Roads and Bridges

3 Key excerpts on "Roads and Bridges"

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  eBook - ePub

  Bridge Engineering

  Classifications, Design Loading, and Analysis Methods

  • Weiwei Lin, Teruhiko Yoda(Authors)
  • 2017(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  Fig. 1.2 are also typical bridges according to above definition. Bridges are important structures in modern highway and railway transportation systems, and generally serving as “lifelines” in the social infrastructure systems.

  Fig. 1.1 The Bridge of Sighs, Cambridge, the United Kingdom. (Photo by Lin.)

  Fig. 1.2 A flyover in Osaka, Japan. (Photo by Lin.)

  Bridge engineering is a field of engineering (particularly a significant branch of structural engineering) dealing with the surveying, plan, design, analysis, construction, management, and maintenance of bridges that support or resist loads. This variety of disciplines requires knowledge of the science and engineering of natural and man-made materials, composites, metallurgy, structural mechanics, statics, dynamics, statistics, probability theory, hydraulics, and soil science, among other topics (Khan, 2010 ). Similar to other structural engineers (Abrar and Masood, 2014 ), bridge engineers must ensure that their designs satisfy given design standard, being responsible to structural safety (i.e., bridge must not deform severely or even collapse under design static or dynamic loads) and serviceability (i.e., bridge sway that may cause discomfort to the bridge users should be avoided). Bridge engineering theory is based upon modern mechanics (rational knowledge) and empirical knowledge of different construction materials and geometric structures. Bridge engineers need to make innovative and high efficient use of financial resources, construction materials, calculation, and construction technologies to achieve these objectives.

  1.2 Bridge Components

  1.2.1 Superstructure, Bearings, and Substructure

  Structural components of bridges are based on parametric definitions involving deck types and various bridge properties. Bridge structures are composed of superstructure, bearing, superstructure, and accessories.

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  Bridges

  Their Engineering and Planning

  • George C. Lee, Ernest Sternberg(Authors)
  • 2015(Publication Date)
  • SUNY Press

    (Publisher)

  gap that the bridge crosses, a river most readily comes to mind, but it could just as well be a channel, lake, estuary, or the like. Or it may be a chasm, canyon, mining pit, ice crevice, or space between buildings. All these taken together still form a minority of the gaps that bridges cross. Many of the rest are the spaces between the raised sides of a roadway or railway. The curved ramp that raises or lowers traffic at highway interchanges is a bridge, too. So is the elevated highway, sometimes known as a viaduct, which spans the gap as it traverses a row of piers, sometimes casting its shadow over another highway running below.

  That to which the bridge affords passage—well, it is people, vehicles, and the goods they carry, perhaps with livestock tagging along. Some bridges are solely for pedestrians and bicycles; a large number are for railways. In present-day America, that to which the bridge gives passage is overwhelmingly automobile traffic. Unless we specify otherwise, when we say “bridge” in this book, we mean one primarily meant to carry motorized road vehicles, though it may carry pedestrians and trains in addition.

  The things that cross have weight and momentum. To afford them passage, the bridge must consist of an assembly of parts—a structure—that supports the forces acting on it. The structure must carry its own weight, stand up to the loads vehicles impart to it, and resist the forces of winds and waves and of the occasional errant barge that hits a pier. Those who would like to be informed about bridges should be able to understand the basics: the thinking by which engineers decide which kind of structure will safely carry the loads imposed on it.

  THE BRIDGE DECISION

  Even in a road transportation system as large as America’s, we have far more bridges than most would guess, some 600,000 in fact. Every 500 or so Americans owns a bridge, or better put, each American owns a share in the nation’s vast bridge portfolio. And that means many decisions have to be made about bridges, whether to build them, upgrade them, or close and replace them. At many places in America, every few years, citizens and their representatives, along with expert advisers, have to make such decisions.

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  Field Guide to Appropriate Technology

  • Barrett Hazeltine, Christopher Bull(Authors)
  • 2003(Publication Date)
  • Academic Press

    (Publisher)

  If roadwork must be done during the rainy season, use the driest soil that can be found. Allow soil taken from drainage ditches to dry before using it on roads. Bail standing water out of holes before refilling the holes.

  REFERENCES

  Blythe David K. Understanding Low-Cost Road Building . Technical Paper #45 Tel: 703-276-1800. Fax: 703-243-1865. Washington, DC.: Volunteers in Technical Assistance. 1986. http://[email protected] .

  de Veen J.J. The Rural Access Roads Programme: Appropriate Technology in Kenya . Geneva, Switzerland: International Labor Office; 1980.

  Edmonds G.A., Howe J.D.F.G. Roads and Resources: Appropriate Technology in Road Construction in Developing Countries . London: Intermediate Technology Development Group; 1980.

  International Labor Office. Guide to Tools and Equipment for Labour-Based Road Construction . Geneva, Switzerland: International Labor Office; 1981.

  Jackson Ian. Handbook of Fundamentals of Low-Cost Road Construction . Awgu, Nigeria: Community Development Training Center; 1955.

  Weldon K. Designing Coal-Haul Roads for Good Drainage . Berea, Kentucky: U.S. Forest Service, Experimental Station; 1960.

  SMALL-SCALE BRIDGES

  Bridges are needed, of course, to span rivers or gorges. In the United States they are commonly used to carry one road over another, but such applications are hardly small-scale technology. An alternative to a bridge for crossing a river is a ford—a hard surface under the water that can be negotiated on foot or by vehicles. Fords are discussed in another article in this chapter. Ropeways are a type of bridge used in mountain areas, and some bridges are constructed from arches. There are articles on ropeways and arches in the Construction chapter.

  Wood, steel, and concrete are used for bridges. Concrete usually lasts much longer than wood, and it is cheaper than steel. Information on making concrete is provided in an article in the Construction chapter.

  TYPES OF BRIDGES

  The four basic types of freestanding bridges are beam, arch, truss, and suspension (see Figure 28

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