Steel bridges

Steel bridges – are bridges spans and piers of which are made of steel.

Rail-road bridges are a kind of bridges constructed over water or other type of obstacles for subsequent track laying. Overpasses, viaducts and racks are also a type of railroad span structures.

Rail-road bridge consists of spans, railway track and piers, supporting the whole structure. Foundation of piers are laid on firm soil, they also can be pile-supported. Piers are the base for span structures, allowing them to move and turn under load or in case of alteration of environmental conditions. Bridge superstructure is a set of beams, trusses and bracing between them and decking.

The most common material for railway bridges is a metal; it has become popular due to its durability and reliability as well as low weight. 70% of railway bridges are made of steel. Nevertheless steel structures have their shortcomings: high steel consumption, they also require maintenance and corrosion protection.

Special requirements in terms of reliability and durability are applied to railway bridges due to high load spread on almost entire length of the bridge. The architectural design of such structure can be different.

Advantages of steel bridges

Technological effectiveness of fabrication and installation are the main advantages of steel structure for bridges. Elements of such bridges are fabricated at specially equipped plants and transported to the site for erection. Erection can be fully-mechanized, so it becomes possible to perform erection in shortest possible time.

Due to their versatility and simplicity of design steel spans, bridges can be erected in mountainous terrain, above the big rivers (dense water traffic areas included).

Reliability of steel bridges is very high. They require less money for maintenance; they also have much longer lifetime. This type of bridges is also equal in terms of reliability and durability to concrete ones.

Main elements of steel bridges

High quality of steel and its properties allow fabricating wide variety of bridge designs.

Main types of steel bridges are:

A distinctive feature of beam bridges is that only vertical pressure is put to piers, this fact facilitates greatly if piers are of bid height.
Arch bridges are strutting system. They consume less steel than beam ones. However, this imposes some constraints on the use of structures of this type, as piers should withstand heavy loads. Arch bridges are the most suitable for construction of bridges on good soils. In other cases erection of such bridge may be rather difficult especially if piers are of significant height. In most frequent cases arch bridges are constructed in urban areas. In this cases an arches of a bridge are made of solid sections. Stiffening girders are used for construction of highway bridges. In this case arch is installed in form of polygonal truss girth. Arch structures can also be continuous and cantilevered, but these types are not common.
Suspension bridges. The main elements of these bridges are: cables and chains. In some cases these elements can be land tied by means of tension bars. In order to increase the vertical stiffness, these bridges can have stiffening girders.
Combined bridges are made of beams and trusses, which are added with bottom chord in form of a flexible arch. Due to the peculiarities of combined structures, stresses of elements can be artificially adjusted. This in its turn allows reducing the cost construction. Combined bridges also include continuous girders with the top or bottom truss girth.

Bridge steel spans

Wide construction of steel bridges stared in the middle of the last century. The reason for the increased interest in this technology was the introduction of construction welding in the fabrication of bridge elements and using of bolted frictional connections instead of rivet ones for fabrication and erection. At the same time steel trusses and beam spans came into use.

The base for design of typical span structures was also established at that time: properties and design solutions, regulatory documents for construction, drawn up on the data acquired for studies of ultimate limit states, necessary grades of steel and requirements to their properties.

At he later stages has been done a design of typical steel bridge projects. Since 1995 requirements to steel span structures has been revised. In addition the reliability and durability the following properties has been added: quality of railroad (in case of railroad bridges), reduction of costs for maintenance and service works, aesthetics.

Constructionof steel bridges

Nowadays companies are tending to reduce steel consumption and make bridge erection less labor-consuming. High-strength grades of steel, welded structures, special types of connections and structures are used for this purpose.

One of the most technologically advanced elements is an orthotropic plate deck; this type is commonly used for construction of highway and city bridges. This structure is at the same time a bearing decking of road surface, chord of main beams and trusses, so there is no need o install longitudinal braces.

Preparation of detailed drawings

Detailed drawings are prepared on the basis project of a bridge. Bridge drawings are in some way different from KMD drawings for steel structures: as of today their preparation is not fully automated and thus it requires professional engineering skills.

Fabrication of bridge steel structures

The special area for fabrication of steel structures is allocated at ChSSP. This are is equipped with automated welding machines, assembly racks and other types of equipment. There is also a special group of qualified welders and QA/QC inspectors assigned to it.