Mechanical Behaviors Of Flat Concrete-filled Steel Stub Columns And Braced Frame Structure

The concrete-filled steel stub structure has been widely used for its excellent mechanical behaviors,good economy and construction performance.The flat concrete-filled steel stub columns refer to rectangular concrete-filled steel stub column with section aspect ratio greater than 2.Because of the same width as the wall of the building so that the column is not exposed,and the interior inside the building is elegant and convenient to arrange.However,due to the large width of the flat concrete-filled steel stub columns,the restraining effect of the wide-side steel tube on the concrete is reduced;the moment of inertia of the section along the height of the section is small,resulting in low lateral stiffness in the direction of the minor axis.Therefore,it is necessary to study the synergistic performance between steel tube and concrete and anti-side performance of flat concrete-filled steel tubular columns.In this paper,the mechanical behaviors of the flat column are studied from the aspects of axial compression,compression bending and horizontal lateral resistance.In terms of overall engineering structure,the amount of steel used in frame braced structure is smaller than that of frame steel plate shear wall structure,and the engineering cost can be reduced under the condition of meeting the design requirements such as structural lateral stiffness.Therefore,it is essential to analyze the mechanical performance of the flat column frame braced structure.The specific work is as follows:(1)Establish finite element model of the axial compression of the short column and verify the reliability of the model by comparing with the experimental results.The axial compression mechanical behaviors of the flat concrete-filled steel stub columns and square columns were compared and analyzed from the loaddisplacement curve,the contact relationship and the constraint mechanism.The influence of the steel tube thickness and the section width-to-height ratio were analyzed by parameter study.Based on the results of finite element analysis,considering the influence of section width-to-height ratio,steel ratio and strength ratio of steel tube to concrete on axial bearing capacity,a simplified calculation formula of axial bearing capacity was proposed.At the same time,a concrete section constraint model based on the aspect ratio of section was proposed.Strengthening measures were applied to the flat column with a particularly large aspect ratio,and the influence of strengthening measures on the axial compression performance was studied.The influence of the thickness layout of flat column steel tube on the compression performance was analyzed.(2)Establish finite element model of bending and verify the reliability of the model by comparing with the experimental results.The bending simulation is divided into pure bending and compression bending.Bending mechanical performance of the flat column and the square column were analyzed from the load deformation curve,the normal stress distribution of the concrete,the neutral axis position and the concrete bending moment.According to the theoretical analysis of the ultimate bending moment,the concrete peak stress amplification factor of the square section specimen was larger than that of the flat section specimen,and the plasticity development level of the square section specimen was lower than that of the flat section specimen.Through parameter study,the influence of the section aspect ratio and the flat section strengthening measures on the bending moment deflection curve is studied.The flat column and the square column under large eccentric compression and small eccentric compression were studied from load deformation curve,deformation and contact relationship.According to the section stress state of the peak point of the load,the section stress model of concrete-filled steel stub columns under compression bending was obtained.The N/Nu-M/Mu intensity relationship curve was studied by parameter study of the slenderness ratio and the aspect ratio.The N/Nu-M/Mu curve was calculated according to the concrete-filled steel tube specifications and compared with the finite element results.(3)Establish finite element model of columns under monotonic loading and verify the reliability of the model by comparing with the experimental results.The whole process analysis was studied from the load deformation curve,contact relationship and deformation.The influence of column section aspect ratio,steel tube thickness and concrete compressive strength on the lateral resistance was studied.The finite element model of concrete-filled steel stub column frame structure was established,the whole process analysis of flat column frame and square column frame were studied and the effects of axial compression ratio,column aspect ratio and column section form on the lateral resistance were studied.Steel support was added to the frame structure,and the influence of steel support on the hysteretic performance was studied.