A model for predicting the displacement ductility index of HSC beams
It has been proven that helices confinement provided in the compression zone of over-reinforced HSC beams improves the ductility. According to the codes of practice, there is a limit to the ratio of longitudinal reinforcement for a particular cross section. However more longitudinal reinforcement can be installed if the flexural strength required is more than the capacity of a particular cross section, where such a section becomes under-reinforced rather than over-reinforced section. It is basic knowledge that over-reinforced sections fail in a brittle mode but installing helical reinforcement with a suitable pitch in the compression zone will reduce this unwanted effect. Formulating the displacement ductility index for an over-reinforced helically confined HSC beam is required to study and focus on non-dimensional factors. The relationship between displacement ductility index and non-dimensional factors involves a large number of variables, most of which are related to helical confinement. The behaviour of over-reinforced helically confined HSC beams is complex and therefore several variables must be investigated to develop an empirical formula. The development of a model to predict displacement ductility index of over-reinforced helically confined HSC beams is presented in this paper. The displacement ductility index is affected by variables such as the volumetric ratio of helical reinforcement, helical pitch and helical yield strength. The results obtained from this model are compared with the experimental results.
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