Compression Behavior Of L-shaped Src Steel Column Considering Non-uniform Confinement Effect

L-shaped Steel Concrete(SRC)columns have been widely used in tall buildings because they conform to the force characteristics at the corners of tall buildings and are economically effective.In engineering structure design,the asymmetric SRC column with steel is usually equivalent to the symmetric SRC column for simplified calculation.However,the asymmetrical configuration of the steel section produces uneven constraints on the concrete,so the crack development pattern of the column,the yield mechanism of the steel section and the reinforcement,and the stress development of the concrete are different from the symmetrical configuration of the steel section.Therefore,this paper studies the mechanical properties of L-shaped steel SRC rectangular section columns under eccentric compression,and explores the development path of the uneven constraint effect caused by asymmetric steel distribution in the process of plastic development and its influence on the mechanical properties of the column.The main work is as follows:(1)Based on the theory of "arch action",the division method of non-uniform restraint zone of L-shaped SRC rectangular section column with steel is proposed;A constitutive model of constrained concrete was established considering the degradation of the constrained capacity of steel after buckling.Numerical examples show that,compared with the traditional Mander constrained concrete constitutive model,the proposed model can better simulate the descending section of the stress-strain curve,and is more suitable for the analysis of asymmetric SRC columns.(2)Conducted 6 L with rectangular cross section steel SRC column compressive mechanical properties test,and establish corresponding analysis of finite element model of the eccentricity ratio,slenderness ratio and eccentricity,strength of materials,with steel web form five parameters on the mechanical behavior of l-shaped with SRC columns is affected,the crack propagation process of the components are analyzed,sections and steel strain development process and the yield sequence,And concrete stress distribution and flow law.The results show that under the condition of ultimate bearing capacity,the L-shaped steel arrangement makes the SRC column crack first in the corner corresponding to the extremely strong and very weak restraint region,and the crack appears earlier with the increase of eccentricity.In addition,when the eccentricity is less than 0.35,the stress degradation phenomenon will not occur in the concrete at the flange of the shaped steel in the compression zone.Therefore,the load eccentricity is recommended to be controlled within 0.35.At the same time,in order to relieve stress concentration,the web eccentricity is suggested to be controlled within 0.75.The yield sequence of steel bars is as follows: the steel bars at the webs side yield first in the tensile zone,and the steel bars at the webs side yield first in the compression zone.The yield of section steel starts from the Angle of the flange in the very weak constraint region and gradually extends to the middle web.In addition,the concrete still conforms to the assumption of flat section under the action of loads at all levels,and the dividing line between steel and concrete in the tension zone and the compression zone is oblique.(3)Based on the ultimate strength theory and the measured ultimate compressive strain of concrete,the equivalent coefficient of concrete resultant force in the compression zone is modified.In addition,based on the constrained concrete constitutive proposed in this paper,the calculation formula of the bearing capacity of L-shaped steel SRC rectangular section column under eccentric load is derived.The numerical example shows that the method proposed in this paper has high accuracy in calculating the bearing capacity of L-shaped SRC column with rectangular section.