Study On Flexural Behavior Of Damaged Deck Strengthened With Ultra High Performance Concrete

Most of the existing highway concrete bridges are constructed in China, which were in accordance with the design criteria of 70, early 80, and even earlier in twentieth Century. The structure of these bridges generally appear a lot of diseases, such as concrete aging, surface damage, large deformation, cracking, significantly decreased capacity, etc.. Looking for a safe, reliable, high durability of the reinforcement method is particularly important. A method for retrofitting the top slab of the reinforced concrete box girder with UHPC has been proposed. This method depends on the material properties of the reinforced UHPC itself, shear studs, and the surface bonding between UHPC and reinforced concrete, so as to enhance the overall stiffness, ductility and bearing capacity of the reinforced structure. The use of UHPC reinforcement method can not only increase the serviceability state and durability of the reinforced concrete greatly, but also gain barely weight on the structure. More critical is that it can effectively avoid the problem of the quality and durability of the organic bonding agent, which can bring great harm to the entire structure. In this paper, we mainly do some research on the transverse flexural performance of UHPC reinforced box girder roof, and the related conclusions are as follows:(l)Through the research on the local model of the 3 full scale roof of the box girder, we analyzed its cracking strengthen and load capacity. The total stiffness is highly enhanced, the crack growth rate of the reinforced concrete is restrained as well. Before the failure, there is a superior ductility and obvious deformation, and the failure mode is in line with the expectation. The strengthening method is more obvious to the overall carrying capacity, and the waterproof property and durability of the whole structure are remarkably enhanced.(2) The stress, deflection and crack strain of the test model are analyzed by using the nonlinear finite element software Marc. It shows that The measured values of deflection and crack width of test plate under sagging moment and hogging moment are larger than those calculated by finite element method. The reason is that the pre pressing cracks in the early stage of the test plate has great influence on the total stiffness of the structure. Because of the initial imperfection and the inhomogeneity of the material, the test plate is less than the finite element calculation value. The stress distribution of the model is consistent with the actual situation. The model can accurately simulate the stress in the elastic stage and the yield stage of the reinforced concrete, and the two kinds of failure modes of the model are consistent with the actual damage.(3) The crack loading, interface failure strength, ultimate bearing capacity and maximum crack width of the test plate are analyzed by the plane section assumption, the plastic theory and the bond slip theory. The cracking load of the UHPC layer under the hogging moment, the interfacial failure load on the bonding surface of the reinforcing layer and the original structure under the sagging moment, and the failure load under two loading conditions are in good agreement with the experimental results. The assumptions are established, and the failure patterns are consistent with the expectation.(4) Based on the latest research situation at home and abroad, the formula for calculating the crack width of UHPC layer based on the bond slip theory is proposed. We use the quadratic function in order to simulate the bonding force between steel bar and UHPC more closer to the actual stress situation, and the residual stress of the section of the UHPC layer is simulated and analyzed by using three different kinds of regional attenuation function for the first time. The formula for calculating the nonlinear function of crack width is obtained. At the same time, the calculation formula of the fiber reinforced concrete crack width which is recommended in the current codes at home and abroad is selected to calculate the crack width of the test board under the action of hogging moment.