Railway bridges reinforced concrete subject to variable dynamic actions due
to vehicular traffic. These actions may result in the phenomenon of fatigue of steel
and concrete structures such. In the design of reinforced concrete structures
subject to cyclic loading, in general, the fatigue is considered simply, by a
coefficient kf, called coefficient of fatigue. This coefficient majora area of steel
initially calculated to fulfill the Ultimate Limit State (ULS) in order to limit, in
operation, the variations in stresses in steel to ensure a shelf life of at least 2
million cycles. This paper presents improvements in the assumptions used by the
coefficient kf fatigue, allowing the design of longitudinal reinforcement subject to
fatigue, to superior numbers to 2 million cycles, which is proposed by EB-3/67
value, and also in order to meet the service specified in the design fatigue life. In
this case, it was necessary to propose a simplified method for estimating the
number of operating cycles, starting from a standard cycle obtained by the
maximum variation of bending moments caused by train - loaded type. The study
was conducted using as a prototype railway viaduct isostatic reinforced the
Carajás Railroad ( EFC ) concrete. Trains - type were used which currently operate
in the EFC, which correspond to train ore Loaded and Unloaded. To determine the
internal forces in the structure of a numerical model was developed in the SAP
2000 program. The fatigue life of longitudinal reinforcement were determined
starting from the Miner damage rule and the SN curves of NBR 6118. The
methodology proposed in this work allowed the scaling in longitudinal
reinforcement fatigue satisfactorily in relation to the specified design life, and the
lives that were most useful deviation from the stipulated value were 300 and 400
years.
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