Study On Axial Compression Performance Of Concrete Columns Strengthened With The Combination Of Prestressed Steel Strip And External Steel Frame

With the improvement of urbanization rate,China has entered a historical stage of paying attention to both construction and reinforcement.As the main load-bearing components of buildings,bridges,aqueducts and other building structures,concrete columns have the reinforcement needs to improve the bearing capacity and seismic performance.The strengthening methods of concrete columns can be roughly divided into two categories: adding load-bearing members to improve the bearing capacity and covering restraint materials to improve the ductility.Based on the composite strengthening idea of previous scholars and the experience of prestressed confined concrete,this paper combines the prestressed steel strip method with the external steel frame method,and puts forward a new method for concrete column strengthened with prestressed steel strip and external steel frame,in order to realize the improvement of bearing capacity and ductility.The strengthening method has the advantages of efficiency,reliability and mechanization.The study includes the following three aspects: 1)Axial compression performance tests of 54 concrete columns,including 38 monotonic loading tests and16 uniaxial cyclic loading tests.The influences of steel strip configuration,external steel frame configuration and initial axial compression ratio were analyzed.2)Based on the test data of 38 monotone axial compression specimens and combined with the research of previous scholars,the calculation models of peak bearing capacity and peak strain of composite strengthened concrete columns were proposed and compared with the test data.3)Using ABAQUS to simulate the axial compression performance of the strengthened columns.The work mechanism of steel strip,external steel frame and concrete was further analyzed.At the same time,the reinforcement effect of composite strengthening method on RC columns was studied.The test and analysis results show that: 1)Composite strengthening method combines the advantages of prestressed steel strip method and external steel frame method,realizing the significant improvement of both bearing capacity and ductility.2)The strengthening effect of composite strengthened columns increases with the decrease of steel strip spacing and the increase of steel strip layers.With the strength and amount of external steel frame increasing,composite strengthened columns show increasing trends in the bearing capacity and energy consumption,when the amount of steel strip is enough to prevent the global buckling of external steel frames.The initial axial compression has little effect on the mechanical property of composite strengthened columns.3)The load-displacement curves under cyclic load almost coincide with the load-displacement curves under monotonic load.Compared with the unreinforced columns,the residual deformation of the composite strengthened columns is reduced,and the degradation rate of bearing capacity and stiffness is slowed down.With the decrease of steel strip spacing,the degradation of bearing capacity of composite reinforced columns in the later stage of loading shows a decreasing trend,and the degradation speed of stiffness slows down.With the increase of the strength of the external steel frame,the bearing capacity increases.4)The calculation models of peak bearing capacity and peak strain can well predict the test results.5)The finite element analysis results can well simulate the test results.The finite element analysis shows that the composite strengthening method still has a good reinforcement effect on RC columns.