RETROFITTING OF A RC FRAME BUILDING USING FRP WRAPPING

Abstract

Many RC buildings, in India, have been constructed without giving proper attention to earthquake forces. Especially buildings constructed in 1960's and before that have not been designed for earthquake forces. To ensure safety of such buildings against earthquake forces, they require retrofitting. There are different retrofitting methods used for different structures, depending on the particular conditions and performance levels desired. For existing building it is very difficult to execute a retrofit scheme, as such buildings are under operation. So we have to device such a retrofitting method, which is fast in construction and easy in application. FRP wrapping is a very promising technique from this point of view. In this method individual component of building is retrofitted as per requirement to improve the overall performance of the building. In this study an existing hospital . building has been considered. This building was constructed in 1963 and was not designed for seismic forces. This building has shear walls in transverse direction and frames in longitudinal directions. The enhancement in the performance of the building against seismic forces has been evaluated, using retrofitting with FRP wrapping. To improve the performance of a building during earthquake, it is essential to improve the performance of its components. Existing building component behavior has been studied by moment curvature and axial force moment interaction analysis. From this analysis strength and ductility of existing and retrofitted sections have been evaluated. The steel stirrups confined concrete has been modeled as per Mander model and FRP confined concrete has been modeled as per Lam and Teng model, while reinforcing steel has been modeled with IS 456:2000 model. The usable strain limits has been considered as per FEMA 356 and ATC 40 guidelines. Existing building has been modeled in SAP 2000 V 10.0.5 and analyzed for gravity & seismic forces. It has been found that structure is not safe against gravity loads as per current code of practice. Pushover analysis has been carried out to study the performance of the building as per FEMA 356 and it is observed that building is not safe against the design seismic forces. iii The existing building structure has been retrofitted with GFRP wrapping. The yielding beams and columns have been wrapped with different number of GFRP layers. It has been observed that the building can achieve the required performance level in longitudinal direction with three layers of GFRP wraps. But the desired performance level could not be achieved in the transverse direction. iv