Research On Seismic Performance Of PVA-ECC Columns With High Axial Load Ratio

The low reversed cyclic loading tests of three PVA-ECC columns were carried out, and the influence of the stirrup ratio change on the seismic performance of the columns under the high axial load ratio was studied,the seismic performance of PVA-ECC columns and the ordinary reinforced concrete columns were compared in the thesis.Three PVA-ECC columns were tested under low cyclic loading with high axial compression ratio to investigate the columns’ seismic behavior. The main test parameter is the stirrup spacing. The primary seismic performance indexes including failure mode, hysteretic performance, skeleton curve, ductility, stiffness degradation and energy dissipation capacity were discussed. The following conclusions can be made based on the results of this investigation:(a) Compared with the ordinary reinforced concrete columns, seismic performance of PVA-ECC columns were improved significantly.(b) Under high axial load, the test specimen exhibited flexure failures with better ductility, and bond splitting, spalling, of ECC as well as composite disintegration due to cyclic loading are prevented.(c) With the decrease of the stirrup spacing of PVA-ECC columns, the seismic ductility was also improved greatly. Compared with the PVA-ECC column with stirrup spacing( 90mm), the displacement ductility, the maximum drift ratio and the equivalent viscous damping ratios of the PVA-ECC columns with stirrup spacing 70 mm and 50 mm being improved by 15.6%~16.3%、17.1%~20.6% and15.6%~17.8%.(d) Minimum stirrup ratio that can satisfy certain seismic requirement on displacement ductility and drift ratio were put forward.The FEM models of the PVA-ECC columns with different stirrup spacing were established and the elastic-plastic analyses of the tested three PVA-ECC columns were carried out using FEM software-Opensees. The comparison between the FEM analysis and experimental results indicated that: the calculated hysteretic curves and skeleton curves had a good agreement with the experimental results. The seismic performance of PVA-ECC columns with higher axial load ratio and larger stirrup spacing was discussed based on the reasonable FEM models. The ductility of PVA-ECC columns was getting worse and the peak bearing capacity changed inconspicuously with the increase of axial load ratio; The ductility of PVA-ECC columns was getting worse and the peak bearing capacity was reduced with the increase of stirrup spacing, which shows that using PVA-ECC columns replacing high strength concrete columns can reduce the role of the stirrup disposition, but not meaning there can be no stirrups.