Research On Seismic Performance Of Steel Frame Column And Seismic Fragility Analysis Of Multi-aged Steel Frame Structure Under Offshore Atmospheric Environment

The investigations of earthquake disaster in the word show that the column damage often is more serious than other components in steel frame structure,whose safety status affect the entire structure,therefore,the study on seismic performance of steel frame colunn is of great significance.While as a metal material,steel itself has the characteristics of poor corrosion resistance.If the structure is subjected to corrosion and in highly seismic region,it understood that seismic performance after corrosion is a seirous problem to be solved.This paper has systematically studied the seismic performance of corroded steel frame columns and multi-aged steel frame structures under offshore atmospheric environment.The main research contents and conclusions of this paper are as follows(1)With the method of indoor accelerated corrosion,6 steel frame column specimens and 48 steel standard specimens were accelerated corroded under offshore atmosphere environment.Then,the tensile tests for different corrosion degree of steel specimens were performed to obtain the mechanical properties(yield strength,ultimate strength,elongation and elastic modulus)degradation law of Q235B steel with increasing of weight loss rate using the method of least squares(2)Low cyclic loading tests of 6 corroded steel frame column specimens were implemented to study the influence of different corrosion degree and loading paths on seismic performance of the columns from the hysteresis curves,skeleton curves,strength and stiffness degradation,energy dissipation perspectives.The results show that with the increase of the corrosion degree,the ultimate bearing capacity,energy dissipation capacity of the specimens decrease significantly,the strength and stiffness degradation are obvious.Loading paths have a greater influence on the development of plastic deformation and hysteretic energy dissipation of the steel columns.The results can provide theoretical support for carrying out the seismic fragility analysis of existing steel frame structure based on component(3)Based on general software ABAQUS6.12,nonliner finite element analysis were conducted on these tested columns.Compared with the test results,it can be informed that both of the two kinds of specimens have the same failure form.The hysteresis curves,skeleton curves and energy dissipation are in a good agreement,which all prove the reliability of the finite element analysis.Then,parametric analysis were carried on to investigate the influences of axial compression ratios on the columns’seismic performance.The results show that,with the increase of axial compression ratio,the ultimate bearing capacity and energy dissipation capacity decrease seriously,the degeneration of the strength and stiffness aggravate,and ductility decreases(4)Combined with the mechanical properties degradation law of corroded Q235B steel and steel corrosion rate under typical offshore atmosphere environment,4 different finite element models(20-year,30-year,40-year,50-year)of five-story steel frame structures were built.Based on incremental dynamic analysis(IDA)that the PGA and maximum story drift angle were taken as the ground motion intensity index and seismic demand index,the seismic fragility analysis of all models was conducted to obtain the seismic fragility curves of steel frame structures in different ages.The results show that with the increase of age,structural failure probabilities under different damage states are generally reduced,and the decreased amplitude increases with increasing damage.The research results could provide theoretical basis and technical support for the assessment of earthquake damage and post-disaster loss prediction.