawn up by rotating teams (this a double meaning) of Oxen being twitched around a capstan.

I was awash in a small sea of humanity, yet somehow. an acquaintance I knew from attending trade group presentations he had given, and with his having served as design engineer for a replication project I had been tied to in his adopted state of North Carolina some five months before, recognized me in that sea of faces. David Fischetti (< Click the underlined text for a deeper sense of the the man) called me over to the fence separating the crowd from the work area and suggested I needed to meet the Bridgewright heading up the efforts, he also suggested I hop the fence and follow him. David introduced me to Arnold, saying we ought to know one another, after very brief “Good to meet ‘cha“ pleasantries, I was asked if my tools were in my truck, and it was suggested if I had a mind to help “There’s a fella down under the bridge that could use a hand with some Timbah frame’n” – I spent the next two days working cooperatively, scribing, cutting and emplacing Lower Lateral Braces into a slowly rolling bridge. The fella I was tasked with working with that day is someone I have been working with on and off ever since. It so happens I’m helping Tim on the current project…

Years later, though we had crossed paths in the ensuing years, I took a few moments after attending another of David’s talks on Preservation engineering given to the Timber community, when I had the presence of mind to bring up his introductions that day, and to thank him for unintentionally changing my life, and to drive home to him, how his simple wave over, had for me, done so much.

Though this his choice had done, and that day sits so high in my mind as life altering, for Dave it held barely a glimmer of recollection.

With stories swapped with others who knew him well, and far better than I, I am convinced it was not just that busy weekends activities and the years that had passed, that shaped our differing recollections of the day. It was just that such a wave over and a hand up, were everyday for David. This was simply his nature.

Though such displays of gratitude are not entirely like me, I am forever glad I did reach out in return, as David was prematurely taken from us just a short few years later.

Photo credit for this image of the Corbin, the bridge where this story came to pass - Doug Kerr - Some rights reserved

Photo credit for this image of the Corbin, the bridge where this story came to pass – Doug Kerr – Some rights reserved

So, I ask this of you in remembrance – If you ever look over the fence, (be it physical, or implied and analogous) and recognize in someone on that other side, an earnest and deep interest in what it is you are doing…

Extend a hand, reach out, and invite them up and over, and be there.
Be there like David.


We Seemingly Need a Glossary

Distractions, and in my self imposed deadline week – Travel, and a new temp home wrapped around a new project…

Beyond the multitudes of expected newness’s, lay of the land, where is it I find what my everyday needs, and that ever present requisite that a real nights rest, for most of us, requires at least some small familiarity.

I somehow find myself again challenged by – Nomenclature, or rather the failure to use it, and the willy-nilly substitution of unfounded nonsense terminology. Despite having seen this time and time again, I will never get used to it.

As always, the drawings for the specified repairs are ripe with misnomers, guesses, and well, a little creativity?

I am a student of language, and accept creativity as part of our ongoing process in our ever evolving tongue. I do however refuse to accept “creativity” borne either of laziness, or far worse – Simple ignorance, this compounded in a needless refusal to open a book, click a mouse, or flick a finger at a touch screen.

So, though I did not see it coming – This entry will be an ongoing work in-process – A Glossary of Terms, specific to wooden through trusses / covered bridges. A quick click and a glance at the almost bottomless interwebs, suggests there is somehow no such fully fleshed out beast to be bridled?

Every last slice of the layers that are our over-lapping sub-cultures in our very human existence are rightfully ripe with geek-speak. This sub-culture, though nearly lost, has a history and an accepted sense of what word, means what.

If you hold an interest in any of that, do click back, or in the future do a simple web-search for “wooden bridge truss / covered bridge glossary”

This entry will in the coming weeks and months, morph into that, a comprehensive glossary of wooden bridge specific jargon and bridgewrighting terminology.

The current project - And the naked wooden through truss, laid bare for the effort  - What parts is pieces and what names do they go by?

The current project – And the naked wooden through truss, temporarily laid bare (Un-Housed) for the effort – What parts is pieces and what names do they go by?