Mechanism And Design Method Of Reinforced Concrete Filled Square Steel Tubular Columns

Engineers began to attempt to put some reinforcement in concrete-filled steel tube for improving fire-resistant performance and solving core concrete shrinkage and creep in bottom of high-rise building.But the latest country code,Technical Specification for Soncrete-filled Steel Sube Structures(GB50936),did not considered the effect of reinforcement in load capacity calculation and did not give some designed advices about configuration of reinforcement cage.Especially,force mechanism of inner reinforcement cage to concrete-filled square steel tube,load capacity and effect of seismic performance were not researched systematically.Therefore,this thesis using experiment,FEM and theories analysis methods deeply and systematically researched axial compression,bending,eccentric compression and seismic performance of reinforced concrete-filled square steel tube.The main research works and results are as follows.(1)Finishing 36 axial compression experiments of reinforced concrete filled square steel tube.Mechanism of reinforced concrete filled square steel tube under axial compression were discussed after the process and distribution of damage process,damage mode and steel strain development were tested in the experiments.Regulation of axial compression capacity of reinforced concrete filled square steel tube to designed parameters were analyzed through acquiring load-displacement curve in axial compression.The evolution process of apparent destruction and analysis method of macroscopic mechanical curve matching were built.It is really data support to build FEM and load capacity calculation.(2)10 seismic experiments of reinforced concrete filled square steel tube were conducted.Process of apparent destruction and final destruction mode were observed,acquiring hysteretic curve of horizontal force-displacement,local strain of spiral reinforcement,longitudinal reinforcement and square steel tube.Destruction mode,strength degraded,stiffness degraded and energy dissipation capacity of spiral reinforcement,longitudinal reinforcement and concrete-filled square steel tube were analyzed to support the theoretical analysis.(3)Force mechanism of reinforced concrete filled square steel tube in axial compression,bending and compression-bending situation were appealed.Elaborate FEM were built and were verified suitable by experimental data.Combined the result of FEM and experiments,destruction process and final destruction mode were analyzed from local deformation and strain situation in micro-mechanism.Building the visualization method of spiral reinforcement confinement,spiral reinforcement and destruction mode of inner force development of longitudinal reinforcement to concrete-filled square steel tube.It is a strong support to analyzed module in the sixth chapter.(4)Using FEM extended the huge number of data analysis to axial compression,bending,eccentric compression and seismic property of reinforced concrete filled square steel tube,557 cases were finished totally.Every designed parameter were analyzed systematically to all of the mechanical index,and the key design parameter were advised in the reasonable range.Especially,the configuration of spiral reinforcement and longitudinal reinforcement to gave the designed advices in the sixth chapter.(5)Design method of reinforced concrete filled square steel tube was built.The paper built the confinement module based on the axial compression destruction and concrete longitudinal stress,and axial compression capacity calculation were came up based on the confinement module.Bending capacity calculation were built to reinforced concrete filled square steel tube based on the total section plasticity hypothesis,this load-bear formulation considered the square steel tube,contribution of concrete compression and longitudinal reinforcement and did not consider the effect of spiral reinforcement.The axial compression formulation and bending formulation from the code,Technical specification for concrete-filled steel tube structures(GB50936-2014),were modified to suit the concrete-filled square steel tube structures.The paper compared the experimental data in the paper,FEM data and experimental data in the other papers to verify the load capacity formulation proposed by the paper.The results showed that load capacity from the paper have more accuracy and less discretion,and the code did not consider the effect of reinforcement to make the results more conservation.Additionally,the paper also proposed the construction technology and ensure the configuration parameters of spiral reinforcement and longitudinal reinforcement,and the inner configuration measures of huge sectional concrete-filled square steel tube in different size situation were advised.The researches in the paper could give some guides to concrete-filled square steel tube in engineering application,and relative code and researches could modify to referred the paper in the different disasters of defensive capacity.