Study On Material Properties And Bending Bearing Capacity Of Corroded Cold-formed Thin-walled C-shaped Steel Beams

Cold-formed thin-walled steel is widely used in the construction industry,especially in the construction of light steel buildings,because of its advantages of less steel,light weight,good seismic performance and large moment of inertia.However,many light steel structures in industrial environment were often difficult to avoid corrosion through traditional protective and structural measures,and there were serious corrosion problems,which affect the safety of the structure.In this paper,the effect of corrosion on the static performance of C purlin under industrial environment for 9 years was studied from two aspects of material and component by means of experimental study,theoretical analysis and numerical simulation.The main contents are as follows:(1)Tensile tests were carried out on 50 standard specimens manufactured at the bending angle and web of C purlin,and the effects of rust degree,type and location on the mechanical properties of the material were discussed.The relationship between the fracture form,stress-strain curve and mechanical properties of steel and the degree,type and location of corrosion was studied.The constitutive model of cold-formed thin-walled steel with corrosion was established,and the calculation method of yield strength of corroded steel was put forward.On this basis,based on GEOMAGIC STUDIO reverse reconstruction of the surface morphology of steel plate corrosion,and using ABAQUS finite element software,the effects of corrosion on the mechanical properties of different steels were compared.The results show that corrosion not only changes the fracture mode of steel,but also leads to the degradation of mechanical indexes such as strength and ductility of steel.The effect of corrosion on bending angle is much higher than that on web.When the corrosion rate reaches 36%,the yield-strength ratio at the corner is 0.99,and the elongation is only 2.8%.In addition,pitting corrosion has a greater impact on ductility of steel,while overall corrosion has a greater impact on strength of steel.The effect of corrosion on cold-rolled material is higher than that on hot-rolled material.(2)Four groups of cold-formed thin-walled steel beams with rust were tested to investigate the effect of different corrosion degrees on the bearing capacity of steel beams.The relationship between failure mode,load-displacement(strain)curve,load performance index and corrosion degree of steel beams is studied.The results show that the failure modes of corroded steel beams can be roughly divided into local buckling,distorted buckling and the related buckling modes of local buckling and distorted buckling.With the increase of corrosion degree,the failure modes of specimens change from "yielding before buckling" to "direct buckling failure" and "brittle fracture".When the corrosion degree reaches about 24%,the lower flange of the steel beam will break;the reduction of material thickness caused by corrosion,the uneven rust pits on the surface and the uneven stress will reduce the bearing capacity and stiffness of the specimens,and gradually intensify with the increase of the corrosion degree.(3)The finite element model of cold-formed thin-walled steel beams with rust was established by ABAQUS finite element software,and the correctness of the model was verified by comparing with the experimental results.Based on the finite element model,the effects of different damage locations,degrees and types on the failure modes and bearing capacity of steel beams are studied.The results show that the failure modes of steel beams with different damage locations,types and degrees are different.Compared with stainless steel beams,thickness damage and rust pit damage can cause degradation of load-bearing performance.Comparing with the thickness damage of tension zone,the thickness damage of compression zone has greater influence on the bearing capacity.In addition,although rust pits have little effect on the ultimate load,they have significant effect on the yield load and buckling load.At the same time,the depth of rust pits will affect the safety reserve of the structure.