Fatigue Test Of U-Shape Beams Under Urban Rail Traffic Load

Along with the promotion and application of the urban rail transit system in China, viaduct, which is one of the main structure has emerged in a variety of development. As a new viaduct structure, U-shape beam has many advantages, including security, economic, aesthetic and noise canceling. So it is gradually replacing the existing structure, and becoming the popular structure in the rail transit system, especially in the urban.In recent years, there are many preliminary studies on U-shape beam in China. Most of these researches focused on the structural characteristics, bending, torsion, deformation, crack and other properties under static loads. But there are few researches about the dynamics or fatigue behaviors of it. Therefore, according to the results of the fatigue test of 30m pretressed concrete U-shape beam in Chongqing rail transit system, in this paper, we conducted a study on fatigue behavior of U-shape beam under the urban rail traffic load, and have some preliminary conclusions.Aiming at the transverse fatigue damage, the repeated loading experiment has carried out for 6 million times on the test beam. Load system simulates the location of the train wheels. After a certain numbers of load cycles, test the beam's space deformation, concrete and steel's strain and crack under the same static load. After 6 million times repeated loading, we test the beam's bending, cracking and ultimate strength, and compare with the beam which is not being loaded before.Experimental results show that prestressed concrete U-shape beam have a good anti-fatigue properties. After 6 million times repeated loading, no transverse crack was found in the beam. The deflection, concrete and steel's strain and cracks are all increasing with the number of repeated loading increased. Moreover, there are rapid growing in the initial stages, later becoming more stable, its developmental curve similar as concrete's S-N curve under bending repeated loading. After 6 million times repeated loading, the beam's bending, cracking and ultimate strength has some attenuation, but still suffices their using and designing requirements.