6. Conclusions
The longitudinal strengthening of columns resulted in the increase of the load capacity – approximately 40% – although the ductility capacity decreased compared with the columns without this strengthening. Furthermore, these all columns showed a strength degrading behaviour until failure, while the column only with the confinement strengthening maintained its load capacity until rupture. Even so, failure took place for imposed displacements corresponding to drift ratios of more than 4%, considered as high displacement values for what most structures should bear. As to the performance of the materials, in all the columns the concrete crushed at an early stage of the cyclic loading and the rupture of the longitudinal reinforcing steel was observed in the subsequent cycles, except in one of the columns. The CFRP laminates, applied to one of the columns and anchored at both ends, also reached rupture at an early stage of the cyclic loading. As for the stainless steel in two of the tested columns, the strengthening bars did not reach rupture, given the highly ductile behaviour of this material. Based on the experimental results, two modelling approaches were implemented to predict the behaviour of concrete columns under axial and lateral loading with different condition and strengthening solutions with different materials. The calibration of both modelling approaches was carried out in order to simulate the complete cyclic behaviour of the columns taking into consideration not only the peak load but also the complete performance until failure. Taking into account the peak lateral load in each column, the values of both modelling results compared with the tests results vary from 1% to 10%. The numerical model using distributed inelastic frame elements shows slightly better accuracy for most columns in all behaviour relationships and parameters. The plastic-hinge approach presents globally lower values of the peak load in each cycle.
