Strengthening Of Reinforced Concrete Columns Research Articles

Concrete Shrinkage Effect on Columns Strengthened with Concrete Jackets

Placing reinforced concrete (RC) jackets around RC columns is a common strengthening technique, particularly in seismic regions. The influence of concrete shrinkage on columns strengthened with a RC jacket has not been investigated yet. This paper presents an analytical procedure to calculate the stresses induced by shrinkage of the new concrete. A variable modulus of elasticity with time and relaxation due to creep are taken into consideration in the procedure. Finite element analysis method is used to perform parametric numerical simulations. From the results, it is found that jacket concrete shrinkage reduces the strength of composite columns. This strength reduction increases as the shrinkage strain values increase. For example, a value as low as 0,6 of monolithic behaviour was found for a normalised axial load of 0,4 and a concrete free shrinkage strain of 1600 microstrains. It is concluded that the effect of concrete shrinkage must be considered when strengthening RC columns, as it induces slip at the interface between the old and the new concrete and tensile stresses in the jacket concrete.

Flexural Strengthening of Reinforced Concrete Columns with Near-Surface-Mounted FRP or Stainless Steel

Near-surface mounted (NSM) reinforcement involves cutting grooves into a concrete cover and bonding reinforcing bars inside the grooves using an appropriate filler. A large-scale experimental program was conducted to study the behavior of reinforced concrete (RC) columns under simulated seismic loading, strengthened in flexure with different types and configurations of NSM reinforcing materials. Lateral load-versus-displacement response characteristics (peak force, drift ratios, energy dissipation, and stiffness) were compared in order to examine the role of different parameters. The parameters include carbon or glass fiber-reinforced polymers (FRP) versus stainless steel, configuration and amount of NSM reinforcement, confinement via local jacketing, and type of bonding agent (epoxy resin or mortar). The results show that NSM FRP or stainless steel reinforcement is a viable solution toward enhancing the flexural resistance of RC columns subjected to seismic loads. All types of NSM reinforcing elements reached large axial strains. Local confinement with textile-reinforced mortar jackets was effective in controlling buckling of the NSM reinforcement, thus enabling this reinforcement to reach higher strains at failure. Epoxy-based bonding agencies inside grooves were more effective than cement-based mortar bonding agents.

Shear Strengthening of Reinforced Concrete Columns Using Ferrocement Jacket

This paper describes the results of a research effort on the strengthening, by use of circular ferrocement jackets (CFJs), of square reinforced concrete (RC) columns susceptible to shear failure. Based on 1:6 scale models, 6 identical RC columns were fabricated. Two of these columns were tested under as-built conditions; the other 4 were strengthened with different numbers of layers of wire mesh before being tested. Unless failure occurred at an earlier stage, all columns were tested under cyclic lateral forces and constant axial load. From test results, it was observed that both original columns suffered shear failure at low displacement ductility. By providing CFJs over the entire length, however, the displacement ductility of the columns could be improved greatly. A method to strengthen the design of columns with inadequate shear strength by using CFJs is also proposed.