Evaluation and comparison of capacity and rupture of elliptical columns, with and without casing, and application of single-layer and double-layer wrapping, under pure axial pressure

The effect of pure axial pressure on oval reinforced concrete columns made of normal (NC) and high-strength concretes (HSC) enclosed by a glass-fiber reinforced pipes (GRP) as well as a carbon -FRP was investigated. Behavior refers to the compressive capacity (CC) and ductility. The effect of concrete type, casing, wrapping and its layers were investigated. Totally 12 columns with 200*120 mm and 600 mm height were constructed; they were divided into 2 groups of NC and HSC; each group was divided into two parts of 3. The first part had a casing and the second part did not. From each part, first column lacked a reinforcing layer, second with one layer and third with two twisted layers. The wrapping and casing improved the columns, behavior. Using one and two wrapping layers increased the CC by 19.7% and 28.7% on average in the first and 11.0% and 28.7% in the second groups, respectively; use of casing resulted in an average increase in the CC of the columns in the first group by 4.15 times and in the second group by 3.51 times. Although the wrapping and the casing both create confinement, the casing has a much greater effect on improving the columns behavior due to its greater confinement, and the effect of the confinement on the behavior of the first group is also greater. Comparing the effect of casing enclosure with wrapping showed that the casing is much more effective, and its effect is more on columns made of NC.