America's Covered Bridges. Ronald G. Knapp

own eyes, we must ask where were they? Possibly he had seen the drawing in The Columbian Magazine of January 1787. Perhaps he had heard of covered bridges in Europe and thought they were in the United States. However authoritative his statement may sound, there is no corroborating evidence. Thus, Palmer’s 1805 Permanent Bridge retains the title of “first covered bridge” until there is hard evidence showing otherwise.

      This milestone, however, important as it is, privileges the least significant of Palmer’s innovations. Everything else about this bridge and the ones preceding it built by Palmer and the two Spoffords demonstrate the real progress made in American bridge design: the development of deep-water pier construction, the rapid evolution of timber bridge trusses, and the ability to construct massive spans of exceptional length and strength. After this, successive builders created ever more innovations in truss design, and America’s first professional engineers developed the science of stress analysis, making bridges ever more rational and efficient. Their story will be told in Chapter 2.

      More Remarkable Bridges: Theodore Burr and Lewis Wernwag

      After knowledge of Palmer’s Permanent Bridge spread, the idea of covering a wooden truss bridge to protect it from the weather was no longer considered odd or controversial. Covered bridges soon became the norm and continued to be so until the building of timber truss bridges was phased out during the late nineteenth and early twentieth centuries. The essence of covered bridges, then, is what the roofs and siding protect—trusses and other construction features. This vast subject will be treated systematically in Chapter 2.

      Timothy Palmer, although having achieved near perfection in Philadelphia, built at least one more bridge before his death in 1821, the three-span 490-foot bridge over the Delaware between Easton, Pennsylvania, and Phillipsburg, New Jersey. Theodore Cooper visited this bridge in the 1880s and reported: “This bridge, after eighty-four years’ service, is still in use and about five-sixths of the original timber is in good condition. It has always been covered in from the weather” (1889: 8). His Plate V includes a drawing of the truss, demonstrating that it was a virtual copy of the Permanent Bridge. Photos show that he even copied the painted-on stone arch bridge effect for the lower portion along with a similar series of windows above (Allen, 1959: 52). This was possibly America’s second documented covered bridge.

      Overlapping Palmer’s time, however, was the next up-and-coming bridge builder, Theodore Burr (1771–1822), whose short life included some of the most ambitious and daring bridge projects ever attempted in the United States. Though he was born in Torringford, Connecticut, Burr’s major bridges spanned rivers in New York, Pennsylvania, and Maryland. The son of a millwright, he moved to Oxford, New York, in 1792 to continue his father’s craft. Thus, his earliest work included a local grist mill, a dam, and an open bridge over the Chenango River in Oxford, a small village located midway between Binghamton and Utica. Successful as a builder, between 1809 and 1811 he built for himself a large Federal-style house in Oxford which, years later and with two added wings, became the Oxford Memorial Library and is now the home of the Theodore Burr Covered Bridge Archive. Burr’s many bridge building activities, however, necessarily kept him from enjoying his grand home.

      Palmer’s last bridge, connecting Easton, Pennsylvania, to Phillipsburg, New Jersey, across the Delaware River was 490 feet long in three spans, nearly identical to his Permanent Bridge. Built before his death in 1821 and covered from the beginning, the bridge was finally torn down early in the twentieth century. (NSPCB Archives, R. S. Allen Collection)

      Fortunately, a number of original letters written in Burr’s hand survive, giving us a first-hand impression of the man. Hubertis M. Cummings’ authoritative article published in 1956 in Pennsylvania History offers the best summary of his work. Since Burr moved with his young bride, Asenath Cook, to Oxford just as Palmer was beginning to build innovative bridges in Massachusetts, it is doubtful that Burr ever saw them. With skills in mill construction but little bridge experience, Burr nonetheless boldly entered the bridge building business. Between his 1800 debut in building the bridge in Oxford and 1808, he constructed at least seven more bridges, none known to have been covered at the time of construction. The first of these was a 400-foot “drawbridge” over Catskill Creek at Catskill in 1802 followed by a 330-foot bridge at Canajoharie over the Mohawk River. Of these we know little, but clearly Burr’s early bridges exhibited an experimental spirit. Where Palmer created and perfected a specific pattern combining truss and arch, Burr tried out completely original structures in his Mohawk and Trenton bridges as well as used a more conventional truss-arch pattern in other bridges, the latter becoming the foundation of what we now know as the “Burr truss.”

      Because of its longevity, we know much about the Lansingburgh-Waterford Union Bridge in New York State, built in 1804. With a length of 800 feet, it was the first bridge across the Hudson River. Consisting of four two-lane spans, each a different length ranging between 154 and 180 feet, its level roadway passed through triple trusses of X panels and massive arches, each of the latter having eight layers of wood bolted together. Had Burr covered it initially, he might have beaten Palmer for the distinction of “first covered bridge,” but his massive arches were left exposed until 1814. Because the bridge lasted until it burned in 1909, there are numerous photos. Compared to others he built, this was fairly “conventional.”

      Far more experimental was Burr’s next project, the five-span bridge over the Delaware at Trenton, New Jersey, with two spans measuring 203 feet each, one at 198 feet, one at 186 feet, and the last at 161 feet, these said to be “clear” spans. Thus, the bridge’s total length was well over 1,000 feet. Cooper, who also visited this long-lasting bridge, originally built between 1804 and 1806, described its construction: “Each span had five arched ribs, formed of white pine plank, from thirty-five to fifty feet in length and 4 inches thick, repeated one over the other, breaking joints, until they formed a depth of 32 inches. . . . The roadway was suspended from the arch ribs by vertical chains. The arch was counter-braced by diagonal braces, formed of two sticks 6 x 10 inches spiked to the lower chord and secured to the arch above by iron straps” (1889: 8–9).

      Although the bridge lasted until 1875 when it was replaced by one made of iron, it had undergone various renovations in 1832, 1848 (to carry trains), and 1869. Cooper includes a clear drawing of the structure, including the flared ribs out 50 feet from the abutments and piers designed to provide bracing against the wind. Never covered in the conventional sense, Burr’s successful experiment had a partial roof over the top that followed the contours of the arches.

      Bold to the point of brazen, Theodore Burr’s 1,000-foot crossing of the Delaware between Trenton, New Jersey, and Morrisville, Pennsylvania, was unprecedented in design and only partially covered. (NSPCB Archives, R. S. Allen Collection)

      Burr and Palmer were contemporaries, but Burr succeeded in building bridges with level roadways when Palmer’s were arched. The Lansingburgh-Waterford Union Bridge over the Hudson used Burr’s usual design, having a panel truss with both braces and counterbraces, along with laminated arches. (NSPCB Archives, R. S. Allen Collection)

      Carrying both carriages and light rail, Burr’s Lansingburgh-Waterford Union Bridge crossed the Hudson River in four spans of varying length, totaling 800 feet. Built open in 1804, it was not covered until 1814 but lasted until 1909 when it burned. (NSPCB Archives, R. S. Allen Collection)

      Burr’s Delaware River crossing, connecting Morrisville, Pennsylvania, to Trenton, New Jersey, was one of the most noted bridges of its time, 1806–75. (NSPCB Archives, R. S. Allen Collection)