Experimental Study On Fatigue Performance Of Bridge Deck Made Of UHPC With Coarse Aggregate

UHPC is a kind of fiber reinforced cement based composite.The steel fiber bridging action makes it strain hardening and multiple cracks.The material is the most dense,the matrix is dense and the pore is small,and it has super high durability.At the same time,adding coarse aggregate can effectively reduce the shrinkage and reduce the cost.Through the use of UHPC containing coarse aggregate,it can effectively solve the problem of fatigue cracking of the deck of ordinary steel-concrete composite bridge under fatigue load.Taking Nanjing five Yangtze River Bridge as the engineering background,the fatigue property of UHPC bridge deck with coarse aggregate is mainly studied.According to the differences in the characteristics of the force and the form of the structure,static load test of three scale prefabricated plates、fatigue test of four scale prefabricated plates、fatigue test of three scale prefabricated plates with initial crack、fatigue test of two joints in the positive bending moment and two full scale joints in the negative bending moment were carried out,and the fatigue life assessment was carried out by damage fracture mechanics damage theory and nCode software.1)Experimental study on fatigue performance of precast slab of Nanjing five bridge deckStudy on the effects of different curing conditions(steam curing and normal temperature curing)and stress amplitude(before and after cracking)on fatigue properties through fatigue tests of seven specimens.The result shows that the curing conditions have little effect on the fatigue performance of the bridge deck;In the actual project,it is suggested to adopt a more convenient maintenance mode at normal temperature;Compared with the static loading test,the damage of the specimens is very small after 2 million cycles,and the fatigue crack is found after 13 million cycles without crack and the stiffness decreases by 2.1%.The stiffness of the specimens with initial crack is reduced by 8.1%,it still has good fatigue performance;The stress amplitude used in the test is larger than the actual stress of the bridge deck,the test result shows that the fatigue performance of the specimens is excellent;It is feasible to apply the UHPC bridge deck to the precast plate of the five bridge of Nanjing Changjiang River.2)Experimental study on fatigue performance of wet joint of Nanjing five bridge deckStudy on the effects of the parameters of different coarse aggregate(0,15%),prestress(0MPa,5MPa)on the fatigue properties of the wet joint of the bridge deck through four specimens without considering the stiffening effect of the real bridge.The result shows that the interfacial bonding properties of the wet joints are weak and the surface is not smooth,it is easy to produce fatigue cracks in the early stage of fatigue loading,so the surface treatment should be carried out;Whether the joint material contains coarse aggregate has little effect on the overall fatigue performance of the joints;The prestress can restrain the formation and development of the cracks,and can effectively reduce the overall stiffness of the bridge panel under the fatigue load,and the 5MPa prestress can reduce the stiffness loss by 30%;It can be popularized in the bridge deck without stiffening effect.3)Fatigue life assessmentBased on damage theory of damage fracture mechanics,the fatigue life of wet joint specimens of positive bending moment is calculated by A.Alliche and D.Francois concrete damage mechanics model and nCode fatigue analysis software,and the results are compared.The result shows that the difference between the mechanical model of A.Alliche and D.Francois’ s soil damage mechanics and the calculation results of nCode fatigue analysis software is in a reasonable range,this formula can be applied to the fatigue life assessment of the UHPC bridge deck with coarse aggregate;The stress amplitude has a great influence on the fatigue life,and the fatigue life of the stress limit 7MPa is 3.4 times of the stress upper limit of 9MPa,the fatigue life of the joint in the stress upper limit 4MPa is 4.8 times of the stress upper limit 9MPa;According to the life calculation of the joint specimens on negative bending,it can be found that the 5MPa prestress can increase the fatigue life about 1.6 times,and it is suggested to apply partial prestress.Give the suggestion of parameter value.At the same time,through the parametric analysis,the 2 million fatigue failure stress amplitude is obtained,which guides the actual project.