Study on Fatigue Characteristics of Reinforced Concrete Structure under Various environment and its Application to Design

研究了钢筋混凝土梁在淡水、海水和空气等不同腐蚀环境下的疲劳特性。在水中和空气中测试的梁的疲劳强度有显著差异。也就是说，在水中测试的梁在2 * 10^6次循环时的疲劳强度比在空气中测试的梁小15 - 25%。该值在剪跨/有效比a/d=3.5 ~ 4.0区域随着a/d值的增大而减小。梁在空气和水中的破坏模式不同，即使同一梁在空气中出现弯曲破坏，其破坏模式也倾向于发生剪切破坏而不发生箍筋疲劳断裂。剪切破坏可分为剪切压缩破坏、斜裂缝交点受拉钢筋断裂破坏和斜拉破坏（与a/d值、混凝土强度和施加最大荷载水平的大小有关）。对弯曲跨仅浸在水中的梁进行了疲劳试验。从这些试验观察到的弯曲疲劳破坏来看，空气中的弯曲破坏是由受拉钢筋断裂引起的，而水中的弯曲破坏不仅是由受拉钢筋断裂引起的，而且是由弯曲跨度混凝土的压缩疲劳破坏引起的。对于在潮湿条件下承受重复载荷的梁，采用碳纤维片材表面处理和强化方法，具有提高疲劳寿命的效果。以有无地脚螺栓和加固材料（钢或CFRP（碳纤维增强塑料）板）的种类为影响因素，对钢筋混凝土加固梁进行了静力和疲劳试验，研究了梁的破坏类型、变形和强度特性。结果表明：(1)与钢板结合梁相比，CRRP板结合梁在相同荷载下具有1)较小的裂缝宽度和裂缝间距，2)较小的挠度和破坏韧性，3)较大的疲劳强度，以及(2)疲劳破坏的类型取决于板的种类，地脚螺栓的存在和施加荷载的大小。最后，从水中试验的剪切疲劳破坏机理来看，随着重复加载次数的增加，混凝土所承受的剪切力分量减小。随着重复加载次数的增加，马镫承载的剪力分量逐渐增大，但马镫应变处于预屈服范围。少

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 * 10^6 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 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 strength … More of concrete and the magnitude of the applied maximum load level). The fatigue test the beams which the bending span only was immersed in water was carried. According to the flexural fatigue failure observed from these test, the flexural failure in air was caused by the fracture of tensile reinforcement, but those in water was not only caused by the fracture of tensile reinforcement but by compressive fatigue failure of concrete in bending span.For the beams subjected to repetitive load under moisture condition the surface treatment and strengthening method using carbon fiber sheet has the effect of increasing 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) used set as the factors. As a result, (1) the CRRP plate-bounded bemas, 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 (2) 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. Less