Compressive behaviour of ECC confined concrete partially encased steel composite columns using high strength steel

When using high strength materials in concrete partially encased steel (CES) composite columns, the major issues encountered are strain incompatibility of high strength steel and high strength concrete, premature concrete spalling and explosive brittle failure with poor ductility. In order to improve the compressive behaviour and ductility of CES columns, Engineered Cementitious Composites (ECC) encasement is proposed as a confinement and protection layer for concrete and steel, respectively. In order to evaluate the effectiveness of ECC cover on performance of CES columns, compressive behaviours of ECC-CES short columns were experimentally investigated to study the effects of material strengths, ECC encasement thickness, steel section shape and column's aspect ratio. Findings were discussed and reported in terms of failure behaviours, load-deformation responses, post-peak ductility and toughness. Test results suggested that while only an insignificant increase of axial compressive resistance was observed, ECC encasement improved failure behaviour of ECC-CES columns by effectively controlling brittleness and explosive spalling of high strength concrete. ECC-CES generally showed improved ductility and energy absorption capacity but the strength enhancements were minimal. Reliability of current design codes in predicting the column ultimate strength was investigated and a new approach based on effective stress method was proposed. Finally, a 3D non-linear numerical model was also developed to predict the compressive behaviours of the proposed form of columns and a small scale parametric study was conducted.