The good performance of reinforced concrete structures is ensured by the transfer of stress linking a reinforcing bar and the surrounding concrete. The bond steel-concrete is a very complex phenomenon. This paper presents the experimental results of a program with specimens used in the pull out test with concrete strength of 20, 40, 60, 80 and 100 MPa and four different steel diameters: 12.5, 16.0, 20.0 and 25.0 mm. The test results indicated that the bond stress varied with the bars rib face angle, rib spacing, and rib height. The trends of the results were independent of the concrete strength with the test results, and design recommendations made as regards optimum rib geometries of deformed bars with high bond-slip characteristics.
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.
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