Performance of segmental self-centering rubberized concrete columns under different loading directions

Segmental self-centering columns are an advantageous construction choice in earthquake prone areas due to their minimal or even zero residual deformation and their low repair/downtime costs. This research investigated the behavior of segmental rectangular column members with a high cross-sectional length to width ratio under different loading directions, with the aim of potentially extending the concept of segmental self-centering columns to wall members, such as shear walls and retaining walls. The main parameters of this study were the direction of loading: in-plane (strong-axis bending) and out-of-plane (weak-axis bending), provision (or absence) of reinforcement, and the type of concrete material (conventional concrete or rubberized concrete). Eight concrete columns with a cross-sectional length to width ratio of 2.5 and consisting of three concrete segments with dry joints in between, were tested under reversed-cyclic lateral loading. A pre-stressing force of 100 kN, corresponding to a stress of 2.8 MPa on the column, was applied using unbonded post-tensioning (PT) bars. The results indicated that although in-plane loaded columns had a higher load capacity, they exhibited a less ductile response, higher level of damage and higher loss in the PT force, compared with the out-of-plane loaded columns. The total equivalent viscous damping and its variation was very small in all tested specimens, and it increased slightly as the drift ratio increased. Empirical equations were developed to express the damping as a function of drift ratio. It was also concluded that in the out-of-plane loaded specimens, the effect of reinforcement on the load-displacement response was insignificant. In rectangular columns with high length-to-width ratio, under out-of-plane loading, if a minimum level of axial pre-stressing is applied (to prevent shear or sliding failure), no structural reinforcement is required. In addition, the strength reduction due to using rubber in concrete at the structural level was much lower than that at the material level. The results of this study can potentially be applied to segmental concrete walls due to the high length-to-width ratios of the tested columns.