This ramble finds us returning to our very beginnings. Those of this weblog and our ongoing series on New Hampshire’s historic connections to wooden bridges, and a first entry mention of Mssr. Timothy Palmer’s Piscataqua “Great Arch” near Portsmouth New Hampshire. We will also look into another of Palmer’s still noteworthy and known and to history spans, The Schuylkill Permanant Bridge at Philadelphia. Itself a beginning, widely acknowledged to have been the first of North America’s bridges to be “Covered” – And the man’s own words will tell us why.
Though not his first large and long bridge building effort, The Great Arch at 244′ was Timothy’s longest ever span. Seen as a marvel of its time, it brought worldwide attention, and great renown to its builder. And was arguably directly attributable to this Newburyport Massachusetts resident native being offered bridge framing contracts as far afield as the Potomac at Georgetown.
Descriptions such as this, were quite commonly shared by then travelers to the new America, and were part of the renown brought to the builder of “The Great Arch”
Palmer was granted a patent in 1797 which in all probability would have held details of the framing of his Great Arch, had all record not been lost in the Patent office fire of 1836. ( see Dec ’11 archived entry Long Lost ) We do know it featured multiple lamination Chords composed of 16 X 18 X 50 Arch Ribs hewn following a natural curve in logs chosen and harvested specifically for this purpose, and that the Arch rose twenty seven feet at mid-span.
The Permanent Bridge, built a decade later. Was like The Great Arch, built by a for profit company formed for this purpose and funded by the sale of stock. In part to maximize fully any potential return on this investment for the duration of toll taking period allowed by the city’s charter, until that charter required it be turned over to serve as a free bridge. And additionally to allow it to continue to carry any and all traffic types for that duration, meaning Drover led stock taken on the hoof to market, and the heavier Teamster type loads of freight which demanded the larger tolls – The Schuylkill Permanent Bridge Company President Judge Richard Peters, saw fit to suggest the company board in and roof over their bridge.
Palmer, their chosen bridgewright, had long been a proponent of such enclosure to protect his work from the elements and extend its service life, and explained in great detail the simple reasons why in a letter to one of their agents:
Opened to traffic on New Year’s Day 1805, it would though ultimately be removed and replaced in 1850 with a truss without any arch following rises in its multiple spans, these being unsuitable to also carry the rail traffic its replacement was expanded to accommodate. Palmer’s Permanent Bridge exceeded his conservative suggestion that boarding in his through trusses might add as much as thirty or forty years to a wooden trusses service life.
And time has proven that such trusses, with a properly maintained enclosure have an exceedingly long service life. Surviving examples in both New Hampshire and Pennsylvania are yet carrying vehicular traffic, now well beyond their 175th year.
Palmer’s final bridge, built the following year, spanned the Delaware connecting Easton Pennsylvania and Philipsburg New Jersey. It featured an improvement, of a level floor through his Trussed Arches. It would continue to carry traffic until its removal in 1895. An end and a replacement, which like that of the Permanent Bridge was more about traffic type and volume, than a service life which had reached its end.