Behavior of Laterally Confined High‐Strength Concrete under Axial Loads

The empirical results of a test program studying the effects of rectilinear confinement in high‐strength concrete subjected to a monotonically increasing compressive axial load was reported. Twentyfour columns made of high‐strength concrete with compressive strength $f_c^{\prime }$ ranging from 12,130–13,560 psi (83.6–93.5 MPa) and rectilinearly confined with lateral ties and longitudinal rebars were tested. The stress‐strain behavior was studied with respect to the effects of the volumetric ratio of lateral ties, the concrete cover, and the distribution of the longitudinal steel around the core perimeter. Expected general improvements in the strength and ductility of the high‐strength concrete with rectilinear confinement was observed. The lateral steel confinement was not as effective as in low and normal‐strength concrete. Columns with four longitudinal rebars exhibited much less ductility than columns with eight longitudinal bars. All the specimens failed with a single shear failure plane. An empirical model for the stress‐strain curve of rectilinearly confined high strength concrete using three parameters: ($f_0\text{,}$ ${\epsilon }_0$), ($f_i\text{,}$ ${\epsilon }_i$), and ($f_{\mathrm{2i}}\text{,}$ ${\epsilon }_{\mathrm{2i}}$) was proposed. Equations for the parameters were developed.