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Strength and ductility of normal-strength concrete columns can be considerably improved through confinement using Carbon Fiber-Reinforced Polymers (CFRP). Low-strength concrete may be found in structures where measured strength is lower than the nominal compressive strength of concrete, old or non-code conforming structures, and low-rise housing lo...
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... The stress-strain curves of the tested columns are then presented, and the behavior of the specimens is analyzed. Subsequently, the measured stress-strain curves are compared with those obtained from some existing prediction models. Finally, a modification of the model by Harajli [10] is proposed to predict the response measured in the specimens. Fig. 6 shows the final damage state of the tested columns. In general terms, columns without CFRP confinement exhibited concrete crushing with sudden concrete spalling, followed by buckling of longitudinal bars, as shown in Figs. 6d, 6e and 6f.; stirrup fracture was not observed. Cracks formed parallel to the load application axis in both ...
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... externally-bonded CFRP confinement. The failure mode of the columns confined with CFRP was governed by ripping of the CFRP fabric, commonly in the upper two thirds of the specimen height. Upon inspection of the samples, a thin layer of concrete adhered to the CFRP fabric was observed, implying adequate bonding between concrete and the CFRP sheet. Fig. 6 shows that spalling of the concrete cover in the columns confined with CFRP was minor compared to that of the specimens without CFRP confinement; additionally, the CFRP wraps delayed core failure in the column. Fig. 6 also shows that major damage in the specimens occurred in the upper part of them, which was also observed in the ...
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... a thin layer of concrete adhered to the CFRP fabric was observed, implying adequate bonding between concrete and the CFRP sheet. Fig. 6 shows that spalling of the concrete cover in the columns confined with CFRP was minor compared to that of the specimens without CFRP confinement; additionally, the CFRP wraps delayed core failure in the column. Fig. 6 also shows that major damage in the specimens occurred in the upper part of them, which was also observed in the specimens studied by Turgay et al. [16]. These authors argued that damage is mainly concentrated over a specific branch of the column under concentric loading, due to the heterogeneous nature of the concrete. Fig. 6b shows ...
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... in the column. Fig. 6 also shows that major damage in the specimens occurred in the upper part of them, which was also observed in the specimens studied by Turgay et al. [16]. These authors argued that damage is mainly concentrated over a specific branch of the column under concentric loading, due to the heterogeneous nature of the concrete. Fig. 6b shows the confining effect of CFRP sheets on failure modes of concrete columns with longitudinal reinforcement only. The specimen with longitudinal reinforcement only (CL) exhibited cover spalling so the bars buckled and the column lost axial load carrying capacity. In the specimens with both longitudinal reinforcement and CFRP ...
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... modes of concrete columns with longitudinal reinforcement only. The specimen with longitudinal reinforcement only (CL) exhibited cover spalling so the bars buckled and the column lost axial load carrying capacity. In the specimens with both longitudinal reinforcement and CFRP confinement (CW1L and CW2L), the longitudinal bars did not buckle (see Fig. 6b) and, therefore, they continued to contribute to the axial strength of the column; in fact, f' cc for the specimens CW1L and CW2L was 27% and 54% greater than the corresponding strength of the specimen CL, respectively. The testing machine reached its maximum loading capacity (about 2000 kN) during testing of the specimens CW2LV1R2, ...
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... of the specimen CL, respectively. The testing machine reached its maximum loading capacity (about 2000 kN) during testing of the specimens CW2LV1R2, CW2LV2R1 and CW2LV2R2 and, therefore, these specimens did not reach their compression capacity. However, the CFRP fabric of the specimens exhibited some degree of horizontal tearing, as shown in Fig. 6d, 6e and ...
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... The stress-strain curves of the tested columns are then presented, and the behavior of the specimens is analyzed. Subsequently, the measured stress-strain curves are compared with those obtained from some existing prediction models. Finally, a modification of the model by Harajli [10] is proposed to predict the response measured in the specimens. Fig. 6 shows the final damage state of the tested columns. In general terms, columns without CFRP confinement exhibited concrete crushing with sudden concrete spalling, followed by buckling of longitudinal bars, as shown in Figs. 6d, 6e and 6f.; stirrup fracture was not observed. Cracks formed parallel to the load application axis in both ...
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... externally-bonded CFRP confinement. The failure mode of the columns confined with CFRP was governed by ripping of the CFRP fabric, commonly in the upper two thirds of the specimen height. Upon inspection of the samples, a thin layer of concrete adhered to the CFRP fabric was observed, implying adequate bonding between concrete and the CFRP sheet. Fig. 6 shows that spalling of the concrete cover in the columns confined with CFRP was minor compared to that of the specimens without CFRP confinement; additionally, the CFRP wraps delayed core failure in the column. Fig. 6 also shows that major damage in the specimens occurred in the upper part of them, which was also observed in the ...
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... a thin layer of concrete adhered to the CFRP fabric was observed, implying adequate bonding between concrete and the CFRP sheet. Fig. 6 shows that spalling of the concrete cover in the columns confined with CFRP was minor compared to that of the specimens without CFRP confinement; additionally, the CFRP wraps delayed core failure in the column. Fig. 6 also shows that major damage in the specimens occurred in the upper part of them, which was also observed in the specimens studied by Turgay et al. [16]. These authors argued that damage is mainly concentrated over a specific branch of the column under concentric loading, due to the heterogeneous nature of the concrete. Fig. 6b shows ...
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... in the column. Fig. 6 also shows that major damage in the specimens occurred in the upper part of them, which was also observed in the specimens studied by Turgay et al. [16]. These authors argued that damage is mainly concentrated over a specific branch of the column under concentric loading, due to the heterogeneous nature of the concrete. Fig. 6b shows the confining effect of CFRP sheets on failure modes of concrete columns with longitudinal reinforcement only. The specimen with longitudinal reinforcement only (CL) exhibited cover spalling so the bars buckled and the column lost axial load carrying capacity. In the specimens with both longitudinal reinforcement and CFRP ...
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... modes of concrete columns with longitudinal reinforcement only. The specimen with longitudinal reinforcement only (CL) exhibited cover spalling so the bars buckled and the column lost axial load carrying capacity. In the specimens with both longitudinal reinforcement and CFRP confinement (CW1L and CW2L), the longitudinal bars did not buckle (see Fig. 6b) and, therefore, they continued to contribute to the axial strength of the column; in fact, f' cc for the specimens CW1L and CW2L was 27% and 54% greater than the corresponding strength of the specimen CL, respectively. The testing machine reached its maximum loading capacity (about 2000 kN) during testing of the specimens CW2LV1R2, ...
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... of the specimen CL, respectively. The testing machine reached its maximum loading capacity (about 2000 kN) during testing of the specimens CW2LV1R2, CW2LV2R1 and CW2LV2R2 and, therefore, these specimens did not reach their compression capacity. However, the CFRP fabric of the specimens exhibited some degree of horizontal tearing, as shown in Fig. 6d, 6e and ...
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Citations
... Three specimens were tested to measure the mechanical properties of each material. In case of CFRP, the measured properties were those reported by Carrillo et al. [13] in a companion study. ...
Carbon Fiber Reinforced Polymers (CFRP) can be an alternative material to retrofit thin and low-rise concrete walls. The literature review reports no predictive backbone models that include the deformation associated with the main limit states of concrete panels retrofitted with CFRP fabrics. This paper aims to describe a backbone model to predict the shear strength and strains associated with the peak shear strength (max) and the loss of lateral resistance (llr) limit states of thin concrete panels retrofitted with CFRP strips. A model to correlate the shear strength associated with the max and llr limit states between panels and walls was developed to extrapolate the response from panels to walls. The experimental program includes cyclic diagonal compression tests of 15 panels. The results obtained allowed analyzing the hysteresis curves, the shear strengths and strains, and the energy dissipation associated with the max and llr limit states in the panels. The response of specimens retrofitted with CFRP were compared with those retrofitted with conventional methods, and with specimens that comply the minimum web shear steel ratio. The response measured in the panels showed that the dissipated energy associated with the limit states depends on the volumetric ratio, the inclination, and the number of CFRP strips. Results also demonstrate that performance of panels retrofitted with CFRP strips outperforms that of panels with the minimum web shear steel ratio.
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The axial compression strength of concrete columns has been proved to be significantly enhanced by external confinement. In this perspective, the use of Fiber-Reinforced Polymers (FRPs) has been extensively studied. In practical applications, the FRP-confinement is installed on loaded columns, which can already be significantly deformed, while theoretical models neglect this aspect. This paper concerns a new experimental investigation on the possibility that a pre-existing axial load affects the FRP-confinement of concrete. The research program also aimed at the development of a new analysis-oriented-model for the prediction of the compressive strength of FRP-jacketed concrete columns, depending on the level of the axial load, acting before the confinement. For this purpose, series of small-scale concrete cylinders were first loaded, then confined with Carbon FRP, and finally subjected to destructive pure axial compression tests. Four different levels of pre-existing loads were simulated, including the un-loaded condition.
In this study, lack of strength, stiffness, energy dissipation and ductility characteristics of the improperly repaired RC square columns were examined and the recoverability of seismic performance with the external Carbon Fiber Reinforced Polymer (CFRP) confinement was investigated. A total of six RC columns were tested for three times with different test stages; as-built, improperly repaired with Normal Strength Concrete (NSC) and retrofitted with CFRP confinement. In the first tests, relatively high axial load (0.40Acfc) and cyclic lateral load up to 15% lateral strength loss were applied to expose heavy damage on test columns. After that, the damaged columns repaired by using NSC and retested under the same loading conditions. In the first two test stages, the drift ratio at the end of tests was approximately 5%. The lateral strength, stiffness, ductility and energy dissipation characteristics of the improperly repaired columns dramatically decreased. At the last stage tests, the stiffness of strengthened columns was considerably reduced due to the damage that occurred in the concrete core after the two pre-damage phases. The lateral strengths of the CFRP retrofitted columns did not change much compared to the as-built columns because of the quality of the repairing concrete (26 MPa and 54 MPa) and the strain hardening behavior of steel reinforcement. Compared to the as-built columns, the cumulative energy dissipation capacities of columns were significantly increased, however, ductility increase was not achieved for all specimens because of the dramatic loss of stiffness.
