HISTORIC HIGHWAY BRIDGES OF OREGON

Moffett Creek Bridge (1915), old Columbia River Highway near Bonneville, Multnomah County

Bridge building is a rich and fascinating chapter in the history of technology and engineering. In Oregon, bridge construction also contributed to the general growth and development of the state. An examination of the general history of bridge design and construction and that tradition in Oregon provides a context for the understanding and appreciation of historic bridges.

DEVELOPMENT OF BRIDGE TECHNOLOGY

The history and development of bridge technology is a blend of the adaptation of new materials and improved designs to the three basic types of bridges: arch, beam, and suspension (Figure 2). The concepts behind the basic bridge types have been understood and used for centuries, but until recently the limitations of the available materials severely restricted length, capacity, and design.

FIGURE 2 Basic Bridge Types

There are two major kinds of stress in a bridge: compression, which pushes on or shortens a structural member; and tension, which pulls apart or lengthens a member. The arch acts in compression, the suspension bridge in tension, and the beam or truss (an open-frame beam) in a combination of tension and compression, to support the weight of the bridge and the applied load. The physical nature of bridge materials determines their ability to withstand these stresses. All common bridge-building materials, stone, timber, iron, steel, and concrete, are good in compression. The development of materials that are good in compression and tension, particularly wrought iron and steel, led to rapid advances in bridge design and technology in the mid-19th century.

Early bridge builders generally used whatever material was readily available. The first bridges of primitive man were probably crude stone slabs or logs laid over narrow chasms. In Asia and South America, suspension bridges made of vines or ropes of relatively long length were used. The nature of the material, as well as the current fashion and style, determined the design. Stone, for instance, was found to be naturally strong in compression, but with little or no strength in tension, and consequently made a poor beam structure. When properly crafted, however, it allowed for the construction of exceptionally strong and durable arches. Stone also proved an excellent material for foundations and piers. However, the many deficiencies of masonry construction, such as the massive expenditures of time and effort, the scarcity of appropriate stone, the unsuitability of many sites for short-span arches, and the need for skilled craftsmen, eventually forced man to seek more economical construction materials.

Timber, though obviously not as strong or durable as stone, has both compressive and tensile strength. This advantage, along with its almost universal availability, made wood a good choice as a bridge construction material. The length and quality of available timbers, however, limited individual span lengths in early timber bridges. Though the most basic of design concepts, the timber beam still is in use today.

Arch Bridges

The invention of the arch was a significant step in the history of technology. How and when the arch was discovered remain a matter of conjecture, but both the Sumerians and Egyptians had arched windows and vaults by about 3000 B.C. These early arches, constructed of wedge-shaped stones or bricks, were a great improvement over the earlier-used corbel (or false arch), because arches allowed wider openings and stronger support for the area above the openings. (With a corbel, each course of stones or bricks on either side of an opening is laid projecting slightly further than the one below, until the two sides meet at the crown.) Many centuries passed, however, before the arch was applied on a large scale to the construction of bridges, awaiting the genius of the Roman engineers.

The Romans were the first great bridge builders. The Romans were ambitious builders and constructed thousands of bridges, usually simple timber ones. It was their large stone arch bridges, however, that have endured as testimony to their craftsmanship. The durability of the early Roman bridges is shown by the survival of several 2,000-year-old stone arch bridges in Italy, Spain, and Portugal. The development of the arch bridge by the Romans may be considered the first adaptation of scientific principles to bridge construction.

After the decline of the Roman Empire, few bridges of importance were built in the Western world until the 12th century. Many notable arch bridges were built by religious orders and became sites of shelters and hospices for travelers. Bridges at strategic locations were frequently fortified for defense. The original London Bridge (1209) was lined on both sides by overhanging buildings and also included a chapel.

The Renaissance period transformed the arch bridge. Prominent structures became expressions of the art and architecture of the period. Architects, coming into their own as an artisan class, developed a number of styles—classical, rococo, baroque—and applied these styles to bridges, as well as buildings. Bridges became adorned with detailing, such as open balustrades instead of solid parapets, niches for statues within piers and abutments, chamfered edges on the voussoir stones to emphasize the pattern, and decorative panels and classical columns on the piers and parapets. Some of the most famous historic bridges are arches from the Renaissance period, including the Ponte di Rialto (1591), Venice, and Pont Neuf (1604), Paris. Masonry and masonry-faced arch bridges and aqueducts remained the recognized engineering approach to bridge building until the 18th century.

Truss Bridges

Modern bridge technology began with the advent of the truss bridge. Trusses were commonly used in cathedral construction in the medieval period, and their adaptation to bridges was inevitable. Andrea Palladio, an Italian architect in the 16th century, is credited with first adapting the truss for bridge building and provided truss bridge designs in his Four Books of Architecture (1520). Using the triangle, he designed three forms of trusses built entirely of timber. Swiss and German builders later adapted Palladio's idea or independently invented the truss bridge.

The truss bridge was developed and refined in America in the late 1700s and early 1800s. The first trusses were timber and covered to protect the bridge members from the elements. Famous pioneer bridge builders during this era were Timothy Palmer, Theodore Burr, William Howe, Stephen Long, and Ithiel Town.

Cast iron was used in the construction of arch bridges as early as 1775, but its brittleness and low tensile strength restricted it to compression applications. No significant changes occurred until wrought iron was introduced as a bridge construction material at the beginning of the 19th century. The production of high-grade wrought iron allowed the design and construction of all-metal trusses and composite truss bridges. Composite truss bridges used timber beams for the compression members and iron rods for the tension members.

Several truss designs of the mid-19th century became important in bridge technology, and many continue to be used today (Figure 3). Three of the most notable designs are the trusses patented by Thomas and Caleb Pratt, William Howe and James Warren. The Pratt truss, which placed the vertical members in compression and the diagonal members in tension, has been used in thousands of bridges across America. The Pratt design was best adapted to all-metal construction and spawned a collection of variations, the most important being the Whipple truss (a double-intersection Pratt) and the Parker truss (a Pratt truss with polygonal or curved upper chords).

FIGURE 3 Common Historic Truss Designs in Oregon. (Source: Historic American Engineering Record, National Park Service, United States Department of the Interior, Washington, D.C.) (click on image for a PDF version)

The Howe truss, which placed the vertical members in tension and the diagonal members in compression, was well adapted for use with timber and was widely used to construct covered bridges. The Warren truss, designed by British engineer James Warren, put both compressive and tensile stresses in the diagonal members, simplifying the configuration and allowing for the fewest structural members. This design, first used in 1848, facilitated stress calculation and quickly became the most common of all truss configurations. Virtually all trusses manufactured today are variations of the Warren design.

The first metal truss bridges were constructed of wrought iron, but high grade steel eventually replaced iron as a building material. (Steel is stronger than wrought iron but nearly indistinguishable in appearance.) Prior to 1885, bridge builders relied on wrought iron. Between 1885 and 1895, a boom in the United States steel industry led to the construction of a mixture of wrought iron and steel structures. By the turn of the century, steel had replaced wrought iron for bridge building.

The truss members of the early all-metal bridges were connected with steel pins or bolts (Figure 4). These pin-connected bridges had the two-fold advantage of easy on-site construction and reduction of stress at the joints because the pins were free to rotate. Pin connections also facilitated the relocation of bridges, a common situation for many trusses, because of the ease of disassembly and assembly. However, the flexibility of the joints meant swift wear of the pins and truss members. The rigid riveted joint was developed at the beginning of the 20th century and increased both the load capacity and the service life of metal bridges. By about 1915, the riveted joint completely displaced pin connections.

FIGURE 4. Truss Connections. Left: Riveted gusset plates form rigid truss joints which decrease the wear on individual bridge members and extend the service life. The riveted joint made the pin-connected joint obsolete. Right: Pin connections allow easy on-site truss assembly and are generally found in Oregon only on bridges constructed prior to 1915.

Suspension Bridges

The suspension bridge (Figure 5) was evolving at the same time as the development of the truss in the 19th century. Iron chain suspension bridges were used in the Orient as early as the 7th century and in Europe by the mid-18th century. In the early forms, the roadway decking was laid directly on the cables or chains with little or no stabilization. In 1801, an American, James Finley, constructed the first suspension bridge to suspend a level roadway beneath the chains and later patented a bridge of wire cables.

FIGURE 5. A suspension bridge across the Willamette River was built in 1888 at Oregon City. One of only a few large suspension bridges in Oregon's bridge-building history, the narrow bridge was replaced in 1922 by a steel arch span.

French, American, and Swiss engineers were quick to utilize Finley's ideas. The Menai Straits Bridge, constructed in 1826 in North Wales by Thomas Telford, expressed the importance of the suspension concept with an unprecedented 580-foot span. In 1834, a suspension bridge with a clear span of 810 feet was erected at Fribourg, Switzerland. The suspension bridge was established as the dominant choice in situations where long spans were required. By comparison, arch bridges of the same era rarely exceeded 200 feet in span, while trusses were capable of a span of about 400 feet.

Charles Ellet designed and constructed a suspension bridge across the Ohio River in 1848 with a span of 1,010 feet. The 1,595-foot Brooklyn Bridge, a monumental engineering feat, was constructed between 1867 and 1883 by John A. Roebling and his son Washington. Since that time, advances in cable technology have allowed suspension bridges to span unprecedented lengths. The world's longest bridge span is currently the main span of the Humber Estuary Bridge, between Hessle and Barton, in England, at 4,626 feet. Opened in 1980, the suspension bridge has twin towers, 533 feet tall.

Moveable Bridges

Moveable bridges were developed in response to the need for providing high or unlimited vertical clearance for river navigation. The three general types of moveable span bridges are the swing bridge, balanced on a central pier and rotating about a vertical axis; the vertical lift, which raises vertically in a horizontal position; and the bascule, developed from the medieval drawbridge, which swings upward (Figure 6).

FIGURE 6. An early small bascule bridge in Oregon was the John Day River Bridge, constructed on the Lower Columbia River Highway near Astoria, Clatsop County, in 1918. The timber truss bascule opening span was flanked by two timber truss covered spans.

Moveable bridges underwent rapid change as technology advanced in the 19th century. When the railroads and canal systems spread across the United States in the 1830s, the demand for moveable span bridges increased correspondingly. The early moveable bridges were all swing designs. Five bridges built across the Charles River in Boston in the 1830-40 period were among the earliest swing spans and consisted of crude timber trusses hinged at one corner. The center pivot swing design was developed about 1850 and was used almost exclusively until the end of the century.

Around 1890, practical methods of counterbalancing the enormous weight of the span and refinements to the electric motor led to the development of the modern lift and bascule bridges. When the bascule and lift spans were introduced, the swing span tended to disappear because the new moveable types opened faster. The first major lift-span bridge in the United States, the South Halstead Street Bridge in Chicago, was built in 1892. It had a 130-foot moveable span which could be raised 155 feet. The first bascule appeared in its modern form in Chicago in the following year on the Van Buren Street Bridge.

Reinforced Concrete and Modern Bridges

While engineers were refining and perfecting the various forms of arch, truss, suspension, and moveable bridges in the 19th century, the development of steel and reinforced concrete set the stage for another revolution in bridge design. Concrete had been widely used in piers and foundations, and steel soon dominated truss construction because of its increased strength. It was, however, the blend of steel and concrete that allowed bridge construction to add new dimensions and designs. The plasticity inherent in concrete was combined with the strength of steel to form a structure of virtually any configuration.

Reinforced concrete was initially used to refine the arch bridge. The first use of reinforced concrete for bridge construction in the United States was the Alvord Lake Bridge (1889), a small arch structure in Golden Gate Park, San Francisco, still in use today. This new material allowed for extremely flat arch configurations and greatly increased span lengths. Bridge designers quickly responded to the capabilities of reinforced concrete and produced imaginative and graceful designs able to bridge virtually any site. These expressive combinations of engineering and art are seen in the work of Robert Maillart (Switzerland) and Eugene Freyssinet (France). In Oregon, state bridge engineer Conde B. McCullough designed outstanding reinforced concrete arch spans.

The reinforced concrete arch designs were modified as construction and labor costs rose and artistic styles changed during the 20th century. Ornamentation on the structures slowly disappeared, and bridges with clean, simple lines appeared. Economy of materials became a primary concern, particularly during World War II. The new bridges created an aesthetic standard of their own, expressed in the overall concept and flow of a design and its harmony with the environment.

In addition to the arch, reinforced concrete was also introduced as a building material at the beginning of the 20th century for slab, beam, and girder bridges. Steel and concrete slab, beam, and girder bridge designs have become the predominant choice for most contemporary structures, including the new generations of precast concrete box girder bridges.

BRIDGE BUILDING TRADITION IN OREGON

For the most part, bridge building in Oregon followed the trends and developments occurring in bridge technology across the nation. However, Oregon's network of large rivers, estuaries, and creeks provided the need and opportunity for a large number of bridges, and a rich bridge-building tradition has resulted (Figure 7).

FIGURE 7. Typical of the early metal high truss bridges in Oregon is this span across the Rogue River at Grants Pass, circa 1890. (Photograph courtesy of the Josephine County Historical Society.)

Pioneer Settlement and Early Development, 1840-1870

From the earliest times, the people of Oregon, Indian and pioneer alike, used water transportation whenever possible. When the Lewis and Clark Expedition arrived in 1805, the Columbia River was already an important transportation route with hundreds of dugout canoes, some splendidly carved, plying the river.

Until 1841, overland migration to Oregon was negligible, being mostly adventurers, explorers and hunters, a few of whom remained and settled, and a small number of missionaries. The major settlement awaited the opening of Oregon's premier "highway"—the Oregon Trail. From 1841 to 1869 approximately 350,000 people immigrated to Oregon on the Oregon Trail. Caravans of covered wagons made the 1800-mile trek across the western half of the continent from Independence, Missouri, to Oregon City in the Willamette Valley, in about five months. Major rivers and streams were forded or crossed using small crude boats. At The Dalles in eastern Oregon the hardy immigrants came to the end of the overland trail. The imposing gorge of the Columbia River was impassable for wagons. Livestock had to be driven over the Cascade Range, the wagons dismantled and the last 100-mile leg of the journey made by raft or Hudson's Bay Company bateaux on the Columbia River to Oregon City and the Willamette Valley. The Barlow Trail, a land alternative to the Columbia River route, was blazed over the Cascades south of Mount Hood in 1845.

Bridge construction was not initially a major interest in the Oregon Country. The settlers were more concerned with survival, building cabins and fences, and breaking ground. Water transportation on the Willamette River, the Columbia River, and other streams was convenient. Canoes and rowboats were the first vessels. Keelboats were introduced in 1846, and steamships began regular service in the 1850s.

Ferries were essential to transportation in early Oregon before bridges spanned the major waterways. These ferries were usually operated as a private enterprise and many continued in operation well into the 20th century. The earliest recorded ferry operation was built by Jesse Applegate in 1844 across the Willamette River, north of Salem at the Willamette Mission. Switzer's ferry was established in 1846 across the Columbia River from Fort Vancouver, and there were ferries across the Willamette River at Portland as early as 1848. In addition, a ferry that figured prominently in Oregon history was Olds' ferry across the Snake River, established in 1862. (The existence of Ferry streets in many Oregon towns and cities attests to the large number of early ferries.) Today only three ferries remain in service in Oregon. These are all county owned and ply the Willamette River at Buena Vista, Wheatland and Canby. A Washington ferry still crosses the Columbia River between Cathlamet, Washington, and Westport, Oregon.

Land transportation in the 1840s and 1850s was limited largely to horseback and ox-drawn wagon. Short roads only led from the farms to the nearest river landing. As the population of Oregon increased in the late 1840s, the need for roads and bridges became apparent. One of the early actions of the Provisional Government (1843-48) was to appoint a commission to establish roads. A number of routes were opened and improved through public subscription. The government also authorized the incorporation of several toll bridge companies (Figure 8). A few years later after Oregon became a territory, the provisions of an 1849 act placed bridge construction under the aegis of county governments. Each county court was empowered to determine what bridges would be built and maintained at the expense of the county.

FIGURE 8 Tool bridge rates fixed by the Oregon Provisional Government in Decemer 1845. (Source: Lee H. Nelson, Oregon Covered Bridges, Portland: Oregon Historical Society, 1976.)

With Oregon statehood in 1859, the legislature set up a system of county road districts in which supervisors and appraisers laid out county roads, assessing the cost by taxation. Dozens of requests for public roads and bridges were filed with the county courts, and their construction costs became a major portion of early county budgets. (Federal aid for Oregon's road system was scant and primarily in the form of grants for military purposes during this early period.) Many counties opted to license ferry operations rather than build bridges. With the gradual settlement of Oregon, however, bridges began to displace fords and ferries at points of heaviest traffic, but only where economic and most needed.

The first bridge in Oregon is unknown, but it may be assumed it was small, simple and undistinguished. A few log bridges were built in the Oregon Country before the migrations of the 1840s, but most were built during or after this period (Figure 9). Records indicate that a bridge was constructed on Main Street in Oregon City in the mid-1840s, followed by a second bridge to the island mills in 1847. A bridge spanning Dairy Creek in Washington County was built in 1846, and a bridge was erected across the Yamhill River at Lafayette in 1851. Subsequent bridges were built over Marys River near Corvallis in 1856, across the Tualatin River near Moore's Mill in 1859, over the Luckiamute River in 1863, and over the Long Tom in 1870. A covered timber span was built across South Mill Creek on Commercial Street in Salem in 1862, one of the first references to a covered bridge in the state.

FIGURE 9. This timber and wrought iron queenpost truss is representative of early bridges in Oregon. Inexpensive, made of local materials, and constructed by local builders, these timber bridges were functional if not always long-lasting. (This bridge spanned Camas Creek near Ukiah, Umatilla County, and was built about 1900.)

Bridges were attempted as early as 1859 in the Rogue River section of southern Oregon. Sherar's Bridge across the Deschutes River in central Oregon was first constructed in 1858, and subsequently rebuilt several times due to periodic flooding. Timber structures were constructed across the Upper Molalla in 1861, across the Clackamas at Estacada in 1862, and across the Yamhill at Sheridan in 1865. These bridges are the earliest recorded bridges in the state.

The Railroad Era, 1870-1885

Railroad construction in the United States had a major impact on bridge building and construction. The railroads required bridges which could withstand the stress of extremely heavy loads, traveling at relatively high speeds. Certain truss forms and materials were found to perform better than others under these conditions. The railroads also required bridges which could be built cheaply and quickly. In a short period, railroad bridges proliferated and many new bridge forms were developed. Initially, many railroad bridges were timber trestles or trusses. Metal, however, was introduced in the construction of new bridges because of the structural limitations of wood and its flammability.

The 1870s saw the advent of major railroad construction in Oregon. The Oregon and California Railroad, running north and south through the state, began construction in Portland in 1868, finally reaching Ashland in 1887. The next major railroad in Oregon was the Oregon Railway and Navigation Company along the Columbia River, completed in 1883, connecting Oregon with the transcontinental system. These major lines were supplemented by short lines and interurban electric lines.

The first large bridges in Oregon were railroad spans. The Oregon and California Railroad built the first bridge across the Willamette River at Harisburg in 1871. The structure was a covered timber Howe truss with a drawspan for river navigation. The total length was 770 feet, including approaches. An equally impressive timber structure was built by the same railroad across the North Umpqua River near Roseburg in 1872. This bridge was over 1,000 feet long and consisted of five Howe trusses and trestle work. The first major steel bridge in the state was the original Steel Bridge, built across the Willamette River in Portland in 1888.

The oldest surviving bridges in Oregon are railroad structures, including the McKenzie River (Booth-Kelly or Hayden) Bridge at Springfield, built in 1882 and moved to its present location from Utah in 1900 (Figure 10). This bridge is the oldest known bridge in Oregon. Other railroad bridges of the 1880s include a span at Mill City across the North Santiam River, circa 1885, now a public footbridge; and the Armitage Railroad Bridge across the McKenzie River, north of Eugene, which serves on a bicycle route. The Armitage Bridge was built in 1887 and moved to this location in 1907. These bridges are all wrought iron truss spans.

FIGURE 10. The Booth-Kelly Railroad Bridge (also called the Hayden Bridge) across the McKenzie River at Springfield is considered the oldest surviving bridge in Oregon. The wrought iron truss structure was first erected near Corrine, Utah, in 1882 and was moved to its present location in 1900. The Whipple truss and Phoenix columns make it a unique structure.

Catalog Bridges and the Dawn of the Good Roads Movement, 1885-1900

Prior to the turn of the century, high water and flooding caused the repeated destruction of bridges and necessitated quick, inexpensive replacements. For example, catastrophic flooding occurred in 1881 and 1890, and these rampaging floods destroyed dozens of structures. Often a bridge from upstream collided with one downstream, creating a devastating, floating bridge jam. Covered bridges, because of their solid walls and buoyant timbers, were especially susceptible to washout. Fires also took their toll on wooden bridges.

Destruction of an unusually large number of timber bridges in the flood of 1890 hastened a trend toward metal bridges, a trend which was already gaining momentum. Bridge building had become more complex and passed from the domain of the old-style bridge carpenter to companies specializing in light iron or steel prefabricated bridges. While the wooden bridges required frequent maintenance and were expensive to rebuild, iron and steel bridges required little maintenance and were not as apt to wash away. Sharp-talking bridge salesmen used all of their tricks to convince county courts that wooden bridges were dangerous, and therefore must be replaced. Wholesale replacement of wooden bridges followed, until the World War I period.

In Oregon, the late years of the 19th century were the heyday of the bridge companies and their catalog prefabricated bridges. The number of bridges built and the number of bridge companies mushroomed. Some companies were nationally known, although most were local or regional (Appendix B).

The late 1880s and early 1890s saw the beginning of the nationwide Good Roads movement. Initiated by bicyclists demanding smooth surfaced roads, the movement was soon joined by farmers needing better market roads and the federal government interested in good roads for rural mail deliveries. The Office of Road Inquiry was created in the United States Department of Agriculture in 1893 to investigate, educate, and distribute information on road building. (In 1916 this agency became the United States Bureau of Public Roads, the antecedent of the current Federal Highway Administration.)

Considerable interest in good roads also arose in Oregon during this period. An early hint of this concern was revealed in a Good Roads convention held in Portland in December 1896. One of the speakers defined a good road as one that was equally good in rainy weather as in fair weather, one well-drained and not in need of repair. He went on to state that no such road existed in Oregon. Subsequent county petitions to the state and federal governments indicated that good roads and bridges had a high priority in Oregon.

The 1885-1900 period saw the initial construction of large highway bridges in Oregon. After sixteen years of agitation for a highway bridge across the Willamette River in Portland, the first Morrison Street Bridge was built in 1887 (Figure 11). The Madison Street Bridge (1891) and the original Burnside Bridge (1894) were constructed a few years later. These bridges were either timber or iron trusses with swing spans to accommodate river traffic. A suspension bridge constructed at Oregon City in 1888 joined the Willamette River bridges, one of the few large suspension bridges ever built in Oregon (Figure 5).

FIGURE 11. The first Morrison Street Bridge, a timber structure built in 1887 across the Willamette River in Portland, was replaced in 1905 by a steel bridge (shown in this 1921 photo). The swing span was open, and deck repairs were underway. The Hawthorne Bridge (1910) appears in the background. A third generation Morrison Street Bridge was completed in 1958.

Steel truss bridges were built across the Willamette River at Albany in 1887 and Salem in 1890. (This was Salem's second Willamette River crossing. The first was a timber bridge completed in 1886 and washed away in the big flood of 1890.) On the Oregon Coast, the first bridge over the North Fork of the Coquille River at Burton's Prairie was built in 1881. The first steel truss across the Rogue River was also built during this period at Grants Pass.

Arrival of the Motor Age and the Creation of the State Highway Department, 1900-1920

The rapid acceptance of the automobile drastically changed transportation patterns in Oregon and intensified the need for better roads and bridges. One of the results of this change was the creation of the State Highway Commission and the State Highway Department in 1913.

The State Highway Department significantly changed bridge building in the state and made rapid strides in bridge construction. By statute the new department set up a system whereby the counties and cities could obtain bridge design services from the state at no cost. In addition, a manual on bridge specifications and designs was published in 1916, which helped to ensure a uniform standard of bridge design and contributed to high quality construction.

The United States Congress passed the Federal Aid Act in 1916, which provided funds on a matching basis to the states for road and bridge construction. To match the federal funds, Oregon adopted a gasoline tax in 1919 as a source of income for road purposes. Oregon's lead in the use of gas tax revenue for highway purposes was followed promptly by other states, and within a few years became the main source of highway revenue for all states throughout the nation.

In addition to a surge of construction, the 1900-1920 period witnessed some significant events in the bridge history of Oregon. Several major new bridges supplemented or replaced the existing Willamette River bridges in Portland, including the Hawthorne (1910), Steel (1912), and Broadway (1913) bridges (Figure 12). The Van Buren Street Bridge (1913) was built in Corvallis, and the Center Street Bridge (1918) was constructed in Salem. The largest highway bridge built during this period was the Interstate Bridge (1917) which spanned the Columbia River to connect Portland with Vancouver, Washington. (The first bridge to span the Columbia River between Oregon and Washington was the Spokane, Portland, and Seattle railroad bridge, a swing span completed in 1908.) Most of these highway bridges were steel trusses with some type of moveable span.

FIGURE 12. Bisected by the Willamette River, Portland is a city of bridges. Ten highway bridges cross the Willamette River in Portland, seven of which are seen in this aerial view of the downtown: foreground to background, Marquam (1966), Hawthorne (1910), Morrison (1958), Burnside (1926), Steel (1912), Broadway (1913), and Fremont (1973). Not shown are St. John's (1931), Ross Island (1926) and Sellwood (1925).

Several outstanding reinforced concrete structures were built during this period on the scenic Columbia River Highway in the Columbia Gorge and are among the earliest concrete bridges built by the State Highway Department. These bridges were innovative, frequently of the arch form, and beautifully sited in the Columbia Gorge environment. The bridges are now included in the Columbia River Highway Historic District, listed on the National Register of Historic Places in 1983.

Although timber truss covered bridges had been built in Oregon since the 1850s, the high point of covered bridge construction occurred at the beginning of this century, between 1905 and 1925. Oregon had a maximum of about 450 covered bridges during this period. Today, there are about 50 covered bridges remaining in the state. (A thematic nomination of Oregon's covered bridges was approved for the National Register in 1979. The bridges included in the Oregon Covered Bridges nomination, as well as in the Columbia River Highway Historic District, are presented in the historic highway bridges section of this document.)

"Pulling Oregon Out of the Mud" Era, 1920-1940

The booming economy of the 1920s and the availability of federal-aid matching funds led to a major expansion in transportation facilities in Oregon. Higher speed cars and the increased truck traffic also necessitated changes in road and bridge design. Several major highway routes in Oregon were completed during this period. The Pacific Highway, stretching north and south from Washington to California, was dedicated in 1923. The Columbia River Highway across Oregon's northern border was paved from the coast to The Dalles in 1922. The Oregon Coast Highway, begun in 1914, was essentially finished in 1936, with the completion of five major bridges.

The design and construction of bridges in the state during this period was dominated by state bridge engineer Conde B. McCullough. McCullough's distinguished career with the State Highway Department spanned over 25 years, and he was responsible for hundreds of bridges in Oregon. He left a legacy of fine structures, and his arch bridges, in particular, have achieved the most acclaim and recognition, primarily because of their beauty. (Appendix B contains biographical information on McCullough and other significant bridge designers in Oregon.) McCullough's skill as an engineer paralleled his concern for aesthetics, and he was consistently at the forefront of new developments in bridge design. In 1931, he introduced the reinforced concrete tied arch to the United States with the construction of the Wilson River Bridge in Tillamook County. He was also the first to use the Freyssinet method of arch precompression with the Rogue River Bridge (1931) at Gold Beach.

In spite of the economic effects of the Depression, Oregon built some of its most magnificent bridges during this period with the assistance of federal WPA funding. The era of McCullough's bridge engineering culminated in the completion in 1936 of five major bridges, all crossing rivers or estuaries on the Pacific Coast and all designed to replace ferry service on the Oregon Coast Highway. The bridges—Coos Bay Bridge (North Bend), Umpqua River Bridge (Reedsport), Siuslaw River (Florence), Alsea Bay (Waldport), and Yaquina Bay (Newport)—were built at a total cost of $5.4 million and were financed in part by the Works Progress Administration. These concrete and steel bridges are impressive examples of the structures built during the Great Depression. McCullough was honored posthumously in 1947 when the Coos Bay Bridge, the largest of the five bridges, was renamed and dedicated as the McCullough Memorial Bridge (Figure 13).

FIGURE 13. The Coos Bay Bridge at North Bend was the longest and most expensive of the five Oregon Coast bridges completed in 1936. (This view is during construction in 1935.) The Coos Bay Bridge was dedicated posthumously in 1947 to Conde B. McCullough, Oregon's early outstanding state bridge engineer.

Modern Era, 1940-Present

World War II limited both the funding and materials available for highway and bridge construction in Oregon. Steel was in short supply and was rarely available for bridge building. Federal and local funds were also restricted to essential projects. Oregon relied on its available resources and constructed more than half its bridges during these years from timber. (A notable exception to the timber spans is the steel, tied-arch, triple span structure across the Santiam River between Marion and Linn counties on the Pacific Highway, built in 1946.)

Highway and bridge construction accelerated after the war, but construction monies were scarce. Many of the aesthetic considerations common to earlier bridges were foregone in favor of utility and cost-effectiveness. Steel was once again available to bridge designers, and deck girder and deck truss structures were particularly common in this period.

When the Interstate Highway System was started in the late 1950s, the federal government pumped large amounts of money into road and bridge construction programs. Oregon took this opportunity to revitalize its major highway routes. Reinforced concrete was the primary bridge-building material. Steel was reserved for major structures, such as a second triple arch span over the Santiam River on Interstate 5 (1958) adjacent to the 1946 structure, the Thomas Creek Bridge on the Oregon Coast Highway (1961), and the cantilever truss across the mouth of the Columbia River at Astoria (1966). Steel remained a viable, though expensive, alternative into the 1970s, as evidenced by the Fremont Bridge (1973) across the Willamette River in Portland, a 1,255-foot arch span. (Views of post-1940 construction bridges are in Appendix F.)

The advent of prestressed and post-tensioned reinforced concrete structures, in conjunction with more stable economic conditions, brought about a revival of aesthetic interest in structures. Award winning structures, such as the Chetco River Bridge (1972) on the Oregon Coast Highway in Curry County, and the I-205 crossing of the Columbia River (Figure 14), completed in 1982, demonstrate this new bridge aesthetic and are the latest spectacular additions to Oregon's rich bridge-building tradition.

FIGURE 14. Oregon's latest spectacular addition to its bridge-building tradition is the Interstate 205 crossing of the Columbia River, completed in 1982. Dedicated to Glenn L. Jackson, long-time member of the Oregon Transportation Commission, the twin structures are post-tensioned reinforced concrete box girders, 11,750 feet in length.