STRENGTH AND DUCTILITY OF RECTANGULAR HIGH-STRENGTH CONCRETE FRAME COLUMNS REINFORCED WITH HIGH-STRENGTH REBAR

摘要

The strength and ductility are the most important seismic indexes for the high strength concrete (HSC) frame columns, respectively. Firstly, in the paper, the seismic strength and ductility of these kinds of columns, which used C60 and C90 concrete and 1 420 MPa yield strength rebars, were developed systematically by 6 model tests under the low circle repeated loads in the lab. Secondly, some non-linear numerical analyses also were carried out for columns with the same parameters. Finally, an experiential formula for the ductility, which is related to both the axial compression ratio and the index of stirrup, was derived on the basic of test data and numerical analysis results. The results of both test and analysis show that the strength and ductility were related closely to the following parameters: the axial load ratio, the index and spacing of stirrups, and type and strength of the confinement and longitudinal rebars etc. The flexural behaviors of the columns can be effectively improved by mixed ultra high and normal strength steel bars for the longitudinal reinforcement, especially in the case of high axial load levels. Moreo- ver, the results were also shown that the ductility of HSC columns, which were reinforced by ultra strength stirrup rebar, was better than the one by the normal reinforcement because the high strength rebar can provide the good confinement forces for the core concrete.