Development of hybrid ECC columns subjected to concentric and eccentric loading

In recent years, significant attention has been given in previous studies to improve the performance of structural members. It would be useful to further improve in this approach. This study was undertaken in order to investigate the structural behaviour of newly developed Engineering Cementitious Composites (ECC) columns subjected to concentric and eccentric loading. These columns were experimentally formulated using a hybridization of steel and polypropylene fibers. Two ratios were adopted for the steel fibres 0.5% and 1%, whilst the polypropylene fibre was kept constant at a ratio of 0.5% for all of the ECC columns. The eccentric loads were applied at two eccentricities: small (h/6) and large (5 h/12). The effect of slenderness ratio was taken into consideration at two values; 6 and 8. A comparison was also made with the behaviour of self-compacted concrete and traditional ECC columns containing either steel or polypropylene fibres. The vertical and lateral deformations as well as the maximum load at failure were noted. Amendments were performed on some of the related formulas suggested by the code of practice. The results obtained showed that the hybrid ECC columns exhibited higher load carrying capacities when compared with those of both self-compacted concrete and traditional ECC columns. The percentage increase reached 30%. The hybrid ECC column samples containing 1% steel fibre did not show a signification difference in the load-deformation behaviour when it compared with that containing 0.5% steel fibre. The values of eccentricity and slenderness ratio governed the global behaviour of the tested columns. The predicted load carrying capacities of the ECC columns using the existing code formulas need a magnification factor in case of concentric test, and to take into account the fibres ratio when calculating the area of steel reinforcement for eccentric loading.