Local Buckling Of Thin-walled Steel Plates Under The Effects Of Lateral Load And Stress Gradient

Concrete-filled steel tubular(CFT)columns and steel plate-concrete composite walls have excellent mechanical properties,such as high compressive strength,good seismic capacity,and large energy dissipation capacity.This is due to the effective confinement provided by the outer steel plates to the core concrete,which puts the core concrete in a triaxial compression state and significantly improves its mechanical properties.During the compression of the steel plateconcrete composite structure,the Poisson’s ratio of the core concrete increases monotonically with the load.Once it exceeds that of the steel tube,the concrete’s deformation in the transverse direction will be larger than that of the steel,resulting in internal lateral pressure that pushes the walls outward.In addition,due to factors such as load eccentricity,fabrication errors,and material defects in actual engineering,stress gradient effects often exist on the plate edges.Therefore,most of the steel plates in steel-concrete composite members are in a composite stress state of edge load with stress gradient effect and lateral pressure.In recent years,with the application of high-strength steel,the thickness of the steel plate decreases as the strength of the steel increases(the width-to-thickness ratio increases)while still satisfying the theoretical strength.This has made the local buckling of the steel plate more prominent.Local buckling of the outer steel plates may lead to early component failure due to loss of local bearing capacity and even induce overall structure failure,resulting in serious consequences.Therefore,the stability of the outer steel plate is an important prerequisite for the excellent mechanical properties of the steel plate-concrete composite structure.Based on the background mentioned above,this paper conducts a targeted study on the influence of lateral load and stress gradient effect on the local buckling performance of thinwalled steel plates.On the one hand,it lays the foundation for establishing a more complete local buckling theoretical model for steel plate-concrete composite structures.On the other hand,it also provides a reference for the study of the local stability performance of thin-walled plates that directly bear lateral loads,such as navigators,offshore oil and gas facilities,offshore wind power facilities,and thin-walled cylindrical silo structures.The main research works conducted in this paper are as follows.(1)An innovative scheme for applying lateral pressure to thin-walled steel plates and a testing device are proposed to study the local buckling behavior of steel plates under the combined effect of axial loads and lateral pressure.A constant lateral pressure load distribution is applied to the inner surface of the steel tube to directly test the local buckling performance of the hollow square steel tube under the combined action of axial loads and internal lateral pressure.The feasibility of the proposed testing method is validated through experimentation.(2)The measurement of local buckling in thin-walled plates and the identification of initial local buckling by using multiple methods to comprehensively determine local buckling in the plates are explored.Digital Image Correlation(DIC)technology is introduced to analyze the full-field distribution of longitudinal and transverse strains,as well as out-of-plane deformation of the plates.The differences in determining local buckling of steel plates using DIC-3D,DIC-2D,laser displacement sensors,and naked eye observation are discussed.Based on this,the criteria for determining local buckling of the plates are explored,which solves the problem that the local buckling cannot be identified timely by observation.(3)Based on 3D scanning reverse modeling technology,finite element numerical simulation research is conducted to analyze the influence mechanism of lateral loads on local buckling failure of thin-walled steel plates.Combined with experimental results,the impact mechanism of lateral loads on local buckling of thin-walled plates is explored,and the influences of lateral loads on the local buckling strength and ultimate bearing capacity of plates are analyzed.A comparative analysis between the 3D scanning model and the ideal finite element model is carried out to investigate the influence of initial defects,residual stress,and other factors on the numerical simulation results of the steel plates.(4)Based on the elastic stability theory and energy variational method,theoretical research on local buckling behavior of steel plates subjected to lateral loads and edge loads is conducted.According to theoretical deduction,the formulae for calculating the local buckling strength of the steel plates considering the effects of lateral load are obtained.The local buckling strength of steel plates under different boundary conditions is calculated using the theoretical model,and its accuracy is verified by experimental results.Based on the proposed theoretical model,the specific impact of lateral loads on the local buckling strength of plates is analyzed,and design recommendations for the width-to-thickness ratio limit of steel plate and plate thickness increase under different lateral loads are proposed.(5)The local buckling behavior of steel plates subjected to lateral loads and stress gradient effects is theoretically studied,and a theoretical model for local buckling of steel plates considering the influence of stress gradient effects is established.The formula for calculating the local buckling strength of the plate under the combined action of lateral loads and edge loads considering the effect of stress gradient is derived,and the accuracy of the theoretical model is verified by experimental results.Based on the proposed theoretical model,the impact of stress gradient effect on the local buckling performance of steel plates is further analyzed,and design recommendations for the width-to-thickness ratio limit of steel plates under different lateral loads and stress gradient are proposed.(6)Theoretical study on local buckling behavior of the steel plate in contact with a rigid base is conducted,considering the effects of stress gradient.Using the displacement function that satisfies both boundary conditions and deformation compatibility conditions,the formula for calculating the local buckling strength of the steel plate in the rectangular concrete-filled steel tubular subjected to bidirectional eccentric compression is derived.Moreover,the local buckling performance of the steel plate in contact with a rigid base and stiffened by binding bars is investigated while considering the effects of stress gradient.The formula for calculating the local buckling strength of the steel plate in a concrete-filled rectangular steel tubular with binding bars is derived.Local buckling analysis is carried out based on the proposed theoretical model,and design suggestions for steel plate width-to-thickness ratio limit and binding bar arrangement under different stress gradient are proposed.