Research On Initial Geometric Imperfections Model Of Cold-formed Steel Omega Column Based On 3D-DIC

At present,the lightweight cold-formed thin-walled steel frame structure system composed of open cross-sections and plug-in nodes(the system focuses on quick installation)is being applied on a large scale in multi-layer and high-rise shelf structures in the field of logistics and storage.At the same time,the high load-bearing cold-formed thin-walled steel frame structure system constructed with combined sections and web bolted nodes is being studied and applied to multi-storey houses.However,cold-formed thin-walled members are sensitive to imperfections and are prone to section buckling.It brings great difficulties to the analysis of the mechanical behavior of this kind of structure.Aiming at the cold-formed steel ohmic column,this paper constructs its initial geometric imperfections model through experiments and theoretical analysis.First,this paper uses a 3D-DIC non-contact three-dimensional binocular optical measurement system to measure the outer surface morphology of 44 ohmic columns with different cross-sections and different lengths.The one-dimensional imperfections spectrum method is the core to express the initial geometric imperfections of the ohmic column.A linear combination of 12 pure global,distortion,and local buckling modes,using constrained finite strip method(c FSM),iterative closest point algorithm(ICP),genetic algorithm as tools,using principal component analysis,factor analysis,regression analysis and other methods The combined method is to quantitatively analyze the relationship between the amplitude of the same sine component in the amplitude spectrum and the change of the cross-sectional parameters,and build the initial geometric imperfections model of the cold-formed steel ohmic column.The main conclusions are as follows:(1)Establish a set of new cold-formed steel ohmic column initial geometric imperfections measurement method based on 3D-DIC non-contact three-dimensional binocular optical measurement system,combining ICP algorithm,cross-section extraction,c FSM algorithm and crosssection fitting method to extract ohms The amplitude of each pure buckling mode in the initial geometric imperfections of the column.At the same time,this method can be extended to the measurement of the initial geometric imperfections of other shapes of cold-formed steel columns with complex cross-sections,providing a new idea and a new idea for the subsequent measurement of the initial geometric imperfections of complex cross-section columns.A relatively complete and systematic imperfection extraction program.(2)The initial geometric imperfections of the cold-formed steel ohmic column can be expressed as a linear combination of the third-order pure global buckling mode,the first five-order pure distortion buckling mode,and the first four-order pure local buckling mode.(3)In the initial geometric imperfection composition of the ohmic column,the pure distortion buckling mode accounts for the largest proportion,and the first order pure distortion buckling mode accounts for the largest proportion of the pure distortion buckling modes.The overall distribution is large at both ends and small in the middle.The “concave” distribution reflects the tendency of excessive extensibility in the end openings of the ohmic column;the first-order pure buckling mode in the pure overall buckling mode accounts for a relatively large proportion,and shows a monotonically increasing trend along the length of the column,reflecting the existence of the column The initial imperfections of bending and torsion in the overall direction;the difference in the proportion of each order of pure buckling modes in the pure local buckling modes is small.(4)Different specifications of ohmic columns have the same distribution trend for the amplitude spectrum of the same pure buckling mode after discrete Fourier transform,the difference is that the amplitude of the corresponding sine component is different.Except for the first sine component,the overall amplitude spectrum shows a decreasing exponential function distribution.The peak amplitude of the sine component is on the second sine component.At the same time,there are obvious differences in the amplitude of adjacent sine components in the spectrum.For the amplitude spectrum of the amplitude spectrum of each pure buckling mode after discrete Fourier transform,the amplitude of the low-frequency sine component is large,which determines the overall trend and amplitude of the original imperfection amplitude wave,and the amplitude of the high-frequency sine component is small,It reflects the fluctuation trend of adjacent cross-sections in the original imperfection amplitude wave,but the distance between two adjacent cross-sections taken in the actual component is very small,and the fluctuation is not obvious.Therefore,the high-frequency sine component can be ignored,and the low-frequency sine component is sufficient to describe the original Imperfection distribution.(5)Extract the common factors of the cross-section parameters,and use the method of multiple linear regression to construct a multiple linear regression model of the amplitude of the low-order sinusoidal component and the common factor in the spectrum after the amplitude of each pure buckling mode is subjected to the discrete Fourier transform.Furthermore,the initial geometric imperfection model of the cold-formed steel ohmic column related to the parameters of the column is established.At the same time,it is compared and verified,and the results prove that the model can better reflect the initial geometric imperfections of the ohmic column.