Tag Archives: Irene

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.

Van_Gogh_-_Trauernder_alter_Mann.jpeg

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.

blenheim-mid-span

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.

blenheim-lower_arch

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.

blenheim-midspan_kiss

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.


What Was Lost…

The entry here on the the Bridgewright Weblog which has seen more readership than any other, (and is still clicked in on with regularity) is now some thirteen months old. A piece titled Lost to Evermore, written in part in reaction to the devastation wrought by Irene. Some of which, as I put pen to paper in those first few days after the storm, I had already seen firsthand. Some, in the hard-hit Schoharie Valley of New York was at that point, less than fully known, to myself nor most anyone from outside the immediate area. Lines of communication were then down, and travel in and out of the valley was so hindered that little information about the level of damage had yet reached the wider world. What was known was that The Blenheim had been washed from its abutments.

With less than little known about the level of damage done to the Bridge, and with this blog being Bridgewright-centric, (for the most part but not limited to, an exploration of the works and work of Bridgewrights – Builders of wooden bridges, both past & present) my piece was as much about the builder of the Blenheim, as it was about the bridge itself.

The Bridgewright Nichols Powers – Photo courtesy of Schoharie Historical Society

Information then available suggested the bridge was not only lost, but had been all but erased – Even weeks later, in a group of folks at a Regional Gathering of Timber Frame Carpenters many of whom knew and had spent time on, in and under The Blenheim, (It being to the North American Timberframing Community among the greatest of timber works to be seen, a built heritage pilgrimage of sorts somewhat akin to Chartres, the Parthenon or Pont du Gard) no one knew either what was lost or what might yet be found.

Many of us from outside the area assumed that the needs to replace and repair homes and businesses, to restore livelihoods and a sense of normalcy were the demands of the day for those directly affected by the floods. It was seen as perhaps not even reasonable to wonder after the post flood state of the Bridge.

Yet despite all this much to do, locals somehow made time for their Bridge. A recovery effort was organized, advantage was made of the seeming irony of a mild, almost snow free winter, and regular efforts in search and retrieval were made.

This gained a sense of urgency when the Blenheim’s National Historic Landmark Status was seen as in jeopardy, and it was suggested that any effort at rebuilding would have to include 51% of the original “fabric” to retain Landmark status. A lower than typical Spring Melt also cooperated with efforts towards recovery, and activity intensified as the weather warmed.

And more recently even as recovery efforts saw the transfer of sections both large and small to a common staging area, another setback. A FEMA determination that the The Blenheim, because it no longer carried vehicular traffic, is ineligible for funding. An appeal of this decision was recently heard, the finding and a final decision is yet to be determined.

Some of you may remember the shot of the Bottom Chord Scarf (Splice) I included in the Evermore piece. I no longer see the Bridge as lost, (If I ever did, the piece was about circumstance and reaction) or the situation as evermore. I do still see that magnificent Scarf, that startlingly beautiful and complex bit of cooperative workmanship, as being a yet unbroken connection still tying the Bridges past, to its future. I see this as area residents do – The need is to rebuild.

Preparations for rebuilding began, but will not end, with recovery and retrieval.

The following shots were taken on a recent non-related timberframe restoration trip into the area – Several of Powers chosen multiple abutment “Trait de Jupiter” (Bolt ‘O Lightning) Scarfs are seen here also…

The Bridled Tenons which control the Wedge where the Counter joins an Arch

Double Mortises and a Flatting cut perpendicular to the axis of the Counter Braces in an Arch section to receive a Counter and its Wedge

An Oaken Angle Block & a Cleat to receive a Set of Lower Lateral Braces and the Tie Rod which controlled them

The Blenheim materializing out of the mist on an early morning visit in the Autumn of ’07


Well Founded – Sticks and Stones and Service Life

Typically it is the sticks and bones of these wooden bridges which I concern myself with, not the stones which carry them. With how all important this founding is to the service life of the bridge it carries, in this entry we will depart from our typical discussion of the history of wooden bridges and the people who designed and built them, and turn to the stonework, and the soil on which that sits, and has carried them through time, into the present.

Dry laid Granite Abutment of the former Moose Brook RR Bridge - Note the Wingwall's invaders - Such trees should never be allowed to grow - In the streambed we find charred Bent Pilings, perhaps the falsework Moose Brook was assembled on

This is the branch of bridge engineering which has for me, tended to perk the least amount of interest. Talk of soil science and subsurface profiles and standard penetration tests tends to have my eyes glazing over. At the same time, having read a number of historical proposal documents with richly detailed descriptions of abutment construction, and with having more than once been present when such constructions were being rehabilitated, I’ve been able to see abutment stonework from perspectives not often available to us. With their bridges lifted or temporarily rolled out of place, and with partial excavation exposing inside faces of the stone. There is often more to such an assembly than might be imagined by looking at what can be seen from above ground. This is particularly true for Burr’s and other trusses with original Arches, something often unseen is there to take up the thrust imparted by those Arches.

Stonework, and an awareness of the power and effects of moving water, have almost always been part my understanding of how our world works. My childhood home stands quite literally, on the rim of a deep gorge, carved out over eons by a tributary of the Merrimack River, their confluence not a mile downstream. This seemingly gentle but ten foot wide picture book perfect example of a babbling brook, two hundred feet below the gorge’s rim, stood home to a long abandoned mill site. As seasons turned and flowed into passing years, I would mark each newly unfolding year with a post Spring Freshet exploration of what changes each annual melt swollen flood would bring to the gorge. This would begin with the mill site, constricted in flow by massive dry laid granite walls on either side of the brook, always annually exposing former mill parts, cogs and castings, long buried in the stream bed and unseen for generations, and might end with some massive course change in the brook itself and the falling of trees this would bring.

I was reminded of the stunning ferocity and sometimes almost subtle power of moving water on 29 August 2011 when I trekked tools and materials to Rockingham and its village of Saxton’s River to help with the emergency stabilization of Hall Covered Bridge. The ferocity of moving water was more than evident in the almost impossible to process level of damage which lined both the William’s and Saxton’s Rivers. Seemingly unending property damage, including the loss of homes and livelihoods, and an unfathomable amount of riverbank erosion and immeasurable course changes.

The subtle side of damage done came in the form of earth giving way below my feet. Outwardly normal looking ground just inside the upstream wingwall, which I had already traipsed a number of times schleping crib block and shim stock, suddenly gave way and I found myself feet dangling, hanging by my elbows in a sinkhole. Hours of high water, pressure, and torrent, hammering the normally high and dry wingwall, had forced flow through the dry laid stone, and washed the fines ( Sand / soil particles smaller than average in a mixture of particles varying in size ) out of the approach through the stemwall and out into the flood swollen river. This same abutment suffered heavy impact damage, multiple stones had been dislodged, and had peak water levels held for much longer it seems probable that enough soil would have washed out of the approach, that the stonework in the abutment would have become unstable, and that it and the bridge it carried would have been lost.

As near to lost as was possible

This for me exposed the Achilles Heel of dry laid abutments.

Don’t get me wrong, I’m in no way advocating anything like removal and replacement – Quite the contrary. Though many people think of concrete as a forever material, it is not. Were we using the same Roman recipe, (Opus caementicium) which they used in the construction of The Pantheon and Pont du Gard, yes, it might be a super service life material. The recipe we use begins to break down after ninety years and has a max service life of one hundred and twenty five years, beyond that it slowly degrades into a clay like crumbling muddle – ( perhaps this might better be a debate for a future entry ) Soft clods of degrading concrete was another form of wondersome unknown debris I would find in Watt’s Brook Gorge each Spring, some late and last incarnation of the long lost dam – To my mind a Wooden Bridge should be founded on abutments which have at least as long a service life as it does. And time has told us and does prove, that a properly maintained covered bridge could and should, (Sadly most suffer periods of poor maintenance, or worse, neglect) easily reach the two century mark.

The temporarily empty Backwall and Bridge Seat of the Bennett Bean Bridge

So what am I advocating? I’m not entirely sure, I do think, that as with all natural disasters, we learn much about how what we build is effected by them. Much about what needs changing, and much about what doesn’t. In this event we learned the loss of wooden bridges to flood waters, is not just about bridges floating out of place, up and off their abutments, but is as often about undermined abutments crumbling beneath them and quite literally pulling them into rivers.

I’m wondering out loud what we are doing with our lesson learned, and how many others noticed this phenomenon of sinkholes and the loss of fines and are studying what might be done about it?

I for one also wonder if perhaps part of the solution might be, not the typical pumping of high pressure grout in behind the stonework, ( with the potential for puddling and the destructive cycle of freeze thaw that possibly triggers ) but might lie in excavating behind upstream wingwalls and backwalls, ( at least in well laid up cut stone examples ) and retrofitting multiple layers of geotextiles and chipped rubber tires. A well draining buffer to keep the wash from reaching the Fines, to perhaps keep future floods from washing away more of our built heritage.


We Will

The simply staggering power of moving water has of course, been much on my mind lately. Too much really. With news of similar flooding devastation seemingly every few days, happening somewhere in the weeks since Irene’s visit to our patch of the planet. With travel into areas which suffered devastation, and research and planning for the probability that I will be involved in some of the rebuilding.

The Contoocook RR Bridge was twice tipped by floods in both ' 36 & ' 38, and both times righted and returned to service

It is in thinking about the rebuilding that I find some solace. And this not because it brings much needed work, but because history tells us the power of high water seems equaled and even excelled by the resilience of humankind to pick ourselves up and rebuild. And to learn in the doing.

The Hall, on the Saxton’s River in Bellow’s Falls, none so far from the lost Bartonsville, was itself, very nearly lost to Irene. With a large section of a dry-laid stone abutment washed away, and a set of Bolsters, (visibly displaced in this flooding footage) a support sub-structure, was very nearly punched out from beneath it at this same compromised corner.

We have been here before, like those we share similar experience with on these very same rivers and waterways.

Flood Scene, Wrack and Ruin Postcard

Just as they have done, again, we will rebuild.


Tropical Irony

A short blurb to bridge the gap.

There is more than a little irony to be found in this stunning reality…

In the just over six weeks time which has passed since The Timber Framers Guild’s Chester Bridge Project, two of the attendees who helped build a new wooden bridge in New Hampshire have happened upon and shared photographs of bridges lost to tropical storms in their home states.

Photo Katie Hill

Katherine “Katie” Hill, a Vermont structural engineer shared a photo of The Bower’s, a Tied Arch truss washed off its abutments in the aftermath of Irene.

Bruce Cowie a timberframer from Lancaster Pennsylvania shares a photo of the Siegrist’s Mill Bridge, a Burr Arch. This past weekend it was similarly washed out of place by Tropical Storm Lee.

Photo Bruce Cowie

There is hope that both will be returned to service.

Work on the "The House" continues and nears completion - Photo Darrell Quinn


Lost to Evermore

Those of you who occasionally click in on my twitter feed might recognize this image as its background. (click to enlarge) I’d meant to only someday post a blog entry about it. Someday, when I’d moved on from New Hampshire’s historic connection to wooden bridge building. The recent floods however have moved up someday.

Irene’s aftermath will long be memorable, perhaps in part for video caught as the Bartonsville slipped into the storm swollen Williams River. We still don’t know the full number of bridges lost or damaged, but we do know this image has several things in common with what is perhaps the greatest loss. There is no question that it was the largest lost, and arguably, (and silly, my dog’s better’n your dog, arguments were ongoing) among the very last of the giants, that being New York’s Old Blenheim.

The image is, for a number of reasons, one of my favorites. In part because it shows one of history’s giants. Many are not aware that such wooden giants existed, because they have long since been replaced, usually because they crossed at all too important, high traffic areas. As often, the piers they were built on were far more expensive and time consuming to construct than the bridge they carried, and they were wanted to carry a new span which could carry a higher volume of traffic.

This bridge circa 1866, stood just upstream from the confluence of the Susquehanna with the Chesapeake Bay. It was a fourteen span Howe – Thirteen of 250′ and a Draw Span of 175′, for a total length of 3,500′. It carried the rail traffic it was designed for until the 1906. And then was re-purposed in 1910 for vehicular use, and continued to serve another couple of decades until its removal sometime in the late 30’s. Its Piers still sit idle next to the yet operational Iron Railroad Bridge.

Another reason it’s a favorite, is because, though as photographic technology of the time demanded it is obviously posed, all the same, it captures the actual circumstance of that moment in time. Drawn from a photograph prior to the existence of affordable ways to print photographic images on newsprint, a common technique of the day. It shows us not only the Falsework still in place under the near span, and how that Falsework is designed to interact with the masonary in the piers, and how the seeming ornamentation in the masonry was designed with two-fold purpose to receive that Falsework. We also see crews at work, and various aspects of the bridge still under construction.

The Bottom Chords of the Double Barreled Blenheim

It also pictures two men at the images center. Though only a theory of mine, I don’t see it as much of a stretch. The one in the top hat is George A. Parker, engineer and designer of this bridge built for the Philadelphia, Wilmington and Baltimore Railroad. The man next to him with the cane, is undoubtedly his clerk of the works hand picked lead framer, and Master Bridgewright, Nichols Powers.

Parker and Powers, in building this span, on this stretch of the Susquehanna, which like the nearby Schuylkill, stood host to many of these early giant spans, quite literally joined the ranks of bridgewrighting’s giants. Palmer, Wernwag and Burr.

Nichols, eleven years earlier, also built the now lost Blenheim –

The Trait de Jupiter / Bolt 'o Lightning Bottom Chord Scarfs of Powers' Masterwork

Among other still existing bridges, he also built the Brown, near his home town of Clarendon Vermont. We are yet to hear how it fares in the aftermath of Irene.

Recent video imagery accompanied by particularly timely & poignant original music by Kevin Sullivan.