Study On Static And Fatigue Behavior Of Composite Structure With Steel Cantilever Widening Bent Cap

With the development of economy and society,traffic jams on old bridges occur frequently.Using steel cantilever to widen the concrete cap beam has the advantages of no need to build new piers,greatly improving the traffic capacity and wide applicability,which can provide a new idea for solving the traffic jam problem of old bridges.Because the failure mechanism of the widened structure is not clear.It is necessary to study its mechanical mechanism.In view of the fact that the bent cap bears the variable load from the bearing in the practical engineering,it is necessary to carry out the related fatigue test research to broaden the fatigue performance of the hybrid structure.First of all,five kinds of material parameters,which will affect the mechanical properties of the structure,are selected as the influencing factors to obtain 27 experimental groups by carrying out the orthogonal experimental design.And ABAQUS is used for the finite element simulation analysis.According to the results of bearing capacity analysis and stress analysis,the 14^th group of material parameter combination is selected for the model experiment.Secondly,based on the selected combination of material parameters,the static loading failure test is carried out.The test results show that:（a）The hybrid structure is still in the elastic working state in the normal use stage,and the stress of the key parts of the structure statisfy the design requirements;（b）The friction coefficient of the steel-concrete interface is 0.465according to the displacement difference between the concrete and the bottom of the steel cantilever;（c）The co MParison between the experimental results and the numerical simulation results shows that the finite element simulation can greatly reflect the changes of concrete crack development,deflection and stress at key points in the process of structural stress,which verifies the accuracy of the simulation method;（d）The failure mechanism of the structure is obtained by combining the experimental phenomena and the force transfer process of the contact surface obtained by numerical simulation.Finally,the fatigue properties of the specimens were studied.Under the action of the test load corresponding to the fatigue load model I specified in the code and the fatigue load with twice the amplitude,the structure has no surface damage,and the structural stiffness and strain behavior have no obvious changes,indicating that the structure has good anti fatigue performance;In order to study the fatigue failure performance of this kind of hybrid structure,the fatigue test is continued after the prestress is reduced.With the increase of the number of load cycles,cracks gradually appear at the root of the concrete cantilever,and the load deflection curve also changes significantly;The test results show that this kind of composite structure only affects the initial stiffness of the structure after fatigue loading,but the ultimate bearing capacity is not greatly affected.The failure forms of two different prestressed hybrid structures are co MPared.