Study On Mechanical Behavior Of Ultra-high Performance Concrete Slab Under Concentrated Load

Ultra-high peformance concrete(UHPC)has excellent mechanical properties.Applying it to segment precast assembly technology can realize rapid and standardized construction of bridges.At present,in prefabricated bridges with joints,the research on the mechanical performance of UHPC decks under local loads is still not perfect,especially the relevant research on the punching shear performance of UHPC waffle decks.Based on this,this thesis uses 20 UHPC flat slabs and 15 UHPC waffle slabs to study the bending performance and punching resistance of the bridge deck.The main contents are as follows:(1)The influence of the steel fiber content and reinforcement ratio on the flexural capacity of 20 UHPC slabs was studied.The failure form,load deflection curve and load strain curve of each specimen are analyzed.The results show that the UHPC slab with steel fiber without reinforcement has a large bearing residual force and good ductility after reaching the ultimate load;the UHPC slab without steel fiber only has a sudden fracture after reaching the ultimate load,which has a greater brittleness.The flexural capacity will increase with the increase of steel fiber content and reinforcement ratio,but the rate of flexural capacity increases with the increase of steel fiber content,and shear failure occurs in some specimens with the increase of reinforcement ratio.Therefore,it is suggested that the steel fiber content of UHPC bridge deck is about 2%and reinforcement ratio is about 3%.The formula of bending capacity of NR-UHPC slab is proposed,the calculation value and test results are given The results show that the formula has a high accuracy.(2)In order to investigate the punching shear behavior of UHPC waffle slabs,the punching shear failure tests of 15 UHPC waffle slabs were carried out with the stiffener width,loading area and loading position as parameters.The punching capacity,bottom crack,punching failure angle and punching failure perimeter of UHPC waffle slabs are analyzed.The results show that: the punching shear capacity of UHPC waffle slab increases with the increase of stiffener width,the punching failure angle of the specimen with small loading area is larger than that of the specimen with large loading surface,and the punching failure angle of the specimen with end loading is larger than that of the specimen with middle loading.(3)Through the finite element software ABAQUS,the punching shear test of UHPC waffle slab is simulated,and the numerical model of UHPC waffle slab under different parameters is constructed.The comparison between the numerical model and the test shows that the difference between the ultimate load and deflection of the specimen is small,and the simulation results are in good agreement with the test results.(4)The applicability of the formula proposed by HAA in Germany,the technical code of fiber reinforced concrete structure in China and the technical code of active powder concrete structure to the calculation of punching shear capacity of UHPC waffle slab is discussed.The results are compared with the experimental results and simulation results.The formula proposed by HAA in Germany is relatively conservative,the deviation of Chinese fiber reinforced concrete regulations is large,and the calculated value of active powder concrete is close to the experimental value and simulation value.Finally,considering the influence of the width of stiffener on the punching capacity,the thesis puts forward the calculation formula of the punching bearing capacity of UHPC waffle slab.