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Near-surface mounted reinforcement system using fibre reinforced polymer bars has been widely considered as an accepted system for strengthening of reinforced concrete columns, particularly with respect to increasing the flexural resistance. It involves cutting grooves into the concrete cover and bonding laminates inside the grooves with fillers (either epoxy resin or cement mortar) ensuring proper bond between fibre reinforced polymer laminate and concrete to prevent premature failure (debonding of laminate). Near-surface mounting does not require extensive surface preparation and takes minimum installation time than externally bonded fibre reinforced polymer. Unlike conventional fibre reinforced polymer jacketing technology, the efficiency of near-surface mounted bars does not depend on the geometry of the column cross-section as well. Previous experimental studies indicate that strengthening using near-surface mounting increases the lateral strength capacity and energy dissipation capacity of reinforced concrete columns. However, the scope of employing a strengthening system for structural retrofits is constrained by the limitations of the material used for strengthening. The lack of adequate confinement results in reduced ductility and energy dissipation capacity for columns strengthened using near-surface mounted technique, particularly under increased loading eccentricities. Jacketing of columns using fibre reinforced polymer increases confinement; however, the efficiency was observed to be reduced at increased loading eccentricities. Similarly, the flexural capacity and drift capacity under low levels of axial load were not observed to be significantly enhanced by the use of fibre reinforced polymer jacketing. Previous studies have indicated that a combination of these two systems could provide effective behaviour for reinforced concrete columns under eccentric loading. Therefore, this research focuses on utilizing a combination of these two methods in the form of a hybrid fibre reinforced polymer reinforcing system consisting of near-surface mounted bars and fibre reinforced polymer confinement to study the structural response of strengthened reinforced concrete columns under eccentric axial compression. [ABSTRACT FROM AUTHOR]

This article describes the use of fibre reinforced polymer composites to increase the strength of an isotropic metallic cylindrical shell against elephant's foot buckling. This form of buckling occurs when a cylindrical shell structure is subjected to high internal pressure together with an axial force, such as those that may occur in tanks and silos. It is particularly relevant to tanks under seismic action. Although fibre reinforced polymer composites have been widely applied to different types of structures under several loading conditions, its use to strengthen thin steel cylindrical shells has been very limited. Here, a non-linear elasto-plastic finite element idealisation is used to explore the strengthening effect of a fibre reinforced polymer strip on a thin cylinder. The optimum size and position of the fibre reinforced polymer sheet were obtained and empirically formulated. This study has shown that the strength after repair is sensitive to minor changes in the fibre reinforced polymer parameters so that a close adherence to the optimum parameter values is very desirable. [ABSTRACT FROM AUTHOR]

Research into carbon fibre reinforced polymers (CFRP)'s application to steel as a retrofitting technique has shown very promising results for improving mechanical properties. However, the limitation of these materials in a corrosion inducing environment has generally been overlooked. In this study, the interaction of CFRP and steel in extreme weather conditions and the material characteristics in causing localised corrosion (e.g. pitting) were investigated, with the primary aim of quantifying pit depth. Pits are known to initiate fatigue cracks in steels. Steel tiles placed in direct contact with different varieties of CFRP were exposed to 5% NaCl solutions at two temperatures for different durations. The specimens were microscopically examined to find the existence of pits, their depth and density. Steel with prior grinding suffered negligible pitting, whereas the sand-blasting created distinct isolated regions where pitting was more commonly witnessed. However, the most relevant observation was that even after 6 months of exposure to the aggressive NaCl environment, whatever pitting occurred, it was found not to be overly critical in reducing the mechanical strength of the CFRP/steel bonds. [ABSTRACT FROM AUTHOR]

An efficient frame finite element (FE) is developed and applied for nonlinear analysis of reinforced concrete beams flexurally strengthened with externally bonded fibre reinforced polymer (FRP) strips/plates. The developed nonlinear model is able to capture different failure modes associated with concrete crushing and cracking, yielding of steel, FRP rupture and intermediate crack-induced debonding of FRP sheets/plates. The element is formulated using force interpolation concept and a simple approach based on application of discrete springs and linear interpolation of bond forces along the element axis is adopted to take account of shear-slip. The developed formulation and analytical tool are employed to predict the loading capacity and the load-deflection response of reinforced concrete beams strengthened with FRP and the numerically simulated responses agree well with the corresponding experimental results. The major features of this frame element are its simplicity and efficiency compared with more complex FEs which makes it a suitable tool for practical use in design-oriented parametric studies. [ABSTRACT FROM AUTHOR]