Roofs Over Rivers

PrintPrintEmailEmail

Palmer selected his long timbers—sometimes naturally curved—and floated them downstream directly to his bridge sites. He put up three spans over the Merrimack River in Massachusetts, one over the Great Bay of the Piscataqua in New Hampshire, and then went on to conquer the Delaware at Easton, Pennsylvania, the Potomac at Georgetown, Maryland, and the Schuylkill at Philadelphia.

This last was a showcase for Palmer. The merchants of the city had at last been able to raise enough money to finance the long-wanted bridge, and they spared no expense to make it the pride of Philadelphia. The fresh paint on its lower structure was even sprinkled with stone dust to give the appearance of masonry. Since he wished his timber trusswork to be prominent, Timothy Palmer took a dim view of this at first, but when it was done—at the instigation of Judge Richard Peters—he graciously allowed that perhaps the bridge might last “thirty or forty” years as a result of the extra protection from the weather. (Actually, it lasted forty-five.) Finished in 1805, it was dubbed the “Permanent Bridge”; its arched roadway stretched across the Schuylkill in three spans for a total length of 550 feet. It was the first known covered bridge in America.

In 1812, another bridgebuilder got his start at Philadelphia. He was Lewis Wernwag, a German immigrant and designer extraordinary. At Fairmount he planned and erected a monstrous bridge across the Schuylkill with a single span of 340 feet, far and away a record for that day. As it neared completion, reports began to circulate that it would fall as soon as the scaffolding was removed. Soon the rumors were rife, and on the morning of the day set for the removal of the falsework, thousands jammed the banks of the river to see the expected collapse.

The bridge-company managers were naturally worried, and assembled on the porch of Sheridan’s Tavern nearby. when Wernwag arrived, their first words were: “Well, Lewis, do you think our bridge will stand the test today?”

Wernwag smiled and replied: “Yes, gentlemen, it will.” Then he led them out on the new-laid planking and showed them the blocks and wedges on which the arches rested. They were all loose: Wernwag had knocked them free himself, and since the previous day the bridge had been standing alone. The huge span was aptly named “The Colossus.” It stood for 26 years before being destroyed by fire in 1838.

The Colossus made Lewis Wernwag’s reputation, and for the next quarter century he was seldom without contracts to build covered bridges. Moving to Harpers Ferry, Virginia, in 1824, he took his designs into the fast-developing country west of the Alleghenies, and his sons built specially designed Wernwag arch bridges on the turnpikes of Ohio, Kentucky, and Indiana.

A third early builder was Theodore Burr of Torringford, Connecticut. A self-taught housebuilder and millwright, he put up several experimental bridges before finally concentrating on a simple arch, stiffened with timber bracing and supporting a level roadway. Burr’s were the first bridges of any size to cross such rivers as the Hudson, the Mohawk, the Delaware, and the Susquehanna.

An easygoing optimist, Theodore Burr was not awed by having four big bridges across the Susquehanna all under construction at once. He even bid on a fifth, at Columbia-Wrightsville, Pennsylvania. Burr’s proposal for a 5,620-foot span—more than a mile of wooden trusses—was made on a piece of scrap paper. He promised to construct the piers and abutments for $66,000 and the frame, “or superstructure,” for $54,000, to secure the bridge from the weather for $8,900, and to floor it for another $8,500. At the bottom he added: “Superintendence, say $6,450.”

Burr’s bid was a bit high, and the job went to another Connecticut builder, Jonathan Walcott. Thus Burr lost out on the distinction of erecting what was to be the longest multiple-span covered wooden bridge ever built in the world. He had to be satisfied with building the longest with a single span.

This was at McCall’s Ferry, Pennsylvania, a narrow constriction in the Susquehanna where the water ran 150 feet deep. Since scaffolding could not be driven this deep, the resourceful Burr pinned the span together on land and started to move it into position on floats. When, in the dead of winter, the river froze tight, he finished the job by skidding the arch into place on the ice. To secure manpower, he played up sectional rivalry between the counties on either side of the river, and induced the farmers who would ultimately pay for using the bridge to help him erect it. When McCall’s Ferry Bridge was finished, it had a clear span of over 360 feet. Even today’s laminated wooden arches, prefabricated and lifted aloft by derricks in the construction of huge airplane hangars and public arenas, have not yet equaled the length of Burr’s mighty arch of 1815.