Rapid Seismic Repair of Shear Damaged Concrete Bridge Columns by Transverse Prestressing

Abstract eng:
Reinforced concrete bridge columns subjected to strong earthquakes indicate that they may suffer from various types and levels of damage. One of the most common causes of seismic damage in shear-dominant columns is diagonal tension cracking, which may or may not result in irreparable damage. A rapid seismic repair technique was developed through experimental research, involving external post-tensioning damaged columns in the transverse direction. The technique was developed as an extension of a similar technique that had been developed for column retrofitting, known as the “RetroBelt” technology. The repair method involves the placement of seven-wire strands around circular, square or rectangular columns and applying prestressing by means of a hand held hydraulic jack and specially developed anchors. The prestressing tends to close shear-induced diagonal cracks, improving aggregate interlock mechanism, while also providing additional shear reinforcement. The technique was verified by testing large-scale columns under simulated seismic loading. The specimens were designed to reflect seismically deficient columns with widely spaced ties. They were subjected to constant axial compression and incrementally increasing lateral deformation reversals. The columns were initially damaged by lateral deformation cycles reaching up to approximately 1% lateral drift. Relatively wide diagonal cracks were observed, signifying the yielding of tie steel. The loading was then stopped and the columns were repaired by transverse prestressing. The repaired columns were then subjected to similar loading, with increasing levels of deformation. The results indicated that the shear failure was suppressed and the mode of behaviour was changed from shear to flexure. External prestressing also improved concrete confinement and resulted in 4% and higher lateral drift capacities. The paper presents the results of the experimental investigation and the repair design methodology developed.

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