The Research About The Effect Of The Uplift In Steel-concrete Mixed Continuous Bridge

The steel-concrete continuous composite beam is such a structure that the steel beam and concrete flange plat are connected by shear resistant elements to work together. Though this kind of beam have been studied widely home and abroad, there are still many technical difficulties remained both in the design theory and practical application. In this thesis, the vertical uplift performance of the interface of continuous composite beam was systematically studied by finite element numerical simulation and theoretical calculation, especially the uplift of shear studs on the beam when subjected to symmetrical concentrated loads was mainly studied. Besides, the calculation formula of the uplift of the steel-concrete continuous composite beam in complete elasticity state when subjected to concentrated loads was put forward, and the finite element numerical simulation analysis by ANSYS was carried through as a validation of the formula. This whole thesis consists of five chapters with chapter two and three as the focal points, and chapter four being the core.In chapter one, the characteristics of composite structures and the research status of composite bridges were introduced especially the slip effect and the lift displacement effect as well as the performance of the studs on the composite bridge as the shear connector. Afterwards, the primary research purpose and content as well as the research method was expatiated that theory analysis was made about the uplift of the studs in the composite beam as well as the finite element numeric simulation being the validation of the computing formula of the uplift extracted from the theory analysis, and the distribution of the uplift force along the beam was researched based on these achievement.In chapter two, the effect of the interfacial relative slip and vertical uplift were considered simultaneously in the theoretical calculation of the composite beam for the first time., and the method used in this thesis holds more theoretical significance and practical application value compared with the old analytical method, in which the effect of vertical uplift was neglected without any distinction. And the calculation formula of the uplift per unit length of the interface of the steel-concrete continuous composite beam when subjected to concentrated loads in complete elasticity state was deduced using elastic theory. During this process, three kinds of stiffness coefficient of the studs and six boundary conditions were used, including the shear resisting stiffness coefficient of the studs both in positive bending moment area and negative bending moment area, as well as the vertical uplift resist stiffness coefficient. Based on these conditions, the solutions of the nonhomogeneous differential equation with sixth order about the axial force which the concrete roof and steel beams subjected to were derived. Since the differential equation of the uplift force had correlative relations with the equation of axial force, the solutions of differential equation about the vertical uplift force can be deduced according to the axial force solutions. And the value of the uplift that each stud subjected to when under different loads could be extracted by integrating in the range of the interval between the studs.Chapter three is the focal point of the thesis, in this chapter, the models were built with the general analysis software of ANSYS. In these models, the stud was taken with the unit of BEAM188 that coupled with the steel beam in all directions and so with the concrete in X direction. However, in the direction of X and Y, correlative equations had to be built as the constraints, and the rotation angle of the beam in space had to be controlled for better connection. The models were built both for the structures of the continuous beams under prestress and without the action of prestress.And in the structure of continuous beam under pretress, the spatial beam unit of LINK8 was chosen to simulate the steel beam strand under perstess. Since the force imposed on the steel beam was non_adhesive vitro prestress, the beam unit only connected with the ribbed stab (Solid 45) of the beam, meanwhile, the effect that the strand get through the ribbed was simulated by coupling the correlative degrees of freedom in X direction and Y direction with Z direction being along the beam. The model of the composite beam was applied with supporting constraints and symmetrical concentrated forces, and with temperature decreasing imposed on the beam strand subjected to vitro prestress to get tension press. In the end, the deflection nephograms of the whole structure of the composite beam and the studs under different loads when subjected to prestress or not in the elastic range were obtained.In chapter four, by modeling with ANSYS, the curves of the uplift along the composite beam under different loads were obtained. The differential equations about the axial force and the vertical uplift per unit length of the continuous composite beam when subjected to concentrated loads were built, and the theoretical calculation formula could be obtained by solving these equations. Aftwards, a program was compiled using the language of MATLAB to calculated the value of uplift of the continuous steel-concrete composite beam under the concentrated loads of 20 tons, 40 tons,60 tons and 80 tons, and the curves of the uplift of the studs along the beam had been drew. Through these curves, we can know that the uplift of the continuous steel-concrete composite bridge gets the maximum value at the inflection point and the end of the bridge.Comparing the value of vertical uplift of the studs extracted from the theoretical calculation formula with which derived from the ANSYS modeling analysis, a favorable anastomosis could be found between them, which provided the validation that the research method chosen in this thesis is reasonable and correct. This result could provide the uplift-resistant design of the studs with better theoretical calculation basis, as well as the effective reference for the arrangement of the studs, which means, the interval between the studs should be decreased where the value of uplift is bigger, and increased where the value is smaller, in order to make the force of the studs more even and help the studs play its role as the connector to the maximum extent, which could increase the connecting strength between the steel beam and the concrete structure and improve the ultimate the bearing capacity of the composite bridge effectively.