Study On Distortional Buckling Of Cold-formed Stainless Steel Beams

Stainless steel structures have a couple of advantages,such as corrosion resistance,good appearance,eco-friendliness,heat resistance,high ductility.The high strength-to-weight ratio and high level of cold-working within cold-formed members fits well with the high material cost and obvious stress strengthening properties of stainless steel.So cold-formed stainless steel members are widely used in stainless steel structures.Stainless steel has non-linear material properties,and cold-formed stainless steel members with open sections are likely to develop sectional buckling(local and distortional buckling),so this kind of members has complex non-linear buckling behaviors.At present,the design rules on this kind of members are not well established and corresponding research is still under way at home and abroad.In this dissertation,the distortional buckling of cold-formed stainless steel beams with open sections is investigated.Four-point loading test of C section cold-formed stainless steel beam is carried out and numerical modeling and parametric analysis of C and Z section beams are carried out.The main contents of this dissertation includes:(1)Experimental study of distortional buckling of C section cold-formed stainless steel beam.The experimental specimen sections are designed using the CUFSM software to make sure that the specimens' sectional elastic distortional buckling critical stress is lower that local buckling.Lateral supports are adopted to avoid the global buckling of test specimens in the four-point loading test,and eight test specimens develop distortional buckling failure as expected.304 stainless steel material mechanical property test is carried out.High-precision imperfection measurement equipment is set up using linear guide rail,walking device and laser displacement sensor.The initial imperfection of the test specimens are measured.The material mechanical properties,imperfection,and the force,displacement and strain data are obtained through these tests.(2)Numerical simulation and parametric analysis of cold-formed stainless steel beams.The measured section size,measured material mechanical properties(polygonal constitutive relation),measured initial imperfection data are adopted to establish a fine numerical model based on ABAQUS.The simulation results and loading test data match well,so the numerical simulation method is feasible.The method of distinguishing distortional buckling point by monitoring strain of the corner region at the boundary of compression flange and web is discussed.Parametric analysis is carried out using different stainless steel material mechanical properties,different normalized distortional buckling slenderness,different sections.72 specimens are analyzed,the result of which effectively expand the experimental data.(3)Theoretical analysis of distortional buckling of cold-formed stainless steel beams.Based on the experimental and simulated data,the method of distinguishing distortional buckling point by monitoring strain of the corner region at the boundary of compression flange and web is further discussed.The effects of different material mechanical properties and different sections on the distortional buckling bearing capacity of specimens are investigated.Based on the data above and data in the related paper,the design formula suitable for the distortional buckling capacity of C and Z section cold-formed stainless steel beam is obtained with the formula of direct strength design method.The research in this dissertation makes up for the lack of experimental and theoretical research on the distortional buckling of this kind of members and provides theoretical basis for the related design and research.