SEISMIC RETROFITTING OF EXISTING REINFORCED CONCRETE STRUCTURES

Abstract

For a long time, structural deficiency has been one of the major issues in the construction areas. Even the newly built structures show seismic deficiency due to negligence of various factors and guidelines laid down by the Governing bodies. The structures already built might have become deficient according to the latest versions of the codes or the codes and detailing might not have been considered from seismic point of view. According to a census conducted by NDMA, 65-70 percent of the structures in India were either constructed before the latest versions of the code or have not been built earthquake resistant. A complete demolition and reconstruction of those structures is very uneconomical and thus the need of retrofitting arises. The structures may have become vulnerable due to many reasons which need to be overcome by several techniques. In our particular case, the building considered is the newly constructed building located in city and built by masons using the old thumb rules. The building can withstand gravity loads but is seismically deficient. The retrofitting techniques include the use of infill panels, shear walls, steel bracings, concrete and steel jacketing and energy dissipation methods. The comparison of the seismic demand according to the various editions of IS 1893:part 1 shows the increase in the demand along with the upgradation of the codes. Various seismic retrofitting techniques have different efficiencies based on the soil type and the height of the building. Higher buildings respond well to the tubular tension ties than the X-Bracings, soil type being the same. The efficiency of a particular retrofitting scheme, for instance, the use of steel bracings at a beam-column joint also depends on the type or model of the joint. Connections of the retrofitting scheme to the element being retrofitted are of utmost importance. The anchor bolts, for instance, show less strength if a higher tensile force is in play. This report is focused on the connections between steel and concrete using the anchor bolts. The types of anchor bolts also play a significant role in the performance under cyclic loading, on the basis of failure during high cycle fatigue or low cycle fatigue. Till date, we experience that the buildings frames retrofitted with shear walls show better performance than the buildings frames ii retrofitted with the bracings. For columns, reinforced concrete jacketing shows good results. A detailed study and review of the various retrofitting schemes for Reinforced concrete structures are present in the report. A detailed analysis of behaviour of steel X-Bracings in Open Ground Storey buildings is included in this report. Various retrofitting schemes which are essential for sustaining the older, vulnerable reinforced concrete structures are also considered. The report includes application of Shear walls and inverted-V bracings.