Design and Construction of Modern Steel Railway Bridges

John F. Unsworth

• Éditeur: CRC Press
• Année: 2017
• ISBN:
  9781351647106
• Édition: 2
• Sujet: Technology & Engineering
• Sous-sujet: Civil Engineering

This new edition encompasses current design methods used for steel railway bridges in both SI and Imperial (US Customary) units. It discusses the planning of railway bridges and the appropriate types of bridges based on planning considerations.

1

History and Development of Steel Railway Bridges

1.1INTRODUCTION

The need for reliable transportation systems evolved with the industrial revolution. By the early 19th century, it was necessary to transport materials, finished goods, and people over greater distances in shorter times. These societal requirements, in conjunction with the development of steam power^*, heralded the birth of the railroad. The steam locomotive with a trailing train of passenger or freight cars on iron rails became the principal means of transportation. Accordingly, as transportation improvements were required, the railroad industry became the primary catalyst in the evolution of materials and engineering mechanics in the latter half of the 19th century.

The railroad revolutionized the 19th century. Railroad transportation commenced in the UK on the Stockton to Darlington Railway in 1823 and on the Liverpool and Manchester Railway in 1830. The first commercial railroad in the United States was the Baltimore and Ohio (B&O) Railroad, which was chartered in 1827.

Construction of the associated railroad infrastructure required that a great many wood, masonry, and metal bridges be built. Bridges were required for live loads that had not been previously encountered by bridge builders.^† The first railroad bridge in the United States was a wooden arch-stiffened truss built by the B&O in 1830. Rapid railroad expansion and increasing locomotive weights, particularly in the United States following the Civil War, provoked a strong demand for longer and stronger railway bridges. In response, many metal girder, arch, truss, and suspension bridges were built to accommodate railroad expansion, which was occurring simultaneously in the United States and the UK following the British industrial revolution.

In the United States, there was intense competition among emerging railroad companies to expand west. Nevertheless, crossing the Mississippi River was the greatest challenge to planned railroad growth. The first railway bridge across the Mississippi River was completed in 1856 by the Chicago, Rock Island, and Pacific Railroad.^§ The efforts of the B&O Railroad company to expand its business and to cross the Mississippi River at St. Louis, MO, commencing in 1839^¶ and finally realized in 1874, proved to be a milestone in steel railway bridge design and construction. Although the St. Louis Bridge^** never served the volume of the railway traffic anticipated in 1869 at the start of construction, its engineering involved many innovations that provided the foundation for long-span railway bridge design for many years following its completion in 1874.

The need for longer and stronger railway bridges precipitated an evolution of materials from wood and masonry to cast and wrought iron, and eventually to steel. Many advances and innovations in engineering mechanics and construction technology can also be attributed to the development of the railroads and their need for more robust bridges of greater span.

1.2IRON RAILWAY BRIDGES

1.2.1CAST IRON CONSTRUCTION

A large demand for railway bridges was generated as railroads in the UK and the United States prospered and expanded. Masonry and timber were the principal materials of early railway bridge construction, but new materials were required to span the greater distances and carry the heavier loads associated with railroad expansion. Cast iron had been used in 1779 for the construction of the first metal bridge, a 30.5 m (100 ft) arch span over the Severn River at Coalbrookdale, UK. The first bridge to use cast iron in the United States was the 24.5 m (80 ft) arch, built in 1839, at Brownsville, PA. Cast iron arches^* were some of the first metal railway bridges constructed, and their use expanded with the rapidly developing railroad industry. Table 1.1 indicates some notable cast iron arch railway bridges constructed between 1847 and 1861.

The oldest cast iron railway bridge in existence is the 14 m (47 ft) trough girder at Merthyr Tydfil in South Wales, which was built in 1793 to carry an industrial rail tram. The first iron railway bridge for use by the general public on a chartered railroad was built in 1823 by George Stephenson on the Stockton to Darlington Railway (Figure 1.1). The bridge consisted of 3.8 m (12.5 ft) long lenticular spans^† in a trestle arrangement. This early trestle was a precursor to the many trestles that would be constructed by railroads to enable almost level crossings of wide and/or deep valleys. Table 1.2 summarizes some notable cast iron railway trestles constructed between 1823 and 1860.

George Stephenson’s son, Robert, and Isambard Kingdom Brunel were British railway engineers, who understood cast iron material behavior and the effects of moving railway loads on arches. They successfully built cast iron arch bridges that were designed to act in compression. However, the relatively level grades required for train operations (due to the limited tractive effort available to early locomotives) and use of heavier locomotives also provided motivation for the extensive use of cast iron girder and truss spans for railway bridges.

FIGURE 1.1Gaunless River Bridge of the Stockton and Darlington Railway built in 1825 at West Auckland, UK. (From Chris Lloyd, The Northern Echo, Darlington.)

TABLE 1.1

Notable Iron and Steel Arch Railway Bridges Constructed during 1847–1916

TABLE 1.2

Notable Iron and Steel Viaduct Railway Bridges Constructed during 1823–1909

Commencing about 1830, Robert Stephenson built both cast iron arch and girder railway bridges in the UK. Cast iron plate girders were also built in the United States by the B&O Railroad in 1846, the Pennsylvania Railroad in 1853, and the Boston and Albany Railroad in 1860. The B&O Railroad constructed the first cast iron girder trestles in the United States in 1853. One of the first cast iron railway viaducts in Europe was constructed in 1857 for the Newport to Hereford Railway line at Crumlin, UK. Nevertheless, while many cast iron arches and girders were built in the UK and the United States, American railroads favored the use of composite trusses of wood and iron.

American railroad trusses built after 1840 were often constructed using cast iron, wrought iron, and timber members. In particular, Howe trusses with wood and cast iron compression members and wrought iron tension members were widely used in early American railroad bridge construction.

The failure of a cast iron girder railway bridge in 1847^* stimulated an interest in wrought iron construction among British railway engineers.^† British engineers were concerned with the effect of railway locomotive impact on cast iron railway bridges, and they were beginning to understand that, while strong, cast iron was brittle and prone to sudden failure. Concurrently, American engineers were becoming alarmed by cast iron railway bridge failures, and some even promoted the exclusive use of masonry or timber for railway bridge construction. For example, following the collapse of an iron truss bridge in 1850 on the Erie Railroad, some American railroads dismantled their iron trusses and replaced them with wood trusses. However, the practice of constructing railway bridges using iron was never discontinued on the B&O Railroad.

European and American engineers realized that a more ductile material was required to resist the tensile forces developed by heavy railroad locomotive loads. Wrought iron^‡ provided this increase in material ductility, and it was integrated into the construction of many railway bridges after 1850. The use of cast iron for railway bridge construction in Europe ceased in about 1867.^§ One of the last major railway bridges in Europe to be constructed using cast iron was Gustave Eiffel’s 488 m (1600 ft) long Garonne River Bridge built in 1860. However, cast iron continued to be used in the United States (primarily in compression members), even in some long-span bridges for more than a decade after its demise in Europe.

1.2.2WROUGHT IRON CONSTRUCTION

Early short- and medium-span railway bridges in the United States were usually constructed from girders or propriety trusses (e.g., the Bollman, Whipple, Howe, Pratt, and Warren trusses shown in Figure 1.2). An example of a Whipple truss is also shown in Figure 1.3. US patents were granted for small- and medium-span iron railway trusses after 1840, and they became widely used by American railroads. The trusses typically had cast iron or wood compression members and wrought iron tension members.^¶

FIGURE 1.2Truss forms used by railroads in the United States.

FIGURE 1.3Whipple truss span. (Courtesy of the author, Canadian Pacific Engineering.)

The wooden Howe truss with wrought iron vertical members (patented in 1840) was popular on American railroads up to the 1860s.^* The principal attraction of the Howe truss was the use of wrought iron rods that did not permit the truss joints to come apart when diagonal members were in tension from railway loading. However, the Howe truss form is statically indeterminate, and, therefore, many were built on early American railroads without the benefit of applied scientific analysis.^†

The first railway bridge in the United States constructed entirely of iron was a Howe truss with cast iron compression and wrought iron tension members built by the Philadelphia and Reading Railroad in 1845 at Manayunk, PA. Iron Howe trusses were also constructed on the Boston and Albany Railroad in 1847 near Pitts...