Experimental Study On Fatigue Performance Of Reinforced Concrete Slab Under Fixed Load

The fatigue failure of reinforced concrete bridge deck refers to the sudden failure when the stress does not reach the strength limit of the material or even below the yield strength under repeated traffic load.The process of fatigue damage can also be understood as the consumption process of the inherent life of the material.Because fatigue failure belongs to brittle failure,there is no symptom before it occurs,which leads collapse of continuous bridges and disastrous casualties.Therefore,the research on fatigue performance of reinforced concrete deck is particularly important.In this paper,two specimens of reinforced concrete slabs with different upper steel bar diameters are made to measure the relationship among the strain of steel bar,the strain of concrete and the central deflection with load,and to observe the difference of the interface between the two specimens after failure,and to study the influence of the upper structural rib on the punching performance of the reinforced concrete slab.On this basis,by making three reinforced concrete slab members of the same material and curing conditions,the changing rules of the crack formation,width,depth and so on with the fatigue loading times were observed.The trend of the deflection of the steel bar and the concrete and the central deflection with load record the rebar,concrete and central deflection with load trends.On this basis,I analyze the trend of residual displacement,residual strain and stiffness reduction coefficient of plate specimen with fatigue load times.The main conclusions are the followings:1)The punching test of reinforced concrete slabs with the same curing conditions and different upper steel bar diameter,the failure load and the distribution of the bottom cracks of the slabs are compared when the two slabs are subjected to punching failure,the shape and angle of spalling loose concrete,the stress-strain relation of steel bar,the stress-strain relation of concrete,the stress-central deflection relation,the stress-upper slab displacement relation,etc.The main conclusions are followings:the punching shear strength of plate specimens increased slightly after the upper layer steel bar was changed from 10mm HPB300 to 12mm HRB400.The stress-strain relationship,stress-strain relationship and stress-deflection relationship of concrete have little effect on the stress-strain relationship under the loading plate.The strain of H-12-1 concrete is obviously smaller than that of H-10-1 concrete under the same load at 200mm from the loading center.The strain of H-12-1 steel bar is obviously larger than that of H-10-1 concrete under the same load at 260mm from the center.2)Three reinforced concrete slab components with identical curing conditions are tested by using S = 0.55,0.66,0.75,0.84,and 1 loading levels.The main conclusions are drawn:When different from the punching failure,the steel bar at the loading center does not reach or just reach the yield strength,and no fracture occurs under the fatigue test.The angle between the cone formed by fatigue failure and the neutral layer is about 60° than that of the punching cone formed at about 45 ° when it is damaged by punching failure,and the cracks mostly form in the previous 10,000 fatigue loads.In the later loading,the development of cracks is mainly manifested with the development of width and depth.The crack width and depth changed greatly during the first 30,000 times of fatigue loading and then tended to be stable until the specimen burst again before failure.Under the same stress level,the stiffness coefficient of the member decreases with the increase of fatigue times,but when the stress level increases,the stiffness influence coefficient increases slightly and then decreases.