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This paper shows a theoretical model for reinforced concrete beams subjected to torsion and strengthened with composite of carbon fibers (CFRP). It is based on researches of Michael Collins and collaborators and approaches the theory of diagonal compressive field. This model was inserted in a mathematic software, due to the need of interactions to obtain the torsion and torsion angles. The validation of theoretical values was realized through the results of tests obtained from the literature and it was understood that the model is valid and conservative for the ultimate torsion in most of the studies carried out. However, the beams that had the geometric ratios width and height b/h < 0.5 and the ratio between the cover and the smaller dimension of the d/cob element ≤6 had not so accurate results.

Two sets of reliability analyses for two beam series strengthened with carbon fibre composites (CFC) in different ways and subjected to torsional moments are described in this paper. The analyses consider three failure functions and the system is regarded as a series system formed by these three limit state modes. Five random variables are taken into account in the first set of analyses. The analyses are performed for different torsional moment ratios, defined as the ratio of the torsional moment due to live loads to the total torsional moment. The system reliability indexes and the factors of importance associated with each random variable are obtained. In the second set of reliability analyses, only the two most relevant random variables selected in the first set of analyses according to the values of their factors of importance are considered, and new reliability indexes are determined. The examples show that despite the constant value of the total torsional moment, the increase in the torsional moment ratio leads to a decrease in the system reliability levels. The fact that the values of the reliability indexes obtained in both sets of reliability analyses are very similar validates the efficiency of the sensitivity analyses.

This paper describes an analytical study about the bond between concrete and glued carbon fiber composites (CFCs) using data of 2 experimental researches. A total of 27 double compression-tension tests were carried out on specimens with 2 concrete cubes (fixed and movable) connected by carbon fiber strips on opposite sides. The variables were concrete strength, with the evaluation of 9 specimens with strength of 20.5 to 38.1 MPa, with monotonic loading and smooth surface for all specimens, and 18 specimens with strength of 23.2 to 40.8 MPa, with monotonic loading and loading/unloading cycles and different concrete surfaces (smooth face and rough face). The test results showed that the ultimate bond stress slightly varies according to concrete strength in the analyzed zone. The strains of CFCs and concrete were measured, allowing the calculation of bond stress and the corresponding mean strain, which were compared with the values obtained by the expression given in the international codes. The prediction of the old expression applies to steel plates strengthening method, and the results of a more recent expression of CFC glued to concrete given by fib Bulletins and Model Code 2010 are compared with test results. The experimental results provided graphs and correlation curves for bond stress vs maximum strain, energy of fracture vs bond stress and a relationship between the mean shear strain and concrete strength. The expression for fracture energy given by fib Bulletins and Model Code 2010 varies with concrete strength f c and a reasonable agreement with test data was achieved. K E Y W O R D S bond, bond by tension-compression test, carbon fiber composites

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It is known that design deficiencies in shear design are more dangerous than bending, as shear failures can occur in a fragile way and without possibility of redistributing internal forces. Unlike bending design, designing for shear loads by different standards can generate significantly different results for the same element, as long as design models have been under discussion for many years. This paper analyses the evaluation of the behavior of the combined bending and shear loads in reinforced concrete beams for different pairs of these forces. For this purpose, the verification presented in ABNT NBR 6118 was used and compared to a more improved theory currently used, the Modified Compression Field Theory - MCFT. This theory is able to predict the relationships of specific loads and strains, as well as the shear strength of sections with great precision, being parameterized by several tested elements. As the use of this theory is not practical for manual calculations, the Response-2000 software, developed at the University of Toronto by Evan C. Bentz, was used. The program allows the analysis of beams and columns subject to moments, shear forces and axial loads, for any type of geometry, material properties and reinforcement arrangement, resulting in accurate responses of the behavior of the sections using MCFT as a basis.