Unbonded Prestressed Columns for Earthquake Resistance

Modern structures are able to survive significant shaking caused by earthquakes. By implementing unbonded post-tensioned tendons in bridge columns, the damage caused by an earthquake can be significantly lower than that of a standard reinforced concrete bridge column by reducing the amount of residual displacement. Reducing the amount of damage will allow for speedy repairs on the bridge and minimal closure time. The objective of this research was to investigate new construction methods for unbonded post-tensioned bridge columns that will reduce the amount of damage caused by an earthquake. Two 0.4-scale columns containing unbonded tendons were selected for testing. The two columns are identical except for the amount of longitudinal reinforcement crossing the joint between the column base and footing. For the specimens to be true scale models, the amount of post-tensioning required in a full scale column was taken into consideration. The large amount of prestress needed in a full-scale column requires separate tendons being spread out around the center of the column cross section. Following an earthquake, the tendons may need to be inspected or replaced. Anchoring the tendons to the side of the footing as opposed to the base of the footing was introduced for ease of replacement. The introduction of the unbonded tendons showed a significant reduction in residual displacements.