The Study On Earthquake Resistance Of Corroded Steel Beam-to-column Connections Under Neutral Salt Spray Corrosion Environment

The steel structure with its mechanical and economic performance and other advantages,is widely used in large bridges and offshore oil platforms,industrial and civil construction field,its good ductility seismic design is preferred.However,a lot of long-term steel structures under corrosive environment,it is difficult to avoid corrosion by protective measures.Under the condition of neutral salt spray,the surface of steel member is easy to form non-uniform corrosion.The existence of non-uniform corrosion not only reduces the cross-sectional area of the component,cut down the bearing capacity of the component,but also changes the local stress state on the surface of the steel,causes the stress concentration,decrease the plasticity and fracture toughness of the steel,accelerates the initiation and expansion of the crack,resulting in significant degradation of the seismic performance of steel structure.In this paper,the effect of corrosion on the seismic behavior of steel structure frame beam-column joints is studied by means of experimental study,theoretical analysis and numerical simulation.The main research work and research results include:(1)Five kinds of steel structure beam-column joint specimens with different degree of corrosion were obtained by the method of accelerated corrosion test in outdoor neutral salt spray environment.The results show that the hysteresis curves of the five beams and columns are relatively full,which shows that the steel structure beams have good energy dissipation capacity.The deformation rules and failure modes of the beam-column joints are basically the same,and the faults are destroyed at the root of the flange.With the increase of the degree of corrosion,the bearing capacity,deformation capacity and energy dissipation capacity of beam-column joints are weakened,which shows that the steel structure caused by the corrosion damage of the steel structure is serious.(2)The monotonic tensile test of Q235 B steel with different corrosion ages was carried out,and the effect of pitting corrosion on the ductile fracture of steel plate was analyzed.Based on the finite element simulation method of micromechanical damage mechanics,the parameter values of different pit size calculation is carried out,the influence of pitting geometric parameters on the stress triaxiality is analyzed,the monotonic and cyclic equivalent ductile fracture criterion considering the effect of pitting damage is established.(3)Based on the obtained ductile fracture criterion,the finite element analysis software Abaqus was used to develop the corresponding subroutines usdfld,and the finite element models of different ages were established.The finite element numerical calculation are compared with the test results of rusting of steel beam column node results.The comparison results show that the finite element model established in this paper has a high precision for the analysis of the seismic performance of steel frame column joints.On the basis of the above analysis,the influence of neutral salt spray corrosion damage on the seismic behavior of corroded steel structure beam column joints is further studied.