Tag Archives: Historic Preservation

Numbers as Great as They Now are Few

A different shake of the box this go, no external wonder over maddening happenstance. This time a glimpse of history and not from my typical perspective, this go we will look at what was, simply because it is so little looked at, and with that somewhat under-realized.

We are about to look at wooden Pony Truss bridges and in the doing, we will explore what was with photographs in numbers greater than is typical of our explorations. Though unlike the allusion of our chosen title, which speaks to how common Wooden Ponies once were and how remarkably those numbers have dwindled, dwindled to a point just short of totality, from untold hundreds if not thousands, to a count which depending on how you categorize the type, which can arguably be seen as countable on one hand.

Old Russell Hill

The Old Russell Bridge of Wilton New Hampshire is sometimes also known as The Livermore

Wingwall

The Russell Hill carried traffic until recent years and is in all likelihood this was the last Boxed Pony Truss Bridge to have done so

Pilaster

The Russell Hill is a Town Lattice Truss – The Pilaster (and the concrete pad which supports them) seen lower right was added to take up load inboard of the compromised Chord ends to keep the bridge in service – The decayed Chords are likely a result of unchecked leaf litter building up between the Back walls and the Truss ends which slowly decomposed into a soil like matter holding moisture borne of rainfall against the Chord lamanie for weeks and months until they likewise decomposed – This an entirly preventable set of circumstance

Pony Trusses were a common solution for short span situations bridging waterways of twenty to sixty feet. In essence a Pony is a Truss short in stature, of a height less than that which is typical of a “Through Truss” – Perhaps the most common approach to weatherproofing Ponies was to “Box” them in, to simply board in both sides of both trusses and to put a little Roof-ette over each of them individually.

This is almost certainly why the landscape is now almost devoid of “Boxed Ponies” – This approach left the Flooring and the Floor Beams exposed to the ravages of the sun and rain and the oxidation and decay such exposure encourages. My educated guess is that long ago replacements were about the need for the regular maintenance wood exposed to the elements requires. With the maintenance regime such exposure demands, Boxed Ponies were in time replaced with Creosoted timber stringer and bent piling bridges and concrete box culverts.

Moose Brook Conwill

The B&M built Moose Brook Bridge seen here while still in service nineteen years prior to its loss to arson – This photo was taken by Joseph D. Conwill – Joseph over a period of decades has visited every wooden bridge in North America, many such as The Moose Brook no longer exist

New Hampshire through a collection of happenstance, climate, Yankee thrift, and the sheer numbers in late examples built by the Boston & Maine Railroad stands as home to most of the Boxed Ponies still standing. One of these was lost to arson in 2004, several years later I helped Barns & Bridges of New England, The National Society for the Preservation of Covered Bridges and NPS-HAER in the replication of its trusses with salvaged iron Rods and Angle Blocks from the original. These were used as full-scale models at Case Western Reserve University in an engineering study and have now returned to NH and are in search of a future home.

Moose_Brook_Axonometric_Cutaway

An As-Built drawing of The Moose Brook created by the Historic American Engineering Record – Seen here as a courtesy of NPS-HEAR and the Library of Congress

Rod Clearance Cuts

10 X 16 X 48 Chord Lams laid down on edge to allow for the cutting of clearance cuts for the Moose Brooks massive Truss Rods

Ready for Placement

Angle Block Abutments and a bird’s eye view of the Truss Rod clearance Cuts – Though a Howe truss differs from most other types in that Iron parts join those of wood this is still necessarily done with the high levels of tolerance required for Truss Framing to sustain intended geometry under the massive loads they are designed to bear

This video, though a bit grainy, does drive home the tolerance of fit strived for in wooden bridge framing. Here, Tim Andrews of Barns & Bridges of New England guides a Truss Terminus Angle Block into place as I lower it with hydraulic assistance

Reynolds

The Reynolds Covered Bridge stood on Blue Ball Road in Cecil County Maryland until 1949 – This Queen Post Pony was built by Joseph G. Johnson the same year he built the Gilpin’s Falls – This Image is seen here as a courtesy of Jim Smedley and mdcoveredbridges.com

Not all Ponies were Boxed, sometimes the choice was to protect the Trusses from the weather by adding a “House” as opposed to Boxing the Trusses independently, whether this choice was made to provide protection to the Floor Beams and the flooring they carried or if this was seen as money better spent, and a more affordable alternative over the service life of a bridge is something the record has yet to suggest.

The Colvin

This image of the Colvin Covered Bridge of Schellsburg Pennsylvania is seen here as a courtesy of Carolyn Williams – I find The Colvin a particularly clever and visually appealing MKP Pony and should you find yourself in need of a short span bridge I’d love to build you a copy

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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.


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?

 

000_0017

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.


Heritage Does Matter

Heritage Matters is a favored catch-phrase of mine, perhaps familiar to many of you as being the chosen name of newsletters and magazines published by those in the preservation / conservation community seemingly the whole world over.

I’m choosing to cite this phrase in this months entry in that I am penning it as a response to a number of recent news “stories” – stealth missions really, thinly veiled opinion pieces questioning the use of public monies to fund Covered Bridge preservation. The piece that touched a nerve, visited a single bypassed bridge, and suggests spending dime one to maintain such is wholly unreasonable, then goes on to intimate that funding maintenance on any example is money poorly spent.

I would ask those suggesting zero maintenance what alternative is it they see or might suggest. The funding of immediate demolition? The gating of Portals and simply letting time and neglect take the bridge to the river, someday accepting the inevitable expense of in stream cleanup and removal?

These are the only alternatives – Both are as silly as zero maintenance, and I would contend the cost of either would exceed the cost of decade upon decade of maintenance.

Postponing simple maintenance, is the unspoken of multiplier that drives up the cost of bridge rehabilitation’s. Timber does not simply go bad – Unchecked leaks in roofing or siding, and the buildup of dirt and leaf-litter, these all too easily preventable and correctable issues, are the causal factor in most all problems requiring any more than simple maintenance.

Putting aside that heritage tourism inarguably though indirectly offsets the cost of simple maintenance, (though perhaps not the costs of neglect) lets talk about heritage…

Unwittingly, even to those who care not one iota about history or historic preservation, Built Heritage still matters. In that this is where our sense of selves and place come from. The barns and historic homes we pass each day are our sense of place.

The Brownstones of Boston, Brooklyn and Harlem, the Victorian rowhouses of the Haight-Asbury, the Triple-Deckers of Mattapan, Manchester and Pawtucket, the Log Crib Barns of Appalachia, the Forebay Barns of Pennsylvania and beyond, all provide our sense of region and place.

This sense of place is also carried by the Howe Truss bridges of Oregon and the place-bound iconic Kennedy Portals of central Indiana – These things are all part of the landscapes which tell us who both we, and our Grandparents are. These things are who we are.

Forsythe Covered Bridge, Orange Township Indiana - Photo credit  James W. Rosenthal - Use courtesy of The Library of Congress, Prints and Photograph Division HAER: IN-106-2.

Forsythe Covered Bridge, Orange Township Indiana, Built by Emmett L. Kennedy & Sons
Photo credit James W. Rosenthal – Use courtesy of The Library of Congress, Prints and Photograph Division HAER: IN-106-2.

Transportation Heritage like all Built Heritage is part of this little thought of, almost subconscious sense of who we are. With any and every example of our built heritage forever removed from our landscape, part of who we are is also lost.

Our sense of place is now being endlessly eroded and homogenized, as it is re-placed with strip-malls, chain restaurants and tract-mansions.

Heritage lost, is the loss of who and what we are, both as a culture and a people.

Why would we want to intentionally fail to maintain any of it?


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.


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.


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


119′ Clamps

Recently a cyber acquaintance visited the Gilpin’s Falls, a bridge I, as part of a team of three, helped restore for many long months back in ’09. His photographer’s eye for detail saw him notice and ask after the now unusual way the floor of this bridge is assembled…

It’s a good story, and I thought I’d elaborate here, and use it as a catalyst to finally kick this blogging thing off and up a notch.

The floor as constructed, exists because knowledgeable people found historic evidence, made a case and lobbied for a construction detail to be returned to the bridge. It also helped that this evidence did not fall on deaf ears.

The floor system on the Gilpin’s had been almost wholly replaced in the 20’s, the last decade the bridge carried traffic. This in a failed attempt to increase its load carrying capacity, all the Floor Beams but one, all the Sleepers, (longitudinal joists which run from Floor Beam to Floor Beam) and all the Flooring, had been switched out from softwood to mixed species hardwood. The Flooring had also been installed on a slight bias, (though so slight as to not lend any triangulation and bracing effect) and this proved to have been done simply to avoid any need to cut the material to length, it was simply laid down in the raw rough slightly random lengths provided by the sawmill.

Occasionally things fall together as they should, and as we disassembled the floor system, it became obvious that the hardwood replacements had suffered massive infestations of Powderpost Beetles and would again require replacement, this was fortuitous in that the huge increase in weight and dead load they introduced had been directly responsible for much of the distortions to the bridges framing.

As we dismantled the Floor we found long multiple panel / bay sleepers, with longitudinal rebates and unused bolt holes. The use of these “rabbits” had been long abandoned, but we found their intended original use obvious, having read about such systems, most notably in the very descriptive hand written proposal documents of Indiana bridgewright J.J. Daniels and in the writings of Col. Long.

They are part of a simple but ingenious flooring clamping system, which obviously once saw use over a wide geographic area. Its advantages are based in a simple understanding of the materials being used, the intent being both to allow the clamp to be loosened after the flooring seasons and shrinks, rows of flooring to be tightened up, and gaps filled by adding additional pieces. This system also avoids the damage and reduction to service life in Sleepers, which comes with the repeated spiking down of flooring as wear demands its repeated replacement.

We returned these pieces to their intended use, and it is possible, if not probable, that the Gilpin’s Falls Covered Bridge is the only existing example of this system in use today.

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