Theodore Burr Died Broke. His Bridges Are Still Standing.
Theodore Burr Died Broke. His Bridges Are Still Standing.
Theodore Burr was born on August 16, 1771, in Torringford, Connecticut — 255 years ago today. He died fifty-one years later in Middletown, Pennsylvania, apparently without money, without an obituary, and without a marked grave. In between, he figured out how to hold up a wooden bridge, and more than half the covered bridges still standing in Pennsylvania use his idea.
Baumgardener's Covered Bridge in Lancaster County, one of hundreds of Burr-truss spans across Pennsylvania. Photo via Wikimedia Commons.
Two ideas, glued together
Before Burr, an American bridge builder had two options and both had ceilings. A timber truss — the multiple kingpost, essentially a row of triangles — was stiff but ran out of span somewhere around a hundred feet. A timber arch could reach farther but flexed alarmingly when a loaded wagon moved across it, because the load never sits evenly on both halves.
Burr's answer, worked out around 1804 and patented in April 1817 as US Patent No. 2769, was to stop choosing. He sandwiched a multiple kingpost truss between two long timber arches that landed directly on the stone abutments. The arch handles the weight; the truss keeps the whole assembly from wobbling. Or the truss handles the weight and the arch provides stability — engineers have been arguing about which member is really doing the work for two centuries, and modern computer modeling has come down on the side of the truss. The bridges themselves seem unbothered by the dispute.
The arch, visible from inside White Rock Forge Covered Bridge — laminated timber curving up past the crossed posts of the kingpost truss. Photo via Wikimedia Commons.
What that bought him was reach. Burr spans run from about 33 feet to 222 feet, and that upper number is roughly ten percent longer than what a Howe truss — the iron-rodded design that eventually replaced it — could manage. For a country that had a lot of rivers, very little cash, and enormous quantities of standing timber, this was the right invention at the right moment.
The Susquehanna years
Burr came to Oxford, New York, in 1792 and started out unremarkably: a grist mill in 1794, a dam to run it, then a plain stringer bridge over the Chenango River in 1800. By 1804 he was throwing the first substantial bridge across the Hudson at Waterford, which stood until fire took it in 1909.
Not everything worked. His 997-foot span at Schenectady in 1808 was a suspension bridge held up by wooden cables, and it began to sag almost immediately; four additional piers had to be shoved underneath it. Burr was a builder first and a theorist second, and occasionally the river reminded him of the difference.
The Susquehanna is where he made his name. Between 1811 and 1818 he designed, built, or supervised crossings at Nescopeck Falls near Berwick, at Columbia, at Harrisburg, at Northumberland, and finally the 4,170-foot monster at Port Deposit, Maryland. For a stretch there, essentially every bridge over the Susquehanna from Binghamton to the Chesapeake was his.
The one worth remembering is McCall's Ferry. In 1815 Burr threw a single 360-foot arch across one of the river's narrowest and meanest gorges — still the longest wooden span ever built, more than two centuries later. It lasted three years. In March 1818 the river came up, ice jammed in the gorge, and the bridge left its abutments. One arch fetched up eight miles downstream near Peach Bottom. Another floated under the Rock Run bridge and grounded on the flats below Havre de Grace, roughly twenty miles from where Burr had put it.
What's left
Burr's own bridges are gone — fire, flood, ice, and the practical needs of the twentieth century took every one. His truss, though, outlived him by a wide margin, mostly because county road crews found it easy to build and hard to break. Pennsylvania's longest surviving covered bridge is a Burr: the 278-foot, double-span Academia Pomeroy over Tuscarora Creek in Juniata County, put up in 1902 by James N. Groninger — eighty years after Burr's death, and eighty-five after he filed the patent. It's been owned by the Juniata County Historical Society since 1962.
Indiana kept even more of them. Of the state's 92 remaining covered bridges, 53 are Burr trusses, with a heavy concentration in Parke County. Cross one and look up: that long curve of laminated timber running past your shoulder is an 1804 idea, still working.
Photo via Wikimedia Commons.
Burr died in 1822 while supervising yet another bridge, at Middletown. He was, by all accounts, a terrible manager of money and a superb manager of timber. Nobody wrote him up in the papers. There's a covered bridge society in Pennsylvania named for him now, which is probably the memorial he'd have picked anyway.