Seismic Durability of Retrofitted Reinforced‐Concrete Columns

The seismic performances of four (three retrofitted and one control) half‐scale, circular, reinforced‐concrete columns were studied. The columns were 10‐ft high, 18‐in. diameter cantilevers. The longitudinal flexural steel was spliced to the foundation dowels just above the fixed base. A concentric axial load of 0.20 $f{\prime }_c{A}_g$ was continually applied during testing. The free ends of the cantilevers were translated to produce a maximum displacement of four times that necessary to produce yield in the longitudinal reinforcing steel. This loading was repeated with both positive and negative displacements in a quasistatic manner until the lateral forces required to produce these displacements approached zero. The measure of seismic durability used was the number of such cycles that a column sustained before losing structural integrity. The laboratory arrangement was intended to model the arrangement of bridge columns constructed in the 1950 to mid‐1970 era. Three columns were retrofitted with prestressed, externally located circular hoops at intervals along the lower 4 ft. The spacing and size of these ties varied from column to column. The control column sustained less than two cycles before losing structural integrity; the retrofitted columns sustained a minimum of 12 cycles.