Plastic analysis and twist capacity of high-strength concrete hollow beams under pure torsion

In this article, a study on the plastic behavior and twist capacity of High-Strength Concrete (HSC) hollow beams under pure torsion is presented. The results of 16 tested beams are used to perform the plastic analysis. The plastic twist capacity of the beams was studied by using a Plastic Trend Parameter (PTP). This parameter was defined from the plastic local twist “versus” total twist curves of the test beams. It was shown that PTP is a good parameter to reflect the degree of the experimental twist capacity of the tested beams. The analysis with PTP shows that some plastic behavior of HSC hollow beams under torsion exists but is very narrow. Two study variables were also considered: the concrete compressive strength and the torsional reinforcement ratio. It is shown that PTP seems to decrease slightly as concrete strength increases. It is also shown that a high reduction of PTP exists with the increase of torsional reinforcement ratio and that the top limit to ensure some plastic twist capacity is approximately 1.30%. Some important codes (American, Canadian and European) are analyzed in the light of the plastic twist capacity observed for the tested beams. It is shown that the actual American code is the most appropriate by imposing a maximum and minimum value for the reinforcement ratio.