| Research Abstract |
Fatigue characteristics of reinforced concrete beams were investigated under various corrosion environment including under fresh water and sea water and in air. Significant differences were observed in the fatigue strengths between the beams tested in water and those in air. That is, the fatigue strength at 2 ×10ィイD16ィエD1 cycles for the beams tested in water is smaller by 15〜25% compared to that in air. This value in the region of shear span/ effective depth ratio, a/d=3.5〜4.0 becomes smaller with increases in the value of a/d. The failure pattern of beams differs in air and in water and the failure pattern tends to occur as shear failure without the fatigue fracture of stirrup in water even though the same beam exhibits flexural failure in air. Shear failures may be separated into the shear compressive failure, the failure due to the fracture of tensile reinforcement at the point of intersection of the diagonal crack, and the diagonal tensile failure (related to the value of a/d, the
… More
strength of concrete and the magnitude of the applied maximum load level). The fatigue test for the beams on which the bending span only was immersed in water, was carried out. According to the flexural fatigue failure observed from these tests, the flexural failure in air was caused by the fracture of tensile reinforcement, but those in water were not only caused by the fracture tensile reinforcement but by comprehensive fatigue failure of concrete in the bending span.
For the beams subjected to repetitive load under moisture conditions, the surface treatment and strengthening method using carbon fiber sheet has the effect of an increase in fatigue life. Static and fatigue tests were also conducted on strengthened reinforced concrete beams to investigate the type of failure, and deformation and strength characteristics of the beams, with the presence/absence of anchor bolts and the kind of strengthening materials (steel or CFRP(carbon fiber reinforced plastic) plate) set as the factors. As a result, (A)the CFRP plate-bonded beams, as compared with steel plate-bonded beams, were found to have (1)smaller crack widths and crack spacings under identical loadings, (2)smaller deflection and toughness at failure, and 3)larger fatigue strength, and (B)the type of fatigue failure differs depending on the kind of plate, presence of anchor bolts and the magnitude of the applied load. Lastly, from the point of the mechanism of shear fatigue failure tested in water, the shear force component carried by concrete decreases with increases in the number of repetitive loading. Though the shear force component carried by stirrups increases with increases in the number of repetitive loading, the stirrup strain was in pre-yield range.
In addition, this report includes a prediction model of tensile creep strain of concrete based on micro pore behavior and fatigue strength of RC beams damaged by expansion due to alkali-aggregate reaction. Less
|
