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chapter two

THE EVOLUTION OF COVERED BRIDGE DESIGN

The Philadelphia and Baltimore Railroad’s great rail bridge crossing the Susquehanna River between Havre de Grace and Perryville, Maryland, was near completion on July 26, 1866, when a powerful storm swept down the river valley and completely destroyed the 3,195-foot 13-span crossing. The series of tall Howe trusses reinforced with massive quadruple arches carried each of the 250-foot spans on piers set in water as deep as 40 feet. Because many nearby structures were untouched, the winds—whether straight line or a tornado—apparently lifted the bridge at least three feet before dropping it into the water. Immediately, work crews began securing the remains in preparation for rebuilding the spans in part with salvaged timber. (Library of Congress Prints and Photographs Division, Washington, DC, 20540/Frank Leslie’s Illustrated Newspaper, December 22, 1866, p. 217)

THE PLANNING, PREPARATION AND DESIGN OF A COVERED BRIDGE

In Canada, just as in the United States, old covered bridges today are being rebuilt—and even new bridges being constructed—using designs and methods that harken back to those employed in the nineteenth century. However, sophisticated engineering and methods of assembly now have reduced the hardships once endured by carpenters and masons. Québec’s Powerscourt Bridge had deteriorated badly by 2009 and was closed to traffic when it was decided to refurbish the entire structure. The photo shows the renewed trusses for one span back on the abutment and pier. (Gérald Arbour, 2009)

During the last years of the colonial period and into the first decades of the nineteenth century—roughly from 1760 to 1820—the relatively few men with knowledge of timber framing were called upon to meet unprecedented engineering challenges. None had formal training in civil engineering generally nor bridge construction in particular, and the science of stress analysis in bridge design was still decades away. What they had was common sense, experience, and a bold, creative streak. To that we might add generous doses of bravery and what some might even call “chutzpah.” A few, like Thomas Pope, emphasized the “bold, creative streak” over common sense—he proposed to span the East River with a monumental 1,800-foot wooden arch that would join the cities of New York (now Manhattan) and Brooklyn and even mentioned one over the Hudson River—but most men recognized both the limitations of the materials and their own abilities.

The previous chapter documented what is known of the early history of American timber bridge building, introducing many of the key players. The present chapter explores the process of planning the construction of covered timber truss bridges, the builders, and their many truss designs.

BUILDING A COVERED BRIDGE INVOLVES AT LEAST THE FOLLOWING STEPS.

1 Proposing and financing a bridge

2 Engaging builders for both abutments/piers and superstructure

3 Designing all aspects of the structure: abutments, piers, trusses, deck system, lateral bracing, roofing, siding, and roadway

4 Steps in the construction of the foundations and superstructure

5 Maintenance

6 Obsolescence and decline: the changing fate of covered bridges

Proposing and Financing a Bridge

Essentially, there were two ways to get a bridge built, either by private initiative or by a government body. Only gradually during the nineteenth century did governments take on the responsibility for building and maintaining bridges. Before that became common, bridge building was mostly left to private businessmen hoping not just to solve a transportation problem but also to turn a profit from tolls. Although we know little about bridge building before the advent of companies, we find pieces of evidence here and there. Frances Manwaring Caulkins’ History of Norwich, Connecticut (1874) provides an unusual amount of information on early bridge building: “The earlier bridges were built and kept in order by the inhabitants as highway work. In April, 1717, a petition was presented to the General Assembly ‘for assistance in building a cart bridge over Showtucket [Shetucket] at the falls’ . . . it is probably that this first bridge over the Shetucket was built in the usual way, by a general turn-out of the inhabitants” (p. 343).

Later, she refers to another incident—to be explored more fully further on because it involved a bridge building accident—and writes: “A large party of the inhabitants had assembled to assist in raising the bridge, which was 20 feet high and about 250 feet in length” (p. 343). If these practices were widespread, this pattern probably prevailed throughout the colonies, reminding us of today’s tradition of “barn raisings” among the Amish. Such bridges had to have been simple if ordinary citizens could construct them.

As the century progressed and the growing towns and cities required ever more substantial bridges to allow the transport of goods and mail, and travel for people over the colonies’ major rivers, it was necessary to form companies that in turn hired reputable builders, often selected from several competing proposals. After independence, virtually all of the substantial bridges spanning, for example, the Hudson, Merrimack, Schuylkill, Delaware, Mohawk, and Susquehanna rivers, required the formation of companies and approval by the state legislature. Similarly, the legislatures had to approve the formation of companies for canals, turn-pikes, and other public improvements. The fact that a bridge company was authorized, however, did not mean the bridge was actually built. The bills included toll rates for passage. Those for the Permanent Bridge in Philadelphia ranged from one cent per foot passenger, riderless horse, or head of cattle to twenty cents per four-wheeled pleasure carriage drawn by four horses to $1.35 for a “carriage of burden” weighing the maximum load allowed of six tons.

Philadelphia’s other great bridge, the Lancaster-Schuylkill Bridge, began with an Act of Incorporation approved by the legislature and governor on March 28, 1811, the company beginning with 800 shares at $50 each, for a total of $40,000. By June, the company had elected officers and began advertising for proposals. Eventually, they contracted with Lewis Wernwag to build a single-span bridge later known as “The Colossus.” All of Theodore Burr’s bridges were financed and built by companies, though sometimes there was a considerable time delay between formation of the company, its financing, and completion of the project. Indeed, that is precisely the problem encountered by the companies that hired Burr. As he took on more and more projects requiring increasing cash flows to pay for materials and workers, the companies became reluctant to make advance payments because of endless delays and Burr’s peripatetic work style. As a result, Burr gradually went bankrupt. Additionally, many other companies went bankrupt when their all too new bridges succumbed to one of the annual spring floods or ice jams, and bridges could not be insured against these “acts of God.”

Most early covered bridges were built by entrepreneurs hoping to turn a profit by charging tolls. This necessitated having a toll booth on one end and hiring someone to collect the money. (NSPCB Archives, R. S. Allen Collection)

Although the Cornish-Windsor Bridge spanning the Connecticut River is mostly within New Hampshire and belongs to the Town of Cornish, its earliest toll booth stands on the Windsor, Vermont, side. (A. Chester Ong, 2010)

Although government responsibility for building bridges developed slowly, the National Road, started in 1811, was exceptional because of extensive federal investment. Wernwag’s bridge over the Ohio River at Wheeling, built in 1818 as a key section of the National Road, was discussed in Chapter 1. When the National Road reached Zanesville, Ohio, in 1830, the federal government was still funding the project, but within four years, in 1834, they decided to delegate the funding for the project to the individual states. The most unusual bridge on this route, which later became US 40, was the “Y Bridge” in Zanesville, so-called because it crossed the Muskingum River at its confluence with the Licking River, offering travelers a choice of left or right turns at the center.

The National Road had to cross two rivers in Zanesville, Ohio, where the Muskingum River meets the Licking River. Pictured is the third Y Bridge, built in 1832. The first, in 1813, was an open trestle, but the second, of 1819, was covered. (Ohio Historical Society Archives)

The covered wooden Y Bridge (background) in Zanesville, Ohio, carried the National Road US 40 until 1900 when it was replaced by a concrete bridge. The steel rail bridge in the foreground is no longer in existence either. (Van Tassel, 1901)

The earliest bridge at this site was built by Rufus Scott in 1813, long before the National Road, as a simple trestle bridge. Short-lived, the bridge was damaged by a flood in 1815 and then succumbed to rot, falling into the river in 1818. A second bridge was built in 1819, this time a timber truss bridge with—according to an engraving on a Muskingum Bank of Zanesville five dollar bill—an arch-like shape, suggesting a design akin to those used by Palmer. Built by a private company about which little is known, the bridge continued to serve the now established and increasingly busy National Road. When ice damaged the structure during the winter of 1831, one of the owners, Ebenezer Buckingham, joined his son Catharinus to form a new company. Young Catharinus, only twenty-five, designed a double-lane bridge using multiple kingpost trusses. To overcome concerns about his design, Catharinus built a model, placed 500 pounds on it, then had someone stand on the model as well, thereby winning the contract.

Using newly built piers, construction proceeded during the summer of 1832. On August 20, when young Catharinus was ill with cholera, his father told him that one of the new spans had shifted about six inches. The next day, August 21, while Ebenezer was inspecting the structure, they only realized that the trusses had shifted to the old pier when, according to Norris F. Schneider, “About 3 o’clock the span fell, taking nine men with it. Ebenezer Buckingham and one other man were killed in the fall” (1958: 12). Catharinus successfully completed the bridge, and the company prospered from its relatively expensive tolls. Indeed, by 1849 citizens were complaining about the tolls and the company’s 18 percent dividends, but it was not until 1868 that the state and city jointly agreed to purchase the bridge and relieve the citizens of tolls.

Most toll bridges crossed substantial rivers, and travelers were willing to pay the required tolls to avoid hazardous alternatives. In the case of more modest bridges crossing ordinary streams, the old method of fording might remain an option when water was low, with the result that travelers could avoid tolls. Various patterns developed to get bridges erected. Yet, without a comprehensive history of this aspect of bridge building, we have only anecdotal evidence and a general understanding. These ranged from local initiative with no government involvement to projects that included contributions from local government. There is no consistent pattern. Though all states were divided into counties, the divisions of government below that and their individual responsibilities varied widely. These patterns affected both how bridges came to be erected and how records were kept, the latter being a key source for anyone writing history today. For example, New York State was, and still is, governed by “home rule,” a practice in which local governments may pass laws and ordinances peculiar to their own jurisdictions. As a result, bridges in New York State were usually initiated, financed, and built through local efforts, with or without state approval or financing, and often with minimal record keeping. Thus, it was common in New York for a group of local landowners to band together to finance and build—sometimes themselves—a needed bridge. In other states, mostly farther west, such as Ohio, county government came to control and finance bridge projects. In the case of a state like Oregon or the Canadian province of New Brunswick, where most covered bridges were built after the time of their obsolescence in the east, the highway departments were usually in charge and, as a result, imposed standard designs.

It was customary for county officials to publish a “notice to contractors” when taking bids for a new bridge. This one was published in Coshocton County, Ohio, in 1865, for the Croy’s Mill Bridge. (Terry E. Miller Collection)

Companies, hoping to receive invitations to bid on bridges, advertised in newspapers and magazines. T. H. Hamilton of Toledo, Ohio, was still offering Howe truss bridges in 1885 near the end of the wooden truss era. (Kemp, 2005: 28)

As seen in the County Commissioners’ Journals from 1874, these are the handwritten bids for both superstructure and masonry of the Jacobsport Bridge in Coshocton County, Ohio. The bridge was bid by the lineal foot and stonework by the perch. (Terry E. Miller Collection)

Drawn by Master of Bridges and Buildings, David Hazelton (1832–?), this rare example of a Plan and Elevation blueprint shows a Section drawing for a Town lattice covered rail bridge on the White Mountain Division of the Boston and Lowell Railroad at Warren, New Hampshire. (NSPCB Archives, George B. Pease Collection)

Builders typically used truss models when making their proposals to company managers or officials. This one was made by Theodore Burr to promote his now-familiar truss. (NSPCB Archives, R. S. Allen Collection)

Based on research in Ohio, we know that during the earlier nineteenth century the group wishing to build a local bridge might petition the county commissioners for financial assistance in order to erect a “free bridge.” In these cases, the county might contribute as little as $100 or perhaps $300 towards the effort, the rest of the money being “subscribed” by members of the bridge committee.

A particularly complex case occurred when the citizens of Coshocton in east-central Ohio sought a bridge over the Walhonding River on Hill Street between Roscoe and Coshocton. Though the Ohio Legislature initially authorized the commissioners to build a free bridge using funds from individual subscribers on February 21, 1833, not enough money was raised, and on March 3, 1834 the state amended the act to allow the county to contribute funds. While the bridge project remained in limbo, the state passed yet another act, on January 27, 1836, allowing the commissioners complete responsibility for erecting that and other bridges: “Bridges to be free and to be double track.” To pay for the bridge, they asked for proposals to loan the commissioners between $15,000 and $20,000 (about $375,000 to $500,000 in today’s currency), but no one came forward. At that point, the commissioners appointed General Joseph Burns to find the money, and, believing he would be successful, let a contract for the bridge totaling $19,900. When Burns returned from Baltimore empty handed, the commissioners had to take extreme measures, borrowing $10,000 at 7 percent from the estate of a wealthy man in Brownsville, Pennsylvania, and $10,000 from the Ohio Life Insurance and Trust Company. Because the practice of borrowing money to pay for a “free bridge” seemed risky, the state then passed an amendment allowing for the collection of tolls. We do not know the toll rates or how long tolls were collected, but over the years the county had to pay for many repairs before replacing the Coshocton covered bridge with an iron bridge in 1887.

Engaging builders for stonework and superstructure

As the nineteenth century progressed, county and local governments gradually assumed greater responsibility for public works and were increasingly able to pay for them using tax dollars. But the formal pattern we know today—calling for sealed bids, selecting the lowest bid (that met specifications), inspecting the project upon completion, and paying in full—only developed towards the end of the Civil War (1860–5). After that, at least in counties where full records were kept, the covered bridge building process becomes better known. In areas where local government was responsible for bridge building, record keeping tended to be unsystematic, and over time many documents disappeared. For example, Pennsylvania’s county records provide limited information to researchers since many counties have “cleaned house” by throwing out what records there were. In the case of Ohio and Indiana, at least, the county commissioners kept moderately detailed records. Nineteenth-century journals were handwritten by a secretary, and depending on that person’s diligence, preserved much or little detail. In counties whose records have been most thoroughly researched, we find the commissioners’ journals listing all the bids for both stonework and superstructure, noting to whom the contract was given, and accounting for all (or most) of the payments. What is missing in most cases are the original bids submitted by builders along with any drawings, plans, or specifications they provided.

During the period from about 1865 to the end of the covered bridge era (1890s for most areas but later for Indiana, the South, and the Far West), officials contracted for two matters, the stonework for the abutments and piers and the wooden superstructure. Stonework was bid by the perch and the wooden superstructure by the lineal foot. One perch of stone was 24.75 cubic feet, equivalent to a unit of blocks, 16.5 feet long, 1.5 feet wide, and 1 foot. Bridge foundations generally used large blocks of cut stone quarried locally, but it was also common in some areas of the country for abutments and piers to be made of flat field stones. Stonework was normally laid up dry, that is, without mortar. These were often built on foundations of wooden piles, though little is known of this aspect (see Chapter 3). In areas where stone was difficult to obtain or too expensive, contractors built the bridges on wooden pilings, often replaced later by metal cylinders filled with cement. This was especially so in areas where creek banks and beds were muddy, thus providing a poor base for stone. Although builders preferred abutments built into the bank on either end, when the creek banks rose only gradually, creating a flood plain, the abutments might be built like piers in the water out from the bank, with open approaches of various lengths and designs. Some bridges, for example many in Georgia, had approaches hundreds of feet long.