HAZARD MITIGATION AND EXTERNALLY FRP RETROFITTING OF RC BUILDINGS SUBJECTED TO NEAR-FAULT GROUND MOTIONS HAVING FORWARD DIRECTIVITY

Ground motions in the near field of a rupturing fault differ from ordinary ground motions, as they contain a large energy, or “directivity” pulse. This pulse can cause considerable damage during an earthquake. Failures of modern engineered structures observed within the nearfault region in the recent earthquakes have revealed the vulnerability of existing RC buildings against pulse-type ground motions. This may be due to the fact that these modern structures had been designed primarily using the design spectra of available standards which was developed using stochastic processes with relatively long duration that characterizes more distant ground motions. Many recently designed and constructed buildings may therefore require strengthening in order to perform well when subjected to near-fault ground motions. This paper presents the results of a study of the response of typical existing RC buildings to near-fault ground motions and the potential improvements achievable after FRP retrofitting of the buildings. Results show that in case of near-fault records, they impose higher demands in comparison to far-fault records, though the maximum drift is generally concentrated at the middle story levels. It is demonstrated that strengthening with FRP is very effective in reducing drift demands for structures for a wide range of natural periods. The rehabilitated buildings possess an elastic stiffness 1.4 times that of the original buildings and have a total shear force capacity, 1.5 times that of the original buildings. The cumulative energy dissipation for rehabilitated specimens is 2.3 times that of the original building, on average.