Compressive Behavior Of FRP-confined Square RC Columns Curvilinearized With UHP-ECC

Existing research shows that FRP wrapping reinforcement is beneficial to improve the performance of circular concrete columns,Howerver,the performance of FRP-confined reinforcing square concrete columns is not as good as that of circular ones,mainly because the square section has flat edges and sharp corners.Although rounded corners can enhance the FRP confinement effectiveness of a square column,the radius of the rounded corners is limited by the column size and the concrete cover.In order to enhance the FRP confinement in the square-section column without significantly increasing the cross-sectional area,some scholars proposed a new section modification method.This method is to modify flat sides of the square section to be curvilinearization curved edge with large curvature before wrapping the FRP,this method is referred to as Section Curvilinearization.The cross-section curvilinearization method increases the cross-sectional area only to a small extent,but can greatly improve the effectiveness of the FRP confinement.However,most of the materials used in the existing research for the interlayer between the curvilinearization edge and the core square section adopt ordinary concrete or cement mortar with a strength not less than that of the core material,rather than high-strength and high-ductility cement-based materials.The material UHP-ECC is less studied.This thesis will systematically study the axial compression and eccentric compression performance of FRP-confined curvilinearization square columns using UHPECC for curvilinearized interlayers.The test parameters include rise-span ratio,number of FRP layers,interlayer concrete materials and eccentricity.The failure mode and compression performance are analyzed through experimental phenomenona and data results,and the experimental results are compared with the existing FRP confined curvilinearization column design model.The main conclusions are as follows:（1）The use of UHP-ECC in the circular arc interlayer is beneficial to improve the bearing capacity and ductility of the FRP-confined curvilinearization concrete square column,and its stress-strain curve shows good ductility after the peak value,In addition,the use of UHP-ECC in the interlayer is beneficial to suppress the lateral expansion of its core concrete.The section curvilinearization method plays a role in improving the effectiveness of FRP confinement,so the section curvilinearization method is beneficial to improve the bearing capacity and ductility of the test column.The bearing capacity of the curvilinearization column increases with the increase of the rise-span ratio and the number of FRP layers.（2）The bias test shows that the use of UHP-ECC in the interlayer is beneficial to improve the bearing capacity and deformation capacity of the curvilinearization column.At the same time,the use of the curvilinearization method,increasing the number of FRP layers and increasing the rise-span ratio can greatly improve the curvilinearized column.Bearing capacity and ductility.Due to the existence of strain gradient in the section under eccentric load,the ultimate axial strain of the compression surface of the curvilinearization section is larger than the ultimate axial strain under the axial compression of the corresponding curvilinearization size.Under eccentric load,the axial strain distribution line segment of the curvilinearization square column with UHP-ECC in the interlayer under different axial deformations is almost a straight line,indicating that its cross-section satisfies plane section assumption.（3）Using the design model of FRP confined curvilinearization rectangular concrete columns in Chinese code GB50608 2020,the predicted results are basically consistent with the test results of the test columns in this thesis.