Behavior evolution and deformation prediction of RC beams with double openings under fatigue loading

Abstract

In the design of complex high-speed railway platforms, bridges, and other transport hub structures, openings need to be made in the reinforced concrete (RC) beam web due to the laying of pipeline lines. The performance degradation caused by the openings is a concern for the RC beam under fatigue load. To study the fatigue performance of RC beams with double openings, six RC beams with double openings were designed, with the load level ratio, location of loading points, and number of fatigue cycles as changing parameters. Fatigue tests were carried out under repeated loads. The stress state and failure mode of RC beams with double openings under fatigue load were studied, and the influence of various parameters on the fatigue performance of beams with double openings was discussed. The deformation compatibility model of opening and mid-span deformation was proposed, and the deformation evolution law of double-opening RC beam is analyzed based on the model. The results indicate that under cyclic loading, the fatigue failure modes of double opening RC beams are inclined cracks in the upper and lower beams of the opening and cracks in the corner of the opening. The specimen with a maximum load limit of 0.7Pu and a load position acting on the middle of the opening undergoes fatigue failure. The double opening RC beam has a fatigue life of at least 410000 cycles under a load level of 0.5Pu. After the fatigue test, the remaining ultimate bearing capacity, flexural stiffness, and ductility of the RC beams deteriorate with the increase of load level. The residual performance of the specimen after fatigue is even worse when the load is located in the middle of the opening. Increasing the fatigue cycle to 410000 cycles has an impact on the remaining ultimate bending moment of about 7% and the remaining flexural stiffness and ductility degrade by about 25%. Based on existing research results, a fatigue deformation prediction method for RC beams with double openings was proposed, with an error of less than 7%.