Research On Fatigue Behavior Of Bi-prestressed Concrete Beam

Bi-prestressed concrete structure in which tension area could be made to bear pre-compressive stress and compression area could be made to bear initial tensile stress is a new type of prestressed concrete structure. Compared with common prestressed structure, Bi-prestressed concrete structure exist several advantages such as reducing beam height, increasing span of bridge and enhancing bearing capacity. Bi-prestressed concrete structure can be widely used in urban bridge and big span bridge.Many researches are made on fatigue behavior of reinforced concrete and prestressed concrete, however none of the research is about Bi-prestressed concrete. It is important to do research on fatigue behavior of Bi-prestressed concrete for the extensive use of this new type structure. In this paper, fatigue load and static load experiments have been done and the bearing capacity, deflection, crack and strain of Bi-prestressed concrete beam have been analyzed through the experiments.It is shown that the anti-fatigue behavior of Bi-prestressed concrete beam and the anchorage system are good enough to meet the needs of engineering. After two million circles of fatigue load, bearing capacity of the beam is decline by 3 percent and the curve of load versus strain of pre-stressed bar appears liner. The crack resistance and rigidity of the beam descend through fatigue load. The crack load of L-1 is 30 percent lower than L-2, which also has thicker cracks. The lower anchor bar and the notch are the weakness of the beam.The calculation of deflection of Bi-prestressed concrete beam under fatigue load is made based on the related theory and fatigue experiments. In the results, it is indicated that using reducing coefficient of elastic modulus of concrete to consider the influences of fatigue load is feasible. The results of research afford references to check the deflection of Bi-prestressed concrete beam.