A PERFORMANCE-BASED APPROACH FOR THE DESIGN OF CONFINING STEEL IN TIED COLUMNS

A review of the development over the years of the ACI Code provisions for confinement is presented. Based on the available experimental evid ence, the current Code requirements for the amount of confinement stee l in tied columns are critically evaluated. It was concluded that the behavior of columns designed according to the ACI Code may vary from u nacceptably brittle to very ductile. While the amount of Code-required steel can be reduced in many cases, much larger amounts of lateral st eel are needed in other cases. A new design procedure is proposed in w hich the amount of lateral steel required is a function of the column ductility performance. The lateral steel content increases with an inc rease in the level of axial load, and depends on steel distribution an d the extent of lateral restraint provided to the longitudinal bars. F or any specific steel configuration, the procedure lends itself to a s imple design charr. The proposed method when applied to realistically- sized specimens rested by different investigators yielded excellent ag reement with the experimental results.