Haunch retrofitting technique for seismic upgrading deficient RC frames

Haunch retrofitting technique has been employed, primarily to stiffen the beam-column connections that controls the hierarchy of strength within the beam-column members, and avoid joint shear hinging of RC frame structures, subjected to earthquake imposed lateral loads. Shake-table tests were performed on a total of nine (09) 1:3 reduced scale two-story RC frames, including five (05) as-built and four (04) haunch retrofitted models, to develop structures’ damage scale and obtain their seismic response parameters. A representative finite element based numerical model was prepared in SeismoStruct and validated against the experimental response. A suit of seven natural accelerograms were retrieved from the PEER NGA strong ground motions database and employed for incremental dynamic analysis of structural models, in order to derive seismic fragility functions for as-built and retrofitted structures. Vulnerability curves were derived for the structures, correlating the mean damage ratio with the seismic intensity. Uniform hazard curves, obtained for candidate cities in moderate and high hazard zones, were employed to derive the structures’ loss exceedance curves for calculating the expected average annual loss. The net present value of the annual avoided repair cost was quantified, and critically compared with the retrofitting cost, to evaluate the viability of haunch retrofitting technique for seismic upgradation of deficient RC frame structures for risk mitigation.