RETROFITTING EXISTING CONCRETE COLUMNS BY EXTERNAL PRESTRESSING

摘要

A large number of existing reinforced concrete structures, suchas buildings and bridges, if subjected to abnormal loads, such asthose expected during earthquakes or bomb blast, may experiencesignificant inelasticity in their critical regions. It is economically notfeasible to replace the entire existing infrastructure with new andimproved structures; retrofitting provides the only solution to theproblem of seismically and otherwise structurally deficient existingstructures. A new retrofitting process has been developed to improvestrength and deformability of existing reinforced concrete columns(10). The process involves determining column (10) critical regions,identifying critical stresses that may lead to brittle shear and/orcompression failures, determining external prestressing to overcomesome of these stresses and to provide lateral confining pressure toimprove the ductility of compression concrete. External prestressingis provided by placing prestressing hoops (14) around the column (10)at predetermined locations. Each hoop (14) includes a strand (16)that encircles the column (10) with its ends fixed under tension to ananchor (1S). The invention is applicable to concrete columns (10) ofany geometric cross section. For circular columns prestressing may beapplied directly on the surface of the column (11) by the strands (16).For columns (10) with rectilinear geometry such as square, rectangularand other polygonal cross-sectional shapes, additional hardware (76,77, 85, 86) is necessary between the strand (16) and the flat surfaces(74) to distribute the prestressing force as evenly as possible on thesurfaces (74) of the column (10). External protection of hardwareagainst corrosion, fire and vandalism may be carried out by meansof fiber reinforced or plain concrete jackets, shotcreeting or similarsprayed applications of cement based materials (62), and differenttypes of paints.