New
Seismic Retrofitting Technique
Experimental
research was conducted to develop a rational and economical retrofit
technique for concrete bridge columns. It involved testing seven
full-scale reinforced concrete bridge columns under simulated
seismic loading. The columns had either a circular or a square
cross-section and represented pre-1970's design practice. The
reinforcement arrangement consisted of 12 longitudinal bars with
ties placed at 300 mm spacing.
The
retrofitting scheme consists of transverse prestressing steel
to externally reinforce columns for shear, while also improving
concrete confinement. The effectiveness of these schemes were
determined experimentally in the laboratory.
Prestressing
wires were anchored using a newly developed twisted ring anchor.
In
order to enhance the confinement of a rectilinear column, the
externally applied pressure must have components perpendicular
to the column face, and be as uniform as possible for increased
effectiveness. Thus, a hollow structural section (HSS) was selected
as external hoops to uniformly distribute forces exerted by the
prestressing strands. The strand was placed directly on top of
an HSS section and raised in 3 locations along each column side
by means of half-disc shaped steel wire raisers to develop perpendicular
force components.
