Research On The Static Behavior And Calculation Method Of Monosymmetric Cross-Shaped Steel Reinforced Concrete Columns

To achieve a flush face of steel reinforced concrete(SRC)beams and columns in the inner joint,a monosymmetric cross-shaped steel is appropriate to connect the steel beams inside the SRC beams.Furthermore,a monosymmetric cross-shaped steel reinforced(MCSRC)column is formed.However,very few experimental data are available for the case of MCSRC columns,and the existing research results cannot provide a technical support for practical engineering application.In view of this,the static performance and calculation method of MCSRC columns are systematically studied through experimental research,numerical simulation,and theoretical analysis.The specific contents are as follows:(1)Experimental study on compressive behavior of MCSRC columns1)Nine MCSRC stub columns were tested under axial compression,and the experimental parameters were the cross-shaped steel eccentricity ratio,concrete strength,steel ratio and volume-stirrup ratio.The failure pattern,failure mode,load-strain curves and load-deformation curves were obtained by the test.The stress mechanism and the influences of four parameters on axial compression behavior of the SRC columns were analyzed.2)Eight slender MCSRC columns were tested under eccentric compression.The failure mode,load–strain relationships,lateral deflection,as well as second-order moment were obtained and assessed in detail.The effect of the cross-shaped steel eccentricity ratio and loading eccentricity ratio on the load–lateral deflection curves for different eccentric loading directions were analyzed.(2)Investigate on theoretical model of axial load-deformation curves of MCSRC stub columnsThe confined areas of MCSRC column were divided according to scoping constraints of profile steel and stirrups.The MCSRC core column was adopted as the Research Object,and the behavior of the concrete confined by monosymmetric cross-shaped steel was emphatically focused.Furthermore,a unified stress-strain model for steel confined concrete is developed according to Mander's model.Finally,the theoretical model of load-deformation curve is established according to static balance and deformation coordination.(3)Parametric analysis on static behavior of MCSRC column using the finite element software ABAQUSA finite element model of MCSRC column was established with the software of ABAQUS.The accuracy of the proposed finite element model was verified with the experimental results.In addition,full-scale column model was adopted to used to parameter analysis.Some conclusions could be summarized as following:1)With the increase of the strength of the profile steel and the longitudinal bars,the axial capacity and deformability increased.However,it had little influence on intimal stiffness of load-deformation curves.With the strength of stirrups increasing within a certain range,the axial capacity and deformability increased.With the increase of the reinforcement ratio,the intimal stiffness and axial capacity increased slightly,and the descending section of loaddeformation curves becomes flat.With the increase of slenderness ratio,the initinal stiffness and axial capacity of composite columns decrease,but the deformation capacity of composite columns increases significantly.2)The eccentric bearing capacity and ultimate moment of the composite columns increased with the increase in strength of profile steel.With the strength of concrete and stirrups increasing,the eccentric bearing capacity of the composite columns failed in small eccentricity compression increased rapidly.The increase in strength of longitudinal bar and reinforcement ratio was obviously advantageous to the eccentric bearing capacity of the composite columns failed in large eccentricity compression.An increase in the slenderness ratio was unfavorable to the eccentric bearing capacity and ultimate moment of the composite columns,especially for columns failed in small eccentricity compression.3)The higher the axial compressive ratio,the higher the shear capacity of the composite column.Beyond a certain range,the shear capacity is reduced as well,then the increase of axial compressive ratio will have adverse affect.Increasing the shear span ratio decreases the initinal stiffness and shear capacity,but the deformation capacity increases significantly.With the increase in concrete strength,the shear capacity increased but reduced their deformation capacity.Increasing the strength of the longitudinal bar have little influence on the shear capacity and ductile deformation capacity of the columns.The increase in hoop spacing has a negative influence on the shear capacity and deformation ability of columns.(4)Calculation method for bearing capacity of MCSRC columns1)The axial capacity of MCSRC column is divided into five parts according to the division of confined concrete areas in cross-section of MCSRC column.The strengths of different confined concrete were obtained according to the proposed the strain-stress model of the confined concrete.Furthermore,a calculation method,taking the concrete confinement stress from both monosymmetric cross-shaped steel and stirrups into account,was put forward for predicting the axial capacity of MCSRC column by superimposing axial force of each part.2)First of all,the calculation method of eccentricity magnified coefficient of MCSRC column is proposed through theoretical analysis.Then,the web of the eccentric H-shaped steel is assumed to be equivalent to its flange according to the equal strength principle.Finally,a method for computing the eccentric bearing capacity of the MCSRC column was established according to the limit equilibrium theory and the plane-section assumption.3)The MCSRC column can be divided into two parts: profile steel and reinforced concrete.The shear bearing capacity of reinforced concrete was calculated based on the truss-arch model.According to superposition principle,the shear bearing capacity of the MCSRC column was obtained by superimposing the shear bearing capacity of reinforced concrete and profile steel.