Concrete Columns with Lateral Prestressing

Short concrete columns (height/width $\mathrm{ratio}=3$) were prestressed laterally using evenly spaced layers of orthogonally placed high‐yield steel (HYS) bolts in preformed ducts. No vertical (axial) reinforcement was used. After prestressing, the bolts (some of which were strain‐gaged) were grouted into their ducts. When the columns were loaded axially, the bolts acted in direct tension, in reaction to the lateral expansion of the concrete and offered a confining force to the concrete. In spite of the force being nonuniform, the bolt‐reinforced columns exhibited substantial strength and ductility gains over companion columns made of plain concrete. This paper reported tests in which both concrete strength and the magnitude of prestress were varied. The relationship between confinement and the experimental factors, and how they affect column strength and behavior, was described in detail. Some differences between steel‐confined and hydraulically confined concrete were identified. Reloading tests showed that bolt‐reinforced columns severely damaged by overloading retained most of their axial strength, but with reduced stiffness.