Experimental Study On Fatigue Behavior Of Steel-Concrete Composite Beams With Partial Shear Connection

Steel-concrete composite beams have been widely used in high-rise building and bridge engineering, and open up a new direction for the development large span bridges. Due to repeated loads and the vehicle dynamic load effect, the fatigue of composite beams is increasingly prominent. Specifications at home and abroad for composite beams are made of the composite beam fatigue design rules, but the terms of fatigue design is not perfect. Currently, the time of composite beams application is shorter, the fatigue problem has not yet been revealed. Therefore, furthering study on fatigue problems of composite beams is particularly significant. The main content of this dissertation includes:(1) Two welding steel-precast concrete slab composite beams and one welding steel-concrete slab composite beams have been carried out constant amplitude fatigue tests to study on their fatigue performances. These experimental researches show that:under the same degree of shear connection, steel-precast concrete slab composite beams than steel-concrete composite beams have weaker integrated stiffness, a evident downward trend with the increase of numbers of fatigue loading(2) and the degradation rate of structure stiffness accelerates in the late fatigue; The stud shear stiffness of the former degrades more quickly and the stud fatigue life is much lower than the latter; Weld defect will become the important cause of fatigue details of earlier fatigue failure, and some composite beams under dynamic loading should be strictly control the quality of weld in construction process.(3) Seven welding steel-concrete composite beams have been carried out experimental study on their fatigue performances. These experimental researches show that:Under the same degree of shear connection, the integrated stiffness of composite beams with smaller diameter studs and lesser stud spacing falls slightly, after the same numbers of cyclic fatigue loading, its static ultimate bearing capacity decreases more slowly, the composite beam deflection, the deformation of the stud slip, the integrated performance of composite beams and the performance on fatigue tests are better; Composite beams with a lower degree of shear connection, after the same numbers of fatigue loading, have a more rapid development of the mid-span deflection and the deformation of studs slip, a larger degradation of composite beam integrated stiffness and a lower residual bearing capacity, and their additional deflection deformation caused by repeated loading are also larger; Under the same degree of shear connection, composite beams bearing larger fatigue stress amplitude have a larger degradation of composite beam integrated stiffness and a lower residual bearing capacity after the same number of cyclic loading, and the mid-span deflection deformation and the stud slip deformation are also larger; Due to the cyclic fatigue loading, steel beams become brittle and steel beams are prone to fatigue fracture, but the ultimate bearing capacity do not decreased too much.(4) By discussing variation laws of the stud shear stress amplitude, the stud diameter and the regularity of the integrated stiffness degeneration of composite beams, this dissertation provides the basis for the design of composite beams in normal use stage under fatigue loading.