Preparatory works
Construction of the bridge begins with a comprehensive engineering and engineering-geodesic survey. Various measurements are taken. For the future bridge, as a rule, a place with minimal distance between opposite banks of a river, strait, bay or reservoir is chosen. In many cases, this distance is further reduced by creating an artificial embankment towards the opposite bank. In these cases, for unimpeded flow of water and navigation, the fairway (fairway) is deepened by dredgers, over which only the high span of the bridge is built.
In other cases it is economically more advantageous to use natural islands, which can significantly reduce the length of the bridge under construction. If they meet shoals on the way, they either pile up artificial islands and lay the road over them, or build only bridge abutments. However, more often the location of the supports is determined by the length of the future bridge spans, regardless of the depth of the river or strait.
Erection of abutments
There are many ways to build bridge piers, improvement of their designs and invention of new forms and materials for them is a common phenomenon. Bridge footing foundations can be both onshore and underwater, so there are different ways to construct them.
For the former, an excavation is dug and the piles are driven in, a formwork is constructed with a steel armature frame inside, which is then filled with concrete, taking the desired shape and size.
Under water, the excavation for the foundation of the support can be dug by a dredger.
The piles are also driven in the same way. The steel reinforcement frame is constructed onshore and then lowered into the underwater excavation with a crane. For concreting under water, the designated place is dried with the help of caissons, or a special cement, which quickly hardens under water, is used.
The support rising on an underwater foundation must have an ice-axe shape facing against the river flow. Tall pylons can be added to the supports to support the main (carrying) cables in suspension bridges.
Span construction
Techniques for constructing spans depend on the shapes of the bridges. Lift cranes, mobile scaffolding are used. Sometimes, they use pushing devices for launching the bridge spans which include a supporting beam, skids, a sliding track fixed to the bridge pier by the pier superstructure, lifting hydraulic jacks and power pushing hydraulic cylinders, and overloading tables with lifting hydraulic jacks. In other cases, the main truss of the bridge is built onshore, loaded onto barges which are transported to the ready supports of the future bridge, and installed in its allotted place using hoisting devices. For arched and vaulted bridges, scaffolding, bracing system, temporary structures are installed and dismantled upon completion of the bridge.
At the construction sites near the bridges under construction there are work camps and even whole factories for the production of individual structures, large elements and bridge blocks, transported by different modes of transport. Installation of metal structures on site is carried out by welding, riveting, screw connections (bolts). Structures made of metal require protection against corrosion.
Common, cost-effective and quickly erected are prestressed reinforced concrete bridges. They can be built either staggered, jet or padded.
Hanging and cable-stayed bridges are constructed with ropes or struts. For suspension bridges, the ropes consist of strands that are installed separately and then assembled at the ends.
The load on the cables is distributed evenly.