مهدی نعمت زاده افروزی

Steel-reinforced concrete (SRC) columns, which are classified as composite columns, became the most widely used in recent years; because of their extensive advantages over the reinforced concrete and the steel columns. In this paper, the ductility index and its influential factors were explored to investigate the behavior of SRC columns. A straightforward approach was then proposed by establishing the necessary equations based on the plastic stress distribution method. Accordingly, an experimental program was performed on six SRC column specimens with two H- and cross-shaped steel sections and three eccentricity ratios of 0.4, 0.55, and 0.7. In addition, a finite element model was developed for numerical analysis using Abaqus software, which was verified by the experimental results. A total of 30 columns were thus analyzed for the parametric study where the effects of geometric and material variables, including steel percentage, concrete compressive strength, lateral tie spacing, and geometrical shape of the steel core on the ductility index of these columns were assessed. The results confirm that for the H-shaped column, reducing the lateral tie spacing ratio from 0.6 to 0.2 not only increases the ductility index to as much as 72%, it also induces a post-yield hardening in the load displacement curve and increases the bearing capacity by 20%. Subsequently, load-bending moment interaction curves were developed according to plastic stress distribution method cited in EC4 Code and then compared with those obtained through the software. Thus, normalized curves were presented as a means to design these columns.