Of Curves and Chords

In casting a wide net to both pull together a non-blog bio piece on Timothy Palmer, and in searching deeper for more information on the Trussed Arch Trusses a type commonly associated with him, (not to be confused with the Burr Arch images to be found below) I came across John Trautwine’s 1834 description of the construction of a ‘987 bridge (Then the longest Railroad Bridge in the world, built just one year prior) which came to be known as The Great American Viaduct – From The Journal of the Franklin Institute of the State of Pennsylvania Vol. XIV No.2 August 1834 – A piece titled – Description of the Viaduct near Peters’ Island – and thought excerpts worthy of a share here.

The whole of Trautwine’s description is ripe with seldom recorded details, from description of the coffer dams built to construct the piers, (and the steam engine used to pump them out) to the trestles emplaced to be used as falseworks on which to re/assemble the Trusses as they were erected over the Schuylkill. To how this Double Barrel was intended for one lane to serve rail traffic and one to serve foot and wagon traffic. (Several Philly area early Railroad bridges were two lane constructions for this purpose)

The following excerpt is intriguing in that it describes and pays homage to Palmer’s nearby Permanent Bridge which still stood at the time this Description was put to paper –

Always of interest to me is the period nomenclature (in this instance a wealth of it) found in this kind of first person source material – Here Joggle is again found to be the term of choice for the opposed swellings often milled into Posts in MKP variants to receive the Braces – It being to my mind logical to use common construction era terminology in our time also.

A rare treasure trove for wooden bridge geeks (this one in particular) are deep description of construction details little found elsewhere, detailing so descriptive the author begs pardon for the tedium borne by the reader…

I for one, am most thankful to John for these very details little shared, and this glimpse through time into his world, a world almost lost to us but for yet standing examples, and in words of description such as these, from the very minds of those who have left us our wooden transportation heritage.

We have yet to discover when this bridge was lost to time.

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About Will Truax

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

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