Experimental And Theoretical Research On Performance Of Axially Specially Shaped Columns Confined By Stirrups

In recent years reinforced concrete (RC) frame structure with specially-shaped columns has been widely applied in housing. At present, the nonlinear analysis on the loading process and seismic behavior of specially shaped columns are achieved based on computer software, the analysis accuracy depends mainly on the rationality of the analytical and material model. Many models for concrete confined by stirrups applied in nonlinear analysis based on the experiments of rectangular columns and circular columns, but the confinement effect of stirrups on core concrete is different from the rectangular columns and circular columns. In the paper, based on the tests of specially shaped columns under axial load the strength and deformation performance of confined concrete were studied, the stress-strain cure constitutive model equation of confined concrete was presented to give reference for the nonlinear analysis on the loading process and seismic behavior of specially shaped columns and structure.Based on the tests of specially shaped columns under axial load, the relationship between strain ductility factor of specially shaped columns and stirrup characteristic values was analyzed; the effects of stirrup characteristic values on confined concrete strength and peak strain were alsoanalyzed. To cross section columns, L-shaped columns and T-shaped columns, the stirrups of which are distributes according to JGJ 149-2006"Technical specification for concrete structures with specially shaped columns", the results show that the strain ductility factors are 1.2~1.8, 1.2~1.5,1.2~1.6 respectively; the confined concrete compressive strengths increase 8%~43%, 5%~19%,10%~37% to plain concrete respectively, the confined concrete peak strain increase 25%~195%, 13%~72%, 22%~104% to plain concrete respectively.The performance of axially loaded specially shaped columns confined with stirrups was studied by ANSYS soft. The calculated results are much coincided with the experimental results, which proves the analytical model be more accurate and more proper. The mechanical law of confined concrete was further analyzed. And on that basis, the effects of stirrup characteristic values, stirrup spacing and arrangement on the transversal restraint stress of stirrups were analyzed. The equation was presented between the transversal restraint stress of stirrups and stirrup characteristic values, the stirrup effective restraint coefficient.The relationship between compressive strength and peak strain of confined concrete and stirrup characteristic values, stirrup effective restraint coefficient were analyzed. The results show that, to cross section columns, compressive strength and pek strain of confined concrete have respectively a linear relationship and a noliner relationship with the product of stirrup characteristic values and stirrup effective restraint coefficient; and to L-shaped columns and T-shaped columns, compressive strength and peak strain have respectively a nonlinear relationship with the product of stirrup characteristic values and stirrup effective restraint coefficient. Taking the restraint effect of stirrups account, the calculation formula of axially loaded ultimate bearing capacity were presented for short specially shaped columns, which are safe when compared with experimental results and may be used to analyze the ultimate bearing capacity of axially loaded short specially shaped confined with stirrups.Taking the restraint effect of stirrups account, the calculation formula of axially loaded ultimate bearing capacity were presented for short specially shaped columns, which are safe when compared with experimental results and may be used to analyze the ultimate bearing capacity of axially loaded short specially shaped confined with stirrups.