Comparative Study of Models on Confinement of Concrete Cylinders with Fiber-Reinforced Polymer Composites

The use of fiber-reinforced polymer (FRP) composites for strengthening and/or rehabilitation of concrete structures is gaining increasing popularity in the civil engineering community. One of the most attractive applications of FRP materials is their use as confining devices for concrete columns, which may result in remarkable increases of strength and ductility as indicated by numerous published experimental results. Despite a large research effort, a proper analytical tool to predict the behavior of FRP-confined concrete has not yet been established. Most of the available models are empirical in nature and have been calibrated against their own sets of experimental data. On the other hand, the experimental results available in the literature encompass a wide range of values of the significant variables. The objective of this work is a systematic assessment of the performance of the existing models on confinement of concrete columns with FRP materials. The study is conducted in the following steps: the experimental data on confinement of concrete cylinders with FRP available in the technical literature are classified according to the values of the significant variables; the existing empirical and analytical models are reviewed, pointing out their distinct features; the whole set of available experimental results is compared with the whole set of analytical models; and strengths and weaknesses of the various models are analyzed. Finally, a new equation is proposed to evaluate the axial strain at peak stress of FRP-confined concrete cylinders.     

Analytical modelling of plastic behaviour of uniformly FRP confined concrete members

A method is presented for the assessment and calibration of the elastoplastic behaviour of FRP confined concrete. The method is based on the evaluation of permanent deformations from observed experimental deformations and theoretical elastic response of confined concrete. The inelastic response of concrete and the parameters of its mathematical modelling are investigated. Closed form expressions are produced to relate the model parameters to the mechanical properties of the material. A strain-hardening Drucker–Prager model is developed which simulates both the hardening and softening material response with reasonable agreement to the experimental observations. The predictive ability of the model is verified through comparisons to numerous published experimental data and analytical models.     

Absorption of energy in fatigue loading of plain concrete

Existing partial damage hypothesis gives unsatisfactory results in estimating the fatigue of plain concrete. Volumetric, ultrasonic, and acoustic emission measurements have not been able to fully interpret the deterioration of concrete. Another parameter in this respect might be the absorbed energy by the loaded concrete. In this investigation a measuring system for registration of the absorbed energy is presented. The results achieved are affected by difficulties at the development of the measuring system. However, it seems as if the absorbed energy at failure of concrete was the same for static load and for fatigue load with different intensities.

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Résumé Les hypothèses de dommages partiels dont on dispose ne donnent pas de résultats satisfaisants pour estimer la fatigue du béton non armé. Les mesures volumétriques ultrasoniques et d'émission acoustique ne suffisent pas pour interpréter complètement la détérioration du béton. Un autre paramètre pourrait être ici l'énergie absorbée par le béton sous charge. Dans cette étude, on présente un système de mesure pour enregistrer l'énergie absorbée. Les résultats obtenus sont affectés par les différences de mise au point du système de mesure. Il semble cependant que l'énergie absorbée à la rupture du béton est la même sous charge statique et en fatigue avec des intensités différences.

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