Study On Shear Performance Of Stud Connectors In Steel-ECC Composite Structures After Salt Freezing Cycles

The steel-concrete composite bridge,a green and sustainable bridge structure,can fully utilize the characteristics of the high compressive strength of concrete and the high tensile strength of steel.However,China has a vast territory,and the service environment of bridge structures is complex.In some areas,bridge structures are affected by freeze-thaw and corrosion,resulting in reducing mechanical properties and shortening service life.As a key part of the steel-concrete composite bridge,stud shear connector directly affects the regular use of the bridge structure.In addition,the normal concrete works with cracks,which leads to the easy infiltration of harmful substances and accelerates the deterioration of the structure by freeze-thaw corrosion.Engineered cementitious composite(ECC)has excellent toughness and tensile deformation ability,which can effectively improve structural cracking and durability.Therefore,this paper studies the shear performance of stud connectors in the steel-ECC composite structure under a freeze-thaw corrosion environment by push-out test.The main research contents and results are as follows:(1)Concrete material performance was tested under the freeze-thaw corrosion environment.Three prism and 15 cube specimens were separately made of ECC and normal concrete with the same strength grade,and 0,50,100,150 and 200 salt freezing cycles were carried out.The test results show that as the numbers of salt freezing cycles increase,the surface damage of ECC prism specimen is lower than that of ordinary concrete prism;under the same number of salt freezing cycles,the compressive strength loss rate,dynamic elastic modulus loss rate and mass loss rate of ECC are lower than those of ordinary concrete.(2)The push-out tests of stud connectors after freeze-thaw corrosion were carried out to study the shear performance of stud connectors in the steel-ECC composite structure,whose stud diameters of 13 mm and 19 mm after 0,50,100,150 and 200 salt freezing cycles.The test results show that with the increase in the number of salt freezing cycles,the shear bearing capacity and shear stiffness of the connectors decrease as a whole;under the same number of salt freezing cycles,the shear bearing capacity and shear stiffness of the connector with the stud diameter of 19 mm are higher than that of the connector with the stud diameter of 13 mm.Among them,the failure mode of the connector with the stud diameter of 13 mm is the stud shear,while the failure mode of the connector with the stud diameter of 19 mm is the joint failure of ECC and stud.With the increase of the number of salt freezing cycles,the root of the stud has different degrees of corrosion.(3)Compare the test results with the calculation results of stud connectors’ current bearing capacity formula at home and abroad.This indicates that the existing calculation formula is unsuitable for calculating the stud connectors’ bearing capacity in the steel-ECC composite structure after the salt freezing cycle.Therefore,combined with the experimental and finite element calculation results,considering the influence of the number of salt freezing cycles,the compressive strength of ECC after salt freezing cycles,and the dynamic elastic modulus on the shear bearing capacity of the connector,the formula for calculating the shear bearing capacity of stud connectors in the steel-ECC composite structure under freeze-thaw corrosion environment is proposed by regression analysis.