Study On Mechanical Properties Of Short Double-shaft Piers With Small Spacing In Rigid Frame Bridge

In order to meet the deformation coordination of pier beam,reduce the push stiffness of low pier and improve the ductility of pier in the rigid frame bridge with low pier due to the limitation of topography in urban interchange and ramp bridge.In this paper,a kind of small-spaced double-shaft pier is proposed.in order to explore the mechanical properties of small-spaced double-shaft pier,the static test and quasi-static test of small spacing double-shaft pier are carried out,and the failure characteristics,load-displacement curve,structural ductility and energy dissipation performance of the test pier are obtained.At the same time,the calculation method of concrete plastic damage model based on damage factor,using the fine finite element calculation model established by ABAQUS,verifies the effectiveness of the test model.On this basis,in order to obtain the optimal design scheme of the pier,the effects of filling material,axial compression ratio and leg spacing on the mechanical properties of the pier with small spacing are further discussed under the condition that the longitudinal reinforcement ratio and hoop ratio are constant.Finally,a short pier rigid frame bridge in Yunnan is selected as the research object,and the small spacing double leg pier is applied to it,and the comparative analysis under earthquake action is carried out by using Midas.It is verified that the small spacing double leg pier has good seismic performance for the short pier rigid frame bridge,which provides a reference for the application of this new type of pier in the low pier rigid frame bridge.The results of experiment and theoretical analysis show that:(1)Through the static test of model piers,it is found that the failure patterns of bridge piers show bending failure.The anti-push bearing capacity of single-leg integral piers is obviously larger than that of double-shaft piers,but its ductility and anti-push flexibility are not as good as those of double-shaft piers with small spacing.The small spacing double-shaft pier can effectively improve the displacement ductility and anti-push flexibility,and the addition of materials between the two limbs can also improve its integrity and bearing capacity,so that its mechanical properties can be significantly improved.(2)Through the quasi-static test of model pier,it is found that the difference of damage degree caused by the difference of the distance between two legs is obvious,and the bearing capacity increases with the increase of the distance between two legs,but the ductility and energy dissipation performance decrease.(3)The simulation results of the finite element model are in good agreement with the experimental results,the damage cloud map and the damage pattern of the model pier are basically the same,and the changing trend of the load-displacement curve is almost the same.the results show that the finite element model used in this paper can accurately simulate two-limb piers with small spacing.(4)The effects of design parameters such as filling material,axial compression ratio and arm spacing on the mechanical properties of small spacing double-shaft piers are analyzed by numerical simulation,and the suggested values of design parameters are obtained.(5)Combined with an engineering example of a low pier continuous rigid frame bridge,the seismic performance of the small spacing double-shaft pier proposed in this paper is compared with that of the traditional single-shaft pier.The results show that the seismic performance of short pier rigid frame bridge with small spacing double-limb piers is obviously better than that of traditional single-leg piers.