Study On Deterioration Of Freeze-Thaw Cycle Of Steel-Concrete Superposed Beam Shear Connector

Due to the multiple reasons of topography and geomorphology in the northwestern part of China,the temperature difference between day and night is very large,resulting in the widespread existence of freeze-thaw cycles.The damage caused by the freeze-thaw cycle to the bridge may even exceed the damage caused by various cumulative loads,which seriously affects the durability and daily operation of the concrete building.Due to its high strength,good ductility and ease of construction,stud connectors have become the most commonly used shear connectors for laminated beam interfaces.At present,there is little research on the peg joints under the freeze-thaw cycle,and the damage of the peg joints is very serious and can not be ignored.Therefore,the stress of the stud connectors under the freeze-thaw cycle is studied.Performance is very necessary.In this paper,21 freeze-thaw tests of stud connectors were carried out to study the damage of stud connectors under different freeze-thaw cycles(0,50,100,150)and the mass loss rate of concrete for stud connectors.The dynamic elastic modulus and the compressive strength were measured.Through the push-out test of the peg connector after freezing and thawing,the time-history curve of the bearing capacity of the stud connector is obtained.The time history curve of the bearing capacity of the specimen was analyzed and studied.The calculation expression of the shear bearing capacity of the stud connector was affected by the diameter of the stud and the number of freeze-thaw cycles.The main research contents include:(1)The mass loss rate,dynamic elastic modulus and compressive strength of the stud connectors were studied with the number of freeze-thaw cycles.The damage of the stud connectors after the freeze-thaw cycle was measured.(2)After the freeze-thaw cycle,the push-out test of the stud connector was carried out.The crack damage of the stud joint and the failure mode of the test piece were measured.The typical bearing capacity time-course curve of the stud connection after freezing and thawing was obtained..The bearing capacity of the stud connectors under different peg diameters and freeze-thaw cycles was fitted.The calculation formula of the shear bearing capacity of the stud connectors was affected by the diameter of the studs and the number of freeze-thaw cycles.(3)The variation of the shear stiffness of the stud connectors with the number of freeze-thaw cycles was studied.The relationship between the stiffness decay of the stud connectors and the freeze-thaw cycles was analyzed.Based on the load slip curve of the stud connection,the variation of the shear capacity of the bolts with different diameters with the number of freeze-thaw cycles was obtained.(4)Considering the interface slip of the laminated beam,the analytical formulas of the deflection,interfacial shear force and slip of the composite beam are derived.Combined with the experimental results and analytical formulas,the composite beam is calculated under different freeze-thaw cycles.The mid-span deflection and the end slip.