دانلود رایگان مقاله رفتار چرخه سطح جانبی ستون بتن مسلح محصور با الیاف کربن

Abstract

Reinforced concrete (RC) columns with various strengthening systems and different conditions were tested to cyclic lateral and axial loading for the purpose of performance assessment. Tests included confinement strengthening with carbon-fibre-reinforced polymer (CFRP) sheets, longitudinal strengthening with CFRP laminates and confining CFRP jacket, longitudinal strengthening with stainless steel bars and confining CFRP jacket, tested column until reinforcing steel failure, repair and CFRP confining jacket, and longitudinal strengthening with stainless steel bars. The analysis of the tests results as to load–displacement relationship and energy dissipation led to the conclusion that the use of external longitudinal strengthening with CFRP confinement is effective for performance retrofitting and upgrading, and viable in terms of execution. The load capacity increase due to strengthening reached 36–46% with good ductile behaviour. Nonlinear numerical modelling was carried out using two approaches which represent reasonably well the global performance of the studied columns for the prediction of the ascending load–displacement relationship and the peak load values in each cycle.

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.