The development of a network of highways and railroads in Russia and the exploitation of natural resources in Siberia and the Far North is requiring the construction of a large number of new transportation facilities and modernization of the existing transportation infrastructure. This applies in particular to bridge construction. The construction of large bridge works that can support heavy freight traffic generally requires the use of metal superstructures. The design of the superstructure is especially critical, since it is subjected to heavy dynamic and altemating loads -including loading at minus (below -50~ temperatures. The metal structures of bridges are also significantly affected by the environment -high humidity and air pollution in industrial and urban areas.The metal structures of bridges in the USSR have been made mostly of steels 15KhSND and 10KhSND, and much less often steel 16D (in rare cases, steels 14G2AFD and 152AFDps have been used in accordance with GOST 19282-73 to build urban and highway bridges and pedestrian overpasses). These low-alloy ferritic-pearlitic steels were developed at the beginning of the 1960s with allowance for the requirements on the construction and use of metal bridge structures and the capabilities of the metallurgical industry at that time. The main standard which sets forth the requirements for rolled metal products that are to be used for bridge structures is GOST 6713: "Rolled Products of Low-Alloy Structural Steel lor Bridge Construction. Specifications."Experience in modem bridge construction has brought forth several additional requirements for the quality of the rolled products. These requirements reflect the increase in the severity of the service conditions of bridges (higher train speeds and weights, harsher climatic conditions) and the fact that the designs of bridges have become more complex (with an increase in the length of the superstructures) along with the technology used to build them. For example, it is not sufficient to guarantee the resistance of the metal of superstructures to brittle fracture on the basis of impact-toughness tests of specimens with a semi-circular notch (KCU); experience in bridge construction shows that it is necessary to use specimens with an acute notch (KCV) for those tests, since the results then more accurately characterize the reliability of the material under specific service conditions. Since the metal structures of bridges also contain welded joints whose operation creates torces in the direction of the thickness of the plates, it is becoming necessary to guarantee the level of the strength and ductility characteristics in the direction of the thickness of the rolled product (Z-properties), in addition to its internal continuity.Current trends in the development of new grades of steel for welded metal structures are also imposing new requirements tor guaranteeing weldability. This applies in particular to standardization of the carbon equivalent (C e < 0.42). Ensuring this value of the carbon equivalent for the given st...
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