International Concrete Abstracts Portal

One strategy for the rehabilitation of existing reinforced concrete columns is to target the improvement of specific local vulnerabilities in the columns related to inadequate strength or ductility. Eight full-scale columns were tested to evaluate the performance of a rehabilitation technique for square or rectangular reinforced concrete columns using a system of discrete external steel collars. Unlike other external confinement methods such as steel jacketing and fiber-reinforced polymer (FRP) wrapping, the proposed collar system exploits the benefits of confining elements with significant flexural stiffness. The project investigates the effectiveness of steel collars for rehabilitating columns when they are loaded axially at an eccentricity from the column centroid. Parameters investigated include collar spacing, collar flexural stiffness, active confining pressure, and load eccentricity. The columns were tested under monotonically applied axial loading and exhibited both strengths and ductilities well in excess of what would be expected with conventionally reinforced columns.

This paper presents an analytical method to predict the flexural performance of reinforced concrete (RC) beams strengthened by fiber-reinforced geopolymer composites (FRGC). In addition, a parametric study was performed to determine the effect of the thickness and tensile strength of the strengthening material on the moment, ductility, and energy absorption capacity of the composite beam. The proposed model adopts sectional strip discretization and incorporates the constitutive relationship of each component material. The strengthening configurations considered in the analysis include bottom, two-sided, and three-sided jackets. Four failure conditions were simulated to account for the original failure of the RC beam and are described in terms of the steel reinforcement ratio in the range of 0.87 to 2.29%. The result showed a good agreement between the predicted and experimental values and that the proposed analytical method can be used to predict the momentcurvature response. The parametric study revealed that the change in the moment and ductility value is more sensitive in the variation of FRGC thickness than the tensile strength regardless of the jacketing configurations and failure type of the unstrengthened beam.

The axial behavior of circular reinforced concrete (RC) columns strengthened with a combined ultra-high-performance fiber-reinforced concrete (UHPFRC) and glass fiber-reinforced polymer (GFRP) jacketing technique was experimentally investigated. Thirteen base column specimens were cast, each 120 mm (4.8 in.) in diameter and 500 mm (20 in.) in height, two strengthened with a 15 mm (0.6 in.) thick UHPFRC jacket, four confined by full and intermittent strips of GFRP composites, six strengthened with a novel technique of combined UHPFRC and GFRP jacketing, and one without any external strengthening. Experimental results showed that specimens confined by the combined strengthening technique recorded average increases of 197% and 252% in load-carrying capacity and energy absorption, respectively, compared to the control column. The galvanized midlayer increased load-bearing capacity by roughly 10% on average. It was also observed that specimens confined by seven intermittent GFRP strips recorded a 17% average increase in load-carrying capacity compared to the specimen with three strips of total equal width. Finally, a previous model adopted for specimens confined by concrete jacketing was modified and verified against the results of present and previous studies.

This study investigated the seismic resistance of thin, lightly reinforced walls strengthened in the out-of-plane direction by thick jacketing. To connect the thin existing wall and thick strengthening jacket, a tee shear connector consisting of one T-shaped steel section and several dowel bars and anchor bolts was used. Cyclic tests of four jacketed wall specimens were performed under out-of-plane lateral loading. The tests showed that the strength of the strengthened walls by thick jacketing was significantly enhanced. During the initial behavior, the tee shear connector performed well, not only as the shear connector, but also as the flexural tension reinforcement. However, as concrete damage increased during repeated load cycles, bond failure occurred early in the tee shear connector under flexural tension. The flexural strengths of the strengthened walls by thick jacketing were computed based on full and partial composite action of the tee section, and the bond and shear resistances of the tee shear connector were estimated in accordance with the provisions of ACI 318-19.

Many of the existing reinforced concrete (RC) structures in Turkey built prior to 1999 have deficient design details due to their non-seismic design or construction flaws. In particular, the beam-column joints (BCJs) experience high shear forces during such events, mainly due to inadequate design detailing of transverse reinforcements as well as inadequate lap splicing. Severe damage or total collapse of structures often occurred. To enhance the performance of such deficient joint systems, several strengthening techniques such as reinforced concrete and steel jacketing, as well as fiber-reinforced polymer (FRP) wrapping, have been proposed. In this study, new shear strengthening techniques were developed using carbon fiber-reinforced polymer (CFRP) to retrofit these insufficient BCJs. The effectiveness of various CFRP wrapping methodologies was investigated experimentally. One control specimen was constructed according to provisions specified by the 1975 Turkish Building Design Code, whereas four other specimens were constructed with deficiencies observed in the practice. Moreover, three additional specimens were constructed to develop alternative shear strengthening techniques via CFRP wrapping. The quasi-static tests were carried out by applying constant axial load and reversed-cyclic lateral load at the top of the column. Comparative analysis of control and CFRP-strengthened specimens’ results showed that significant improvements in the lateral load and the energy dissipation capacities were achieved by using the proposed CFRP-strengthening techniques.