Strength of Tied High-Strength Concrete Columns Loaded in Concentric Compression

The research described in this paper deals with the strength of reinforced concrete columns loaded in concentric compression, with particular emphasis on the issue of early spalling of the concrete cover. To investigate the behavior of tied reinforced concrete columns, a test program was established. Twelve columns were tested in three series under axial compression. The study shows that the longitudinal reinforcement is at yield at the spalling load, while the tie steel is not at yield at the point of cover spalling. After cover spalling, microcracking of the core leads to expansion of the core and activation of the confinement provided by the ties. The ultimate capacity of a concentrically loaded high-strength concrete (HSC) column is the maximum of the spalling load and the capacity of the confined core. Design recommendations are given.