In order to improve the durability of ordinary reinforced concrete beams,a new structure of ultra-high performance concrete(UHPC)-high performance concrete(HPC)composite beam was designed,and the flexural behavior of the UHPC-HPC composite beam after chloride corrosion was tested.The decrease mechanism of flexural capacity of the composite beam after chloride erosion was studied,and the effects of erosion degree,section form and pre-damage on the flexural behavior were analyzed.The yield strength reduction coefficient,cross-sectional area reduction coefficient of steel bar and pre-damage coefficient of concrete were introduced to propose the calculation method of flexural capacity of the UHPC-HPC composite beam after corrosion,and the feasibility of the calculation method was verified.Analysis results show that the main reasons for the decrease in the flexural capacity of the beam after corrosion are the decrease in the tensile strength of steel bars,the degradation of the stiffness and toughness of the beam,and the weakening of the crack resistance effect of steel fibers.The failure of the UHPC-HPC composite beam after corrosion is characterized by one main crack near the mid-span or two main cracks near the loading point.The stress process of the UHPC-HPC composite beam is divided into three stages:linear elasticity,crack development and yield.The concrete strain of the beam section basically conforms to the assumption of plane section.The longer the erosion time is,the more the cracking load and the flexural capacity reduce.When the beam is energized and eroded rapidly for 10 d,the reductions reach 16.2％and 10.9％,respectively.The T-beam cracks earlier than the rectangular beam,the cracking load of the former is 8.1％smaller than that of the later,and the stiffness decreases faster in the later stage after corrosion.The pre-damage significantly affects the overall stiffness of the beam,the overall stiffness decreases after pre-loading,and the pre-damage coefficient after the concrete damage is 0.984.The larger the corrosion rate is,the smaller the yield strength and the cross-sectional area reduction coefficient of the steel bar are,and the change trend conforms to the quadratic parabola.The calculated flexural capacity of the UHPC-HPC composite beam after corrosion is in good agreement with the measured value,the average ratio of the two is 0.998,and the standard deviation is 0.020.10 tabs,14 figs,31 refs.
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