Experimental Evaluation of Repaired RC Columns Subjected To Biaxial Horizontal Loading and Variable Axial Load With Reinforcement Welded Steel Bars

Abstract eng:
The study of the reinforced concrete columns’ response to horizontal cyclic loads is of full importance to understand how earthquakes affect the integrity of structures, essentially those already built and especially vulnerable to this type of action, as is the case of many existing buildings on significant seismic activity zones which are not adequately prepared for that eventuality. This importance is mainly justified by that the actual behaviour of RC building columns during an earthquake is strongly related to the random characteristics of the seismic event, the building’s three-dimensional response characteristics and its structural irregularities; and finally that the biaxial bending-moment cyclic demands applied to an RC column tend to reduce its capacity and cause stiffness and strength deterioration during successive load reversals. Large number of RC columns were designed according to the practice that not taking into account the importance of plastic deformation and ductility capacity, are commonly deficient in flexural ductility, shear strength and flexural strength under strong seismic excitations. Lap slices in critical regions, premature interruption of longitudinal reinforcement and lack of lateral confinement are common practices causing such deficiencies. However, experimental research on the inelastic response of RC elements under compressive axial force and biaxial lateral cyclic bending load conditions is currently very limited. The limited research may be due to the uncertainties concerning the relation between the two orthogonal horizontal loading paths and the complexity of the experimental setup required to perform appropriate tests. Consequently, the current knowledge regarding the inelastic response of RC columns under biaxial cyclic moments still lags behind the understanding of one-dimensional (1D) cyclic bending behaviour under a compressive axial load. Recent earthquakes should motivate further studies with the objective of develop also repair and/or retrofit strategies that could be restore the original capacity of the columns and improve their behaviour when subjected to multi-axial loadings. With this aim an experimental work was conducted at the Laboratory of Earthquake and Structural Engineering – LESE to study the cyclic behaviour of eight RC columns, two of them “as built” and the six remaining damaged that were submitted to repair procedures through welding process of the longitudinal reinforcement and were subjected to uniaxial and biaxial bending combined with constant and variable axial load. The results will be presented in terms of damage evolution along the tests, shear-drift hysteretic curves and total energy dissipation and each repaired column result will be compared with the results of the original ones, deducting about the structural efficiency repair procedures adopted. From the experimental results it was observed similar results between the repaired and the original columns results in terms of initial stiffness, maximum strength and energy dissipation. Globally the repair procedures were very efficient to restore the capacity of the columns

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