Experimental Research on Fatigue Damage of Reinforced Concrete Rectangular Beam

Abstract

In order to acquire the law of the fatigue damage development of reinforced concrete rectangular beams, the ultimate load carrying capacity of a tested beam was measured through the static loading test. The carrying capacity of the beam was then taken as the basis of loading amplitudes for the fatigue tests and the constant amplitude fatigue loading tests under different load levels were carried out for another three beams. The experimental results show that the crack in the beam is composed of the oblique crack in the bending shear section and the vertical crack in the pure bending section. The fatigue cracks are symmetrically distributed along the length direction, and the two sides are basically the same. The fatigue fracture of the test beam occurs in one main cracks located in the middle section of the span. According to the crack width, height and the number of cracks, the whole fatigue test process can be roughly divided into three stages, that is, the rapid development stage, the stable stage and the failure stage. The development of the deflection of the beam and the strain increment of the steel bar and the concrete increased significantly at the beginning of the fatigue cycle; with the increase of cycle number of fatigue load, the growth rate slowed down and entered a relatively stable stage of development; as fatigue destruction gets nearer, the speed became great again. The stiffness of the beam has a relatively large decrease at the beginning of the fatigue loading. In the middle of a longer period of time, it is basically in a linear decline phase. Before the failure, the stiffness decreases greatly. Overall, the stiffness degradation of the beam shows a more obvious monotonic decreasing “S” curve. In a word, many aspects reflect that the fatigue damage of reinforced concrete rectangular beam has obvious three stages damage law. In the early and later stages of fatigue test, the damage is developing rapidly; and in the intermediate stage of fatigue test, the damage development is relatively stable.