Tag Archives: Preservation Carpentry

Phenominal Impact

Massive truck damage is again the subject of current news stories – In this most recent incident the level of damage is beyond any level of understandability, so far beyond, that it is without exaggeration almost impossible to understand how the truck and the fool piloting it, made it to the other side.

Impact damage has long been an issue with Covered & wooden spans, with but the 20th Century exceptions of Oregon and New Brunswick and British Columbia, most such bridges were built before heavy trucks existed and clearances were standardized.

We have spoken to truck impact damage here on The Bridgewright Blog in prior entries, and of how the frequency of these impacts and the level of damage both seem to be on the rise in recent years. GPS systems are often assigned blame by the offending drivers, this most recent case included. I can’t help but wonder however if some of this is not perhaps due to the continuing disappearance of through trusses of any kind from the National landscape. Modest span through trusses of any type are virtually no more. In their stead we are left with concrete deck bridges. None of the wonder of trusswork to perhaps spark the imagination of future builders and engineers. Just the continuation of an unending ribbon of pavement, unending road – Road seemingly levitated over water, supported by what, few who find themselves crossing even glimpse into the rear-view for a second glance at but a blip in passing to wonder…

Thought need not be spent, road is road.

Clearance and load limit signs are found less and less frequently on that road.

All that and I still can’t understand this level of unthinking – I drive a diesel fired behemoth, large enough that it is a pain to park in most parking lots, high enough that clearance signs in parking garages and drive thru’s need be heeded, heavy enough that I am pushing it with three ton load limit signs.

So somebody pointing a Semi through the Portal of something so atypical as a covered wooden bridge, passing load limit and clearance signs in the doing, is impossible for me to understand.

In helping the Graton Assoc's with the restoration of The Blair One of the tasks I was assigned was replication of the the many missing & impact damaged Wind Braces

In helping the Graton Assoc’s with the restoration of The Blair for these last many months – One of the tasks I was assigned was replication of the many all too common story, impact damaged & impact missing Wind Braces

I’m wondering with this entry, what needs be done to avoid more of this phenomenon of impact as the future unfolds?


Commonly Un Common

The Square Rule is, as I suggested in the last entry, not just back on my current, but it is now my actual horizon. A part of my here is now everyday. As is this wondering as to why it was the people who chose to use it, this Square Rule, chose to do so.

It is a funny place to be in in more ways than one. As is the fact that I might gaze through a window few can share – I know what it is to wonder after the efficacy of which system to use for any given Timber Framed construction. To ask which system of Timber Layout, Scribe or Square Rule is the more, or even the most appropriate. This a window common to a few of my contemporaries. Though one last wide open for but a brief while, centuries ago now, when this rapid shift from the Scribe to the Square was yet underway.

And I think the perspective I view all this through, is far from common. To know traditional versions of both systems of layout is not common even among framers. To have a working sense of both historical framing of buildings, and those of bridges is maybe even more so. All this is a circumstance and a happenstance and a perspective, which was once commonly shared. The once sense of everyday of a common country carpenter, but now some of the little explored vagaries of a hyper niche carpenter. That said, I still see myself as a common country carpenter. Perhaps it is the every tree is a timber, commonality traditional timber framing has with the sawlogs we are often involved in “converting” – It is in this work, none so uncommon to choose timber in the woods and on the stump. Something we have done here as part of the Bernhard Barn restoration, the two Tulip stems which will serve as species in kind replacements of the one piece fifty foot hewn from the round Wall Plates still stand in their forest and yet touch the sky, and do not yet know that they will be part of the next chapter in the ongoing story that this Barn will continue to tell.

It often crosses my mind that this thing of being a Framer with an inter-discipline sense of things is an all too small club, one with a membership far far too short in numbers.

So, all that, and with the other high horizon focus, The Blenheim, seem to bring us back to where this blogging adventure began, with Long Trusses and The Square Rule and who might have taught who what, when it came to bridge framing, (see the May & June ’11 archives) now swings back and over into a parallel and perhaps as seemingly and an almost equally unanswerable exploration. Who was it who brought the roots of Square Rule to the table, and where was that place that they called home?

Semi parallel interwoven puzzles and a wonder after both, send us in search of clues to either, and we find yet another letter of shameless self promotion from the good Col Long –

All this information for but three pence, the price of a nail so small, most might think of it as a tack.

Do We Not Live in a Meritocracy?

Typically, I use this space to share historical lore I’ve turned up on our wooden bridges, or the people who designed and built them, occasionally I explore structural aspects of the various Truss types, and details of and perspectives on their framing. Today I’m going to break with those norms.

I’ve come to the conclusion that part of the value in having a Bully Pulpit, is that every so often one should pound it with their fist.

Every so often has arrived in the form of recent events – Yes, I’m going to do an opinion piece.

The replication, well the rebuilding ( The replacement as designed has dissimilar structural systems and engineered timber, so it will not technically fit the definition of a replication ) of a bridge lost to Irene was recently awarded. It was awarded to the low bidder. This in and of itself is not unusual, (hell, some jurisdictions require contracts be awarded to the low bidder, others require that low bids be tossed – You be the judge as to which dictum holds the greater logic ) What is unusual is that despite every other bidder having decent if not deep résumés, and the Request for Proposals citing a requisite three wooden bridge minimum work history, and the four lowest bids coming in at remarkably close price points, the contract was awarded to the local bidder, a concrete & steel bridge building company. With several newspaper articles (see the archives to the right – or click the following underlined text – “Yes he was local, his name was Sanford Granger” ) citing the reasoning being, simply, that they were local.

In the interest of full disclosure, I, along with other independents, was part of an assembled team aligned with one of these bidders. Some might see some of what I have to say, as so many sour grapes. In truth the effort I chose to align myself with, provided an alternate bid, one which those involved saw as important, but one which had the great potential to (and ultimately did) remove us from the running, both for additional design costs, and with leaving the dictates of the letting as proposed. This alternate a traditional design, one which, with a full understanding of wood as a building material, specified “Free of Heart Center” timber for the Lattice Plank and Chord Lams, and had lateral Bracing systems in keeping with Grangers’ design, and neither the Glu-Lam Floor Beams nor Penta (Pentachlorophenol) treatment of any of the materials. To my mind both are unnecessary expenses and absurdities. Penta treated wood is a danger to those cutting it, and so requires already worked timber to be shipped to distant treatment plants and back. It also is a redundancy, this is the purpose of the siding and roofing. And with human nature being what it is, treated framing is arguably a recipe for future neglect, treating only part of the framing insures that recipe leads to future expense, not future savings. And to Glu-Lams, to insist a bridge designed to carry modern day traffic requires the use of engineered timber, is to ignore reality, as the Railroad bridges described here in earlier entries demonstrate so well. But these are perhaps points to be made in some future discussion, back to the point at hand…

Though the news story’s make no mention of it, instead concentrating on the local aspect of why which concern was contracted. In all fairness, that local concrete & steel bridge company has pulled in both a bridgewrighting “consultant”, and a local (same town) CNC type Timberframer. The Bridgewright has his own reasoning for this alliance. ( I’m just glad someone will be there with some real sense of things ) The CNC Framer perhaps played an equal role in the decision to waive the three bridge requisite, and of who to contract. I for twofold reason don’t see their involvement as entirely logical or appropriate – Though I don’t have room here to flesh out all the reasons why in this entry, here’s the gist – And also what isn’t – This is not a blanket condemnation of an automated CNC computer driven approach to timberframing, 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 exist in this bridge, Ties as a for instance. Major sub-assemblies like the Trusses and Lateral Bracing systems were and are, for good reason, (camber) typically scribed, because there are subtle changes in even 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, this driven by the attitude of the Ties and their relationship to the changes in the inclination of camber along the spans length) and slight changes in length in successive panels with a trusses 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 (or worse such subtleties are lost to ignorance – I’ve never seen a set of drawings which acknowledged and quantified this camber driven phenomenon ) from a CNC type approach in bridge framing – Scribe Layout without question remains the most efficient approach to wooden bridge framing. (with such approach, changing lengths and angles needn’t be 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 was abandoned for most all other timber constructions.

The other slant on why I see no logic in automated timber part production, goes to my greater point – The perpetuation of my trade, and the passing on of knowledge to younger members of the Timberframing Community – Those who will practice Bridgewrighting in the future.

Bridgewrighting is a sub-specialty of Timberframing, with both skillsets and a knowledge base unique to this sub-specialty. Much of this having to do with the crush phenomenon common to bridge framing, and the planning for and control of crush. Much having to to with rigging and assembly, along with techniques having to do with the development of camber in new-builds and likewise, the return of same to bridges undergoing restoration. Such concepts shared are what makes a Timberframer a Bridgewright. I do not see such things being conveyed from practiced framer to initiate at an automated production shop, even if only separated by fifteen miles, any more than I see any return or transferable value to the betterment of this Trade in pounding home the importance of edge distance, to uninterested form carpenters as they endlessly drill Trunnel holes through clamped up Lattice Plank.

I can’t help but see this as an all too rare opportunity missed. An opportunity for those familiar with this little practiced form of construction, to pass on proven methodologies and techniques to others who will in turn go on to practice this sub-specialty in future projects.

So to the greater point. Despite a small but capable corp of trained and knowledgeable wooden bridge specialists, it is somehow in no way uncommon for such replication contracts, and those of the related type and far more common lettings, that of major rehabilitation’s to wooden bridges to be awarded to concrete and steel bridge companies, and unlike this instance, they don’t necessarily subcontract in anyone who has anything approaching expertise in the field. This has happened in some surprising jurisdictions just within the past year, such as Oregon, Indiana, Ohio and Pennsylvania.

These structures are too important and too complex to be entrusted to the uninitiated, the learning curve is far too steep.

Some jurisdictions already demand that such lettings only be contracted to those known to possess all the necessary knowledge and skills to execute them fittingly. They do this by requiring potential bidders to pre-qualify, and vetting their résumés, (or those of their primary subcontractor) prior to the submission of proposals and bid prices. Surprisingly, in none of the States in which such bridges exist in the greatest numbers, is this tact of a Request for Qualifications (RFQ’s) used across-the-board to limit those bidding these projects to those firms best capable of executing them.

If all this makes sense to you, particularly if you live in a state with numbers. Consider contacting your State and Federal reps, and insisting that such highly demanding public works projects, if funded with Federal grants, be it National Historic Covered Bridge Preservation Program (NHCBP) monies, or those from FEMA to repair or replace storm ravaged historic bridge infrastructure – By requiring that interested parties pre-qualify.

I for one, would like to believe we live in a meritocracy.

Gleanings from the Grit

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

Photo by and courtesty of C. Hanchey

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

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

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

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

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

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