Read the following text and make a plan of it. Render the text according to your plan.

A bridge crossing is an engineering structure that provides a safe and reliable passage for traffic and minimises impact on the waterway. Figure 2.1 shows the components of a bridge crossing: (1) superstructure, (2) piers, (3) abutments, (4) substructure, (5) embankments, (6) flood-control dams, and (7) groynes.

Lowland rivers have, as a rule, a clearly shaped low-water mark (8), i.e. the place where a river flows at the lowest point. During the high-water period rivers, overflow their left and right banks (9). As it may be dangerous to the embankments, flood-control dams and groynes distribute, regulate and direct water flow and protect embankments and bridge foundations from bridge scour. Local relief and water levels determine floodplains.

The term “bridge” includes not only the superstructure but the substructure as well (fig. 2.2). The superstructure comprises spans (1) that directly resist the load of the rolling stock. The unsupported length between piers (2) is called a span. Structurally superstructures consist of beams, girders, arches or trusses. The bridge substructure includes abutments, piers and foundations (3). Abutments and piers resist the vertical and horizontal forces of spans, ice and wind. Vertical and slant pier columns carry these loads onto their foundations (3). Foundations resist the loads from the piers and direct them into the foundation beds. Carriages are located between spans and piers to compensate for span deformation caused by loads and seasonal changes as well as temperature variations during the entire day. Bridge engineers have to give careful thought to the dead weight, loads from the rolling stock and pedestrians as well as wind velocity and ice, berthing impact, breaking force, temperature differences and seismic activity for providing strength, rigidity and stability against those potentially destructive forces.

Bridge crossings must provide an unobstructed space between piers for navigation. It is called clear headroom or bridge clearance (5). The distance from the high-water mark to the bridge underside depends on the river’s navigation class. According to navigation regulations, all rivers are subdivided into seven navigational classes. The largest rivers belong to the first class and require clear headroom of 140 m wide and 17 m high.

The most important bridge characteristic is span (6), i.e. the space between the carriages of the neighbouring piers. The suspension bridge over the Humber River in Great Britain holds the world record. As its main span length is 1, 410 m, and has a total length of 2, 200 m. It is suspended between towers, that rise 152 m above their supporting piers, and carries a four-lane highway and pedestrian walkways. The building of the bridge caused much controversy because of the high cost, which exceeded $250, 000, 000 and because the bridge site was not along a heavily trafficked route. Nevertheless, the bridge opened in July 1981 and after more than eight years of construction, it stimulated industrial and commercial development in the area.

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