The Seismic Performance Of RC Column Confined By Low-prestressed Steel Belts

A new retrofitted method that makes use of low-prestressed steel belts intransverses direction of RC columns is studied on the paper to check the effect of thenew method and the seismic performance of the retrofitted columns.Three circular columns confined by low-prestressed steel belts and two normalcolumns have been tested under axial and cyclic lateral force to investigate theeffectiveness of external low-prestressing in transverse direction of circular columns.The main parameters of the test were axial compression ratio and arrangement of s teelbelts. The main objectives of the study were to obtain information on:(a) the seismicperformance of RC columns confined by low-prestressed steel belts under high axialcompression ratio;(b) the key position of the arrangement of the steel belts.Based onthe test results, the failure mechanism, bearing capacity, hysteretic behavior, skeletoncurve and ductility were comprehensively analyzed and conclusions were as follows:(1) The retrofitted method with low-prestressed steel belts can effectivelyimprove the seismic performance of RC columns with high stirrup ratio under highaxial compression ratio, and the retrofitted effect for structures or members withhigher seismic requirement is obivious.(2) The low-prestressed steel belts strengthening can make the concrete in a stateof triaxial compression, and it can also inhibit the development of oblique cracks andeffectively improve the deformability and the seismic performance of RC columnswith high stirrup ratio.(3) The new retrofitted method studied in the paper will not increase the initialstiffness and cross-sectional dimension of retrofitted columns, so it affect the seismicaction minimally.(4) The low-prestressed steel belts can work together with stirrups, which canmake both fully participate in the work before the destruction.(5) Under the same axial compression ratio, the ductility index of confinedcolumns increases by about40%, and bearing capacity by more than15%.The FEM model of the RC columns retrofitted by low-prestressed steel beltswere established and the elastic-plastic analysis were carried out using versatile FEMsofeware-ANSYS. The comparison between the FEM analysis and experimental resultindicates that: the calculated horizontal bearing capacity and ductility index h ave a good agreement with the experimental result. The optimal arrangement of thespecimen is studied based on reasonable FEM analysis. It is suggested fullarrangement of steel belts within the scope of250mm height on the root of the columncan provide the the specimen the desired level of capacity and ductility. Thisconclusion can be referenced for the further experimental study.