History of Covered Bridges
Why were bridges covered?
Today covered bridges are considered historical landmarks, romantic structures resembling the past, but what was the purpose of covering these bridges? There were thought to be many reasons why bridges were covered, although not all of these ideas were correct. One explanation was that "the spans were built to resemble barns so farm animals would feel more at home and not stampede as they were driven across the rushing waters." (Adams, 25). Other explanations included: to keep snow off the bridge, "to keep the oiled planks of the roadbed from becoming dangerously slippery in the rain" (Adams, 26), to cover up the unsightly trusses, to provide shelter to travelers caught in a storm, and to provide a place to court your lady and secretly give her a kiss. One real reason for covering bridges was to protect the trusses from the weather because the environment caused bridges to fail sooner. Bridge engineers pointed out "that a housed timber truss span has a life expectancy at least three times greater than one unhoused" (Adams, 27). Due to the wetness of Western Oregon, bridge builders quickly discovered the importance of covering their bridges. "Another important consideration [was] that housing provid[ed] a sort of insulation for the timber, shading it from the sun and maintaining it under more uniform temperature conditions" (Adams, 27). Covering bridges became so ingrained within the minds of people that almost every bridge built was covered even though the cost to do so was higher.
Many of the railroad bridges were not covered; but, when a bridge collapsed under the weight of a passenger train causing it to fall into the river, the Railroad Commission’s report pointed out that this bridge would have lasted longer if it had been covered. The bridge had suffered from rot in the joints. After the accident, all bridges on that particular line were covered.
Another positive reason why bridges were covered was that the roof strengthened the entire structure. "In Washington,…the cross-bracing of a roof…saved many a bridge from the strong northerly winds. Even so, a covered bridge [was] built like a giant wooden box kite. A 200-foot span…[would take] punches from a windstorm equal to a lateral thrust of 100 tons. At other times, weakening [was] inevitable from the constant and almost imperceptible pressure of the wind" (Adams, 27).
These were the determining factors on whether or not a bridge would be covered. With advances in technology, bridges today are covered only for the reason of attracting tourists and paying sightseers.
History of Covered Bridges
Covered bridges can be dated back two thousand years to a time when they were being built in China and even earlier in ancient Babylon (780 B.C.). But the first covered bridge built in America was built in 1804 by Theodore Burr of Connecticut. This bridge spanned the Hudson River in New York and was called the Waterford Bridge, lasting for 105 years. With time, the idea of covering bridges moved west. The first recorded covered bridge (1851) built in Oregon was located in Oregon City; the second (1852) was also built at Oregon City but both bridges were eventually swept away by flood waters in January, 1853. But before there were covered bridges, whether covered or not, there were ferries. Ferries were usually established on the river before bridges and were known for holding a monopoly on the local economy by the prices they charged, especially to buyers and sellers who operated on opposite sides of the river. The public urged the local government to solve this problem by building bridges. Thus, bridge allowances were usually at the top of the list in county budgets due to the number of rivers required to be crossed by the public. "By the 1870s the idea of covering a bridge was generally accepted, though sometimes a county court tried to save the added cost. Irate taxpayers frequently had to file petitions to have a bridge roofed, apparently in an effort to protect their investment. However, most of the substantial bridges were covered at the time of construction." (Nelson, 12).
The increase interest in the building of bridges attracted many carpenters and architects. "The most active and prominent of the Oregon bridge builders from 1973 to 1885 was the firm of A.S. Miller and Sons." (Nelson, 14). The reason for his success was that he "purchased a contractor’s franchise for exclusive rights to use the Smith truss in either Oregon or the Washington Territory" (Nelson, 15). The Smith truss was a much better and longer-lasting form of building compared to the other methods used.
"Among the most important contributions of A.S. Miller & Sons to bridge building in Oregon was the person of Lord Nelson Roney, who in 1875 started his career as a bridge carpenter for that firm. After Roney’s experience with the Millers, he turned professional bridge builder, his opportunity being afforded by the 1881 flood which washed out more than the usual number of spans. ‘Nels’ Roney was probably the most productive covered bridge builder in Oregon’s history, and continued as such until the middle 1920’s, devoting fifty years of his life to the business. Even at the time of his death in 1944, several of his covered bridges stood as evidence of his conservative approach to bridge construction, and the last of many signs bearing the inscription, ‘Built by L.N. Roney,’ was not torn down until 1953" (Nelson, 33).
Nearly a hundred bridges were built by Rodney, most of them being covered. Besides bridge building, he built commercial, educational, religious, public and residential buildings.
With the building of bridges, construction accidents were bound to happen. There are accounts of men falling off bridges during construction, bridges falling down due to weather, and other mishaps. "Such occupational bridge building hazards exist today of course, but they are materially reduced by the safety engineers, union safety requirements, state industrial accident commissions and workmen’s compensation. The nineteenth century bridge carpenter could expect no recompense for loss of time or bodily injury." (Nelson, 39).
Covered bridges served many other purposes besides providing a way to cross a river. Weddings, political rallies, National Guard drills, religious meetings, a night’s sleep for tramps, town meetings, poker parties, election headquarters, sweethearts’ rendezvous, drunken revels, bond rallies, fights and dances, and rainy-day luncheons took place in covered bridges. They also served as good landmarks and advertisement billboards.
Tolls were taken to provide money to pay for upkeep of the bridges. But many times people crossing paid exuberant prices in tolls depending on with what they were crossing. "It was 1887 before Oregon officially freed persons going to church, funeral or election from bridge tolls, then added a new exemption for farmers going from one part of their property to another." (Adams, 20).
Floods washing away expensive bridges caused the redesign of many covered bridges. Many builders began building with a combination of iron and wood trusses. The automobile age also encouraged the building of steel bridges. "Bridge building became more complex, and passed from the domain of the old-style bridge carpenter to companies specializing in light, steel prefabricated bridges." (Nelson, 45). But, with the rapid changes in transportation, even these steel bridges became obsolete within a few years of being built.
With the onset of World War I, wooden bridges again became the ideal due to a lack of steel. The bridges built usually were built with windows, laminated floors, asphaltic wearing surfaces, and interior whitewashing. These bridges had more of an artistic appearance compared to the covered bridges built at earlier times. These "new bridges were so heavily constructed, with considerable cross-bracing and extra safety factors for heavy, modern traffic, that they became as complicated as steel bridges, slower to erect, and nearly as expensive." (Nelson, 48).
Building Methods and Materials
Before Oregon was politically and economically mature, covered bridges were not usually built with longevity in mind. But the builders were very sufficient in using local materials to build their bridges, especially with the abundance of wood. Not much imagination was built into Oregon’s covered bridges. Utility was key.
"On some Oregon bridges the critical joints are cleverly protected, and visual penetration of structural efficiency is thus made possible. Such efforts reduce the barn-like quality and increase the three-dimensional architectural interest. But most bridge carpenters, being neither engineers nor architects, contributed little in the way of structural or architectural innovations; instead they doggedly directed whatever artistic instincts they possessed toward making the portal distinctive. For the most part they succeeded only in constructing an inarticulate floating box." (Nelson, 3).
Wood used for trusses on a bridge had to be straight, lightweight and sound. Red cedar tended to be the best wood to use in construction. Douglas fir was a favorite in the Northwest. "Properly seasoned, it [gripped] nails even more firmly than oak. And metal parts set in it [would] not corrode as quickly as in most other species." (Adams,37). "The Douglas fir of Oregon, so easily obtained, so strong, and of such magnificent dimensions, was the perfect answer to the bridge builder’s problems. One-piece truss chords were common and economical, felled near the site and hewn on the spot." (Nelson, 4). Fastenings were made of the nearest hardwood, preferably oak, maple or black locust, and soaked in linseed oil for preservation and lubrication. These dowel-like nails were then driven through pre-drilled holes.
Andrea Palladio, a classicist Italian architect of the 16th Century, invented the truss, a self-supporting span, which "was economical to build, capable of spanning great lengths and adaptable to the use of short pieces of timber." (Adams,29).
The evolution of the wooden truss is evident in these side views of trusses found in western covered bridges today.
The basic kingpost truss features a center upright post (which gives the truss its name) framed into a triangle formed by the bottom chord and two diagonals. All three timbers are in compression, taking the burden up to the peak of the pyramid….Kingpost trusses are widely used in building construction, but have a serious limitation when used for modern bridges: the heavier the load to be carried, the longer the diagonal timbers must be.
The earliest alternative to impossibly outsized kingpost trusses was the queenpost. It is a stretched out kingpost with two or three uprights instead of one, connected by an upper chord. Eight examples are found in Oregon.
The "Burr-arch" truss, not patented until 1817, took Palladio’s kingpost, extended it, and strengthened it with a wooden arch. For a quarter of a century, covered bridge builders, unsure of the strength of the simple truss alone, would use the composite form of arch and truss much like the cautious man who wears both belt and suspenders.
The Warren truss is merely a series of modified kingposts which appear to form the letter W….it is economical and simple. Larger parts are required than for other types, but any one of them can be removed and replaced easily without disrupting highway traffic. A disadvantage is the combination of compression (squeeze) and tension (pull) stresses on the web members at the center of the bridge.
The Howe truss can be figured out by almost any carpenter or road laborer. All its angle blocks are patterned the same size in an early example of standardization that would have pleased Henry Ford. The metal rods are secured to the top and bottom faces of the chords by means of nuts and washers. These can be tightened at any time to remove the sagging signs of old age.
Thomas and Caleb Pratt patented a combination truss which inverted Howe’s idea by making the diagonals of iron and the compression members of vertical timber. It appears as a series of V’s cut lengthwise rather than Howe’s split A’s. Making use of more iron, it had a strong appeal to safety-conscious railroad bridge builders, who made it a runner-up in popularity to the Howe. Pratt trusses were preferred for short spans, with the Howe and Warren more suited for longer ones. (2, 30)
Covered Bridges Today
Today, many of these historic covered bridges are being restored and protected from destruction. Besides adding charm to a small town or country side, they offer a glance back in history to days gone-by.
---------------------------------
Adams, Kramer A. (1963). Covered Bridges of the West. Berkeley, CA: Howell-North.
Atawalk. [ atawalk@sympatico.ca ]. "Data On Past and Present Covered Bridges." [http://www.atawalk.com/quest.html ]. 1996.
College of New Jersey, The. "The Covered Bridges of the United States." [http://www.tcnj.edu/~drelick2/techdesign/covered.htm ].
[ CoveredBridges<72157.1373@compuserve.com ]. "Oregon’s Covered Bridges." [http://www.mcec.com/~draft/bridges/blueprint.html ].
Department of Transportation, The. [ mdot@state.me.us ]. "Covered Bridges of Maine." [http://www.state.me.us/mdot/maint_op/covered/coverbrg.htm ]. January 6, 1997.
Douglas County. "Covered Bridges of Douglas County." [http://www.co.douglas.or.us/planning/bridges.html ]. 2000.
"Historic Covered Bridges of Georgia"/"Bridge Construction." [http://www.dot.state.ga.us/homeoffs/bridge_dsgn.www/covered/construc.htm ]. 1998.
Indiana Historical Bureau. [ ihb@statelib.lib.in.us ]. "Indiana Historical Bureau." [http://www.statelib.lib.in.us/WWW/IHB/truss.html ].
Lane County. "A Guide To Covered Bridges." [http://www.co.lane.or.us/about/historic/bridge/covered.htm ]. 1997.
Nelson, Lee H. (1976). A Century of Oregon Covered Bridges 1851-1952. Portland, OR: Oregon Historical Society.
Ohio Department of Transportation. [ bhull@odot.dot.ohio.gov ]. "History of Covered Bridges." [http://www.dot.state.oh.us/coverb/history_of_ohio.htm ]. 1999.
Online Highways. [ rob@ohwy.com ]. "Covered Bridge Society of Oregon." [http://www.studyweb.com/Architecture ].
Oregon Department of Transportation. [ james.b.norman@odot.state.or.us ]. "Oregon Department of Transportation Environmental Services; Covered Bridges." [http://www.odot.state.or.us/eshtm/cb.htm ]. 1997.
What Where When. "Covered Bridge Designs." [http://www.studyweb.com/Architecture ]. 1995.
-----------------------
Links:
A Guide to Lane County Covered Bridges; http://www.co.lane.or.us/about/historic/bridge/covered.htm
A tour through the Covered Bridges of Maine; http://www.state.me.us/mdot/maint_op/covered/coverbrg.htm
Blueprints; http://www.mcec.com/~!draft/bridges/blueprint.html
bridges; http://www.washpatourism.org/bridges.html
Covered Bridge Links; http://www.hycoveredbridges.org/links.html
Covered Bridge Trusses in Indiana; http://www.statelib.lib.in.us/WWW/IHB/truss.html
Covered Bridges; http://www.tcnj.edu/~drelick2/techdesign/covered.htm
Atawalk; http://www.atawalk.com/quest.html
Historic Bridges, Oregon Department of Transportation, Environmental Services; http://www.odot.state.or.us/eshtm/br.htm
Historic Covered Bridges of Georgia; http://www.dot.state.ga.us/homeoffs/bridge_dsgn.www/covered/index.htm
History of Covered Bridges; http://www.dot.state.oh.us/coverb/history_of_ohio.htm
Ohio’s Covered Bridges; http://www.dot.state.oh.us/coverb
KATU.com—Outdoor Story; http://local.portland.citysearch.com/story/990513outdoorromance.htm
New York Bridge History; http://www.nycoveredbridges.org/history.html
Oregon’s Covered Bridges; http://www.viser.net/~draft/bridges/bridges.shtml
Oregon’s Historic Covered Bridges; http://community-2.webtv.net/OregonBridges/OREGONHISTORIC
Resources; http://william-king.www.drexel.edu/top/bridge/CBResources.HTML
Study WEB; http://www.studyweb.com/Architecture
Vermont’s Covered Bridges; http://www.virtualvermont.com
Fred J. Becker, Architect
Back