Theoretical Analysis And Experimental Study On Axial Compressive Bearing Capacity Of Concrete Columns Confined With GFRP Tubes Under Soaking Condition

A combined theoretical,numerical,and experimental research on axial compressive bearing capacity of concrete columns confined with GFRP tubes(CCGFT)under soaking condition is conducted in this thesis.Based on Tsai-Hill yield criterion of orthotropic plate and the yield principle of concrete-filled steel tube,the GFRP-tube yield criterion is presented.According to the three different yield criteria(GFRP-tube yield criterion,Hoffman yield criterion,Wang Zhenming's modified Tsai-Hill yield criterion)and the limit equilibrium relationship between GFRP tube and concrete,three kinds of formulas for calculating the axial compressive bearing capacity of CCGFT columns are derived,respectively.According to the regularities of the attenuation of GFRP materials with immersion time in water immersion and seawater immersion environment,respectively,the method for calculating the axial compressive bearing capacity of CCGFT columns under soaking condition is provided.Through axial compression experiments of five groups of total ten short GFRP-tube concrete columns and thirty finite element numerical models,the accuracy of theoretical formulas is verified,and the effects of water and seawater immersion on the axial compressive properties of short CCGFT columns were analyzed.The results indicate that the three axial bearing capacity calculation formulas of CCGFT columns based on GFRP-tube yield criterion,Hoffman yield criterion and Wang Zhenming's modified Tsai-Hill yield criterion can be used to calculate the ultimate axial bearing capacity of CCGFT columns.The calculation formula can also be used to calculate the ultimate bearing capacity of CCGFT columns under water and seawater immersion,and the analytical results are confirmed the good agreement with the numerical and experimental data.The water and seawater immersion environment has an influence on the ultimate bearing capacity and deformation performance of CCGFT columns.Through the bearing capacity formula based on Wang Zhenming's improved Tsai-Hill yield criterion,the influence of three factors,including fiber laying angle,GFRP tube thickness and concrete strength on the axial compressive bearing capacity of CCGFT columns is analyzed.The results indicate the nonlinear variation of the fiber laying angle and ultimate bearing capacity.Increasing the thickness of GFRP can significantly improve the ultimate bearing capacity and deformation capacity of composite columns under axial compression.The ultimate bearing capacity of composite columns can be significantly improved with the increase of concrete strength,however the deformation ability decreased.