Fatigue Behaviour of CFRP Bar-Reinforced Seawater Sea Sand Concrete Beams: Deformation Analysis and Prediction

The new composite application of seawater sea sand concrete (SSC) and fibre-reinforced polymer (FRP) bars had broad development prospects. In this paper, the load levels and stirrup spacing were the main research parameters. The fatigue behaviour of carbon fibre-reinforced polymer (CFRP) bar-reinforced SSC beams was studied by four-point bending tests, and the development laws of fatigue crack width and fatigue deflection were deeply discussed. Results revealed that excessive stirrup spacing might change static failure modes of CFRP bar-reinforced SSC beams, resulting in a reduction in mechanical behaviour. This paper preliminarily suggested that the maximum stirrup spacing should be 200 mm. The fatigue failure mode of CFRP bar-reinforced SSC beams in this paper was mainly shear fatigue failure. The fatigue crack width and fatigue deflection increased with the cycle number. When the cycle number reached 80% of fatigue life, the fatigue crack width increased by about 100%. When the beam specimens were close to fatigue failure, the increase in fatigue deflection ranged from 166.5% to 188.9%. Load levels had a significant impact on fatigue life, and a fatigue limit of 0.5 was proposed as a threshold. In addition, the larger the stirrup spacing, the greater the growth rate of fatigue crack width and fatigue deflection. Therefore, based on the calculation equation for the maximum crack width in the code, the influence of stirrup spacing, load levels and n/N was further considered in this paper. Considering the influence of stirrup spacing and load levels, a calculation equation for fatigue deflection was proposed. Finally, the fatigue design concept was improved, and the fatigue life was further subdivided into the fatigue life on bearing capacity and normal service.

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