Experimental Study On Mechanical Properties Of Reinforced Concrete Double-limb Thin-walled High Piers

In order to obtain the damage morphology and mechanical properties of double-limb thin-walled piers under earthquake action,the effects of different axial compression ratio,longitudinal reinforcement ratio and volume reinforcement ratio on the seismic performance of this type of bridge pier were investigated by low cycle loading test,and the failure characteristics,hysteresis curve,displacement ductility and energy dissipation performance of the test piers were obtained.At the same time,based on the calculation model of the static elastoplastic analysis method and the slip model of the base longitudinal reinforcement,the displacement ductility and the horizontal bearing capacity of the double-limb thin-walled piers under low cycle loading are calculated.The calculation method of stiffness recovery coefficient in the plastic damage model of concrete is proposed for the first time.The finite element calculation model of the test pier is established by using ABAQUS.The test results are verified,and the effect of concrete strength,axial compression ratio,longitudinal reinforcement ratio and stirrup rate on the ductility performance of double-limb thin-walled piers is further discussed.The results of experimental and theoretical analysis show that:(1)Under the action of low cycle loading,double-limb thin-walled piers experienced three stages:elastic,elastoplastic and bending failure.The failure of the test pier in the bottom of the pier,the top of the pier and the beam is serious,and there is a significant bending failure in the bottom of the pier and the top of the pier.In the joint action of the shear and bending moment,the beam of the bridge appears the obvious "X shaped" cross crack,and the plastic hinge of the end of beam is formed.For the bending failure of the bottom of the pier,the areas with greater damage to SZ-01 and SZ-04 are basically within the range of 1/4 piers at the bottom of the pier,while SZ-02 and SZ-03 are within the range of high 1/3 piers at the bottom of the pier.With the increase of axial compression ratio of test piers,the height of horizontal cracks increases significantly.(2)The pinch effect of each test pier hysteresis loop is small,and the energy dissipation and ductility performance are better,but the stiffness is poor.The deformation ability of the test piers is better,among which the displacement ductility of the test piers is between 2.63-3.68,the change amplitude is larger,the longitudinal reinforcement ratio has a significant effect on the ductility,and the volume reinforcement ratio has little effect on the ductility.(3)The ultimate thrust bearing capacity and the ultimate displacement of the pier top are calculated and analyzed by Pushover method and the slip model of longitudinal bars.The calculated results are in good agreement with the experimental results.The established calculation method can reflect the mechanical performance of the double-limb thin-walled piers under low cyclic repeated loads.(4)The use of the cyclic loading stress strain curve of concrete to analyze the characteristic points,the value and adjustment method of the compression and tensile damage factors are optimized.Based on the analysis of the characteristic points of the stress-strain curve,the calculation method of the stiffness recovery coefficient in the plastic damage model is first proposed,and its accuracy is verified.(5)The deviation between the test results and the numerical simulation results is within a reasonable range,and the trend of the two changes is consistent.The calculation model established in this paper can reflect the mechanical properties and failure characteristics of high piers with thin-walled reinforced concrete under low cyclic repeated loading.(6)The tie beam has a significant influence on the force performance of the pier.In order to ensure the ductility performance of the pier under ground motion,the stiffness of the beam should not be too large,and it is suggested that the height ratio should not be greater than 2.5.At the same time,in order to ensure the shear failure of beams,the span height ratio of beams should not be less than 1.5.(7)The hysteretic curve of the double-limb with higher longitudinal reinforcement ratio is full and the energy dissipation is good.The ductility performance of the pier can be greatly improved by increasing the axial compression ratio,while the volume reinforcement ratio and the concrete strength have little effect on the ductility.The axial compression ratio of the pier is 7.5%,the time delay is the worst,and 10%is the best.When the longitudinal reinforcement ratio is greater than 3.36%,the increase of the longitudinal reinforcement ratio can not improve the ductility of the pier.It is suggested that the longitudinal reinforcement ratio of the double-limb thin-walled piers should not be higher than 3.0%.