Tests And Analysis On Hysteretic Behavior Of Butt-welded Connections Under Neutral Salt Spray

Butt-welded connection was the main connection form of steel structural members,the hysteretic behavior of butt-welded connection under low cyclic loading was an important aspect to measure the seismic behavior of steel structure.However,lots of steel structures in the marine environment were difficult to avoid corrosion by means of protections and construction measures.The corrosion of steel structure butt-welded connection reduced its plasticity and fracture toughness,this would undoubtedly have a greater impact on the hysteretic behavior of the butt-welded connection.This paper was based on the corroded butt-welded connections under neutral salt spray,through experimental researches and theoretical analysis,the degradation mechanism and the law of the hysteretic behavior of the butt-welded connection were studied,the results provided technical support and theoretical basis for seismic performance evaluation of existing steel structures.The contents of this paper were as follows:(1)Through accelerated corrosion method of outdoor periodic spraying salt spray,the butt-welded connection specimens of Q235 steel were carried out for up to twelve months of rapid corrosion,the variation of corrosion mass loss rate with the corrosion time of butt-welded connection specimens was studied.The surface morphology of the base metal,the heat affected zone and the weld zone in 5 different corrosion degree butt-welded connection specimens were tested by PS50 3D topography scanner,then the test results were analyzed by mathematical statistics,and the variation law of the surface topography characteristic parameters with the corrosion time was obtained.Based on the above,the relationship between the roughness parameters,the size of thepit and the corrosion rate was established.(2)The monotonic tensile test was carried out on 12 butt-welded connection specimens by using DNS300 electronic universal testing machine,the degradation of mechanical properties of corrosion butt-welded connection in neutral salt spray environment was studied,and the relationship between the mechanical properties(yield strength,ultimate strength and elongation)and the corrosion rate was established;The low cycle loading test was carried out on 2 specimens with no corrosion and 10 corroded butt-welded connection specimens,the effects of corrosion degree on the hysteretic curves,skeleton curves,hysteretic energy dissipation and failure modes of butt-welded connections were studied.Based on the Ramberg-Osgood model,the skeleton curve model of corroded butt-welded connection was analyzed theoretically,and the relationship between the model parameters and the corrosion degree was obtained,and through the comparison of the skeleton curve and monotone curve,the effect of corrosion on the cyclic hardening characteristics of butt-welded connections was analyzed.(3)Based on the combined hardening material model in the large-scale finite element software(ABAQUS),the finite element simulation was carried out for the connection of the corrosion butt-welded connections in the low cycle loading,and the results were compared with the test results.Through the experiment and finite element analysis,a hysteretic constitutive model was proposed,which was composed of the cyclic skeleton criterion and the hysteresis criterion.The experimental results and the model calculation results were compared and analyzed,the analytical results showed that the hysteretic constitutive model proposed in this paper could simulate the hysteretic behavior of the butt-welded connections under low cyclic loading accurately.