Seismic Durability of Retrofitted Reinforced-Concrete Columns

The seismic performance 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 \If\N’\I\dcA\dg\N 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.