Fatigue behavior of steel fiber reinforced concrete composite girder under high cycle negative bending action

Tensile concrete crack is a critical factor in the negative flexural region of a steel-concrete composite girder, which could influence the entire structural safety and durability dramatically. The steel fiber reinforced concrete (SFRC) has been utilized for constraining these cracks because of its good tensile performance and low cost in practice. But the practical application of SFRC is still hindered by the unclear fatigue performance of SFRC composite girder. To this end, four 3.3 m-long composite girder tests were executed for investigating the static and cyclic effects of SFRC and connector arrangement. About 3 million load cycles with a monolithic ultimate loading process were applied on each specimen. Generally, the fatigue load cycles in tests resulted in about 10-30% reduction of girders' global bending stiffness without interlay bonding, and the effect of SFRC on it was not obvious. Even though there were more fatigue load induced cracks found on SFRC slabs than on the normal concrete slabs during loading, the SFRC crack width was smaller. Moreover, the steel-concrete interlayer slip development was found to be slower in SFRC composite girders, while arranging stud connectors in groups resulted in faster slip development. In addition, the test simulation and parametric analysis with material damage plasticity models were carried out, which showed a higher longitudinal reinforcement ratio in SFRC could further reduce fatigue damage on concrete.