| Steel structures without necessary safety precautions and construction measures are prone to suffer from corrosion due to long-term exposure to the corrosion environment,corrosion damage on the surface of steel structure causes the decrease of plasticity and fracture toughness of steel,acceralating the initiation and propogation of cracks,which no doubt has a significant effect on seismic performance of steel structures during the period of service.The seismic performance of beam-column connection is a key factor influencing the seismic performance of steel frames,corrosion damage reduces the bearing area of beam-column connection,changing the surficial morphology,which must lead to the degradation of seismic performance of beam-column connection.In this paper,the deterioration laws of seismic performances of corroded welded beam-column connections were investigated,and the effects of corrosion damage on the failure mode and hysteretic property of welded beam-column connections were analyzed,clarifying the main reason resulting in the degradation of bearing capacities,cyclic rotation capacity and energy dissipation capacities.In this paper,the main research work is as follows:(1)In view of the characteristic that welded beam-column connections are prone to fracture in the weld region,the study of surface morphology and mechanical properties degradation for butt-welded joints with different corrosion degrees were conducted firstly.Subsequently,the change trends of different geometric parameters of local corrosion pits located in weld,base metal and heat-affected zone with the degree of corrosion were analyzed,and the effects of surface corrosion damage on fracture morphology,nominal strengths and ductility of weld joint subjected to monotonic and cyclic loading were investigated.(2)The degradation mechanism of micro-ductility of corroded weld joints were studied by using numerical analysis.On this basis,the effects of pitting geometry size and pitting distribution on the fracture position,fracture mode and plastic deformation ability of weld joints were analyzed,revealing the relationship between the local triaxial stress,the growth rate of equivalent plastic strain and the pitting geometry parameters.Besides,the equivalent ductile fracture model of corroded weld joints considering pitting damage was proposed.(3)Through the quasi-static tests of welded beam-to-column joints with different corrosion degrees to study the effects of corrosion damage on the hysteretic behavior and failure mode of welded beam-column connections.The results showed that the failure modes of all corroded beam-column connection were mixed fracture mode,and the bearing capacity,stiffness,ductility and energy dissipation ability of beam-column connections degenerate with the increase of corrosion degree.(4)The effects of different corrosion damage position and corrosion damage patterns on seismic performance degradation of welded beam-column connections were investigated by utilizing numerical analyses,revealing the main causes influencing the bearing capacities,rotation capacities and energy dissipation ability of corroded welded beam-column connections,and proposing the calculation formulas of yield moment(ultimate moment),accumulated total rotation and accumulated total energy dissipation for corroded welded beam-column connections.(5)Combining the quasi-static tests and numerical analysis results of corroded welded beam-column connections,the effects of corrosion geometric characteristics on the strength,stiffness,cyclic loading-unloading criteria and damage accumulation process of beam-column connections were analyzed,proposing the the damage accumulation model and non-linear hysteretic model of the corroded welded beam-column connections. |
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