Seismic Retrofitting of Corroded Reinforced Concrete Columns Using Carbon Composites

ACI Structural Journal, May/Jun 2007 by Aquino, Wilkins, Hawkins, Neil M

Column 1, retrofitted with a continuous jacket, failed at a load and displacement significantly lower than those of the control column. Pinching, as in other cases, was associated with bond-slip failure at the dowel reinforcement. The lack of rigid body motions shown by this column reaffirms the bond-failure hypothesis. In contrast with the behavior shown by Columns 2 and 3, pinching in Column 1 occurred before yielding of the reinforcement, as confirmed from strain measurements during the test.

To investigate the behavior observed for Column 1, crosssectional cuts were made after cyclic testing was completed. As was the case for Column 2, it was again observed that the consolidation of the repair concrete around the column and dowel bars in Column 1 was poor compared with that for the same concrete in Column 3. It was also evident that the compaction in Column 1 was by far the worst of three columns, explaining the observed bond slip failure. Therefore, the cause of premature failure of Column 1 can be attributed to poor consolidation of the repair material.

Although Column 5 could not be tested to failure, it was determined that the retrofitting of this column was satisfactory at least with respect to its load capacity. The maximum load measured during the test was 152 kN (34 kip), 8% higher than the yield load recorded for the control column and almost the same level as the yield loads recorded for Columns 2 and 3. Furthermore, the strain gauges installed in the composite bands registered low levels of deformations in the CFRP, indicating that only limited damage occurred in the concrete. Furthermore, the tests performed on Columns 1, 2, and 3 showed that loss of load and displacement capacity was associated with circumferential strains above 0.1%. The maximum circumferential strain recorded in Column 5 was below 0.025%, indicating little damage accumulation in the concrete.

With the retrofitting techniques used in this investigation, the structural capacities of corrosion-damaged bridge piers can be restored and possible seismic deficiencies corrected. It is imperative that non-destructive testing techniques be used to assess the internal condition of the concrete after the retrofitting is performed as evidenced by the inadequate load-deformation behavior of Columns 1 and 2 due to poor consolidation of the repair concrete.

CONCLUSIONS

This investigation showed that: 1) advanced composite materials (ACMs) are a viable alternative for the repair and seismic upgrading of corroded columns. Columns retrofitted properly with carbon composite (CFRP) wraps had load and ductility capacities matching or exceeding those expected for an undamaged seismically designed column. Load and ductility capacities exceeded those of an undamaged control specimen with an inadequate length lap splice at the column to foundation beam connection; and 2) the use of external currents is feasible for inducing corrosion in large-scale laboratory tests.

ACKNOWLEDGMENTS

The authors wish to thank the Illinois Department of Transportation and the Federal Highway Administration for its support on this project and Masters Builders, Inc., for supplying the carbon composite system used in this research.