| In order to improve the comprehensive mechanical performance of traditional concrete-filled steel tube composite columns,A new type of Corrugated steel plate-polygonal concrete filled steel tubular columns(CSPCFSTs)is proposed in this paper.This component is based on the corrugated steel sheet-concrete-filled square column proposed by the research group.The structural measures improve the mechanical performance of the composite column section.The main contents are as follows:(1)The eccentric static loading test was carried out on eight CSPCFST composite columns,and the bias performance and constraint effect of the composite columns were analyzed from the bearing mechanism,failure mode,load-displacement curve,steel strain distribution characteristics and other aspects.Eccentric loading test and data analysis show that the interaction mechanism between concrete and closed multi-cavity formed by steel tube and corrugated steel plate in composite column is different from that of conventional concrete-filled steel tube column,which can form strong constraint and mechanical bite effect.The vertical force of the section is mainly borne by steel pipe and concrete,and the corrugated steel plate does not bear the vertical load.The failure modes of eccentric compression of composite column include local buckling of steel pipe on the compression side,bulging of corrugated steel plate,cracking of concrete in tensile area and crushing of concrete on the edge of compression side.When the load eccentricity increases from 0.2 to 0.8,the bearing capacity of CSPCFST composite column decreases by about 35%,and the ductility increases by about 30%.The average transverse strain of corrugated steel plate is significantly greater than the longitudinal strain.The material properties of corrugated steel plate with transverse rib can be fully used to deform energy dissipation and restrain internal concrete.(2)The numerical model of CSPCFST composite column was established by using the finite element software ABAQUS,and the failure modes and load displacement curves of the finite element model and specimens were compared.After verifying the validity of the model,systematic numerical analysis was carried out.The effects of material strength,steel thickness,slenderness ratio and corrugated steel plate specifications on the mechanical properties of composite columns were evaluated.The results show that the corrugated steel plate is mainly used to restrain the core concrete,and its vertical bearing ratio is less than 5%.As the"skeleton"of closed multi-cavity steel pipe,the increase of its thickness and strength has a great influence on the bearing capacity and bending performance of CSPCFST composite column.Based on the finite element example,the distribution pattern of transverse constraint stress of CSPCFST composite column was analyzed.The calculation method of non-uniform constraint of composite column under eccentric load was deduced theoretically,and the expression of effective lateral constraint stress of corrugated steel plate was given.(3)Based on different theories,the national codes for steel-concrete structures are introduced,and the applicability of EC4-2004,GB 50936-2014,AISC 360-16,CECS 159-2004 and other codes to the calculation of bearing capacity of new composite columns is evaluated.In view of the complex mechanical mechanism of composite column,a simplified calculation method of eccentric bearing capacity is established.Through comparison and analysis of numerical examples,the method is in good agreement with the experimental and finite element results.(4)A BP neural network model was established to predict the ultimate bearing capacity of CSPCFST composite columns.The model was based on the new composite column correlation test and finite element case database,and the network output results were in good agreement with the actual bearing capacity of specimens.The neural network model is used to study the influence of high strength material,cavity section side length,corrugated steel plate size and other parameters.Some suggestions for the design optimization of the new composite column are put forward:when f_c≥60MPa and f_y≥500MPa,the material strength should be reduced.When the strength ratio of steel concrete is 10～12,the properties of composite materials can be fully exploited.The section side length ratio of large cavity and small cavity of composite column should be 1.9～2.3.When eccentricity is less than 1.0,the length of corrugated steel plate l between 40 and 60mm is reasonable. |
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