SEISMIC RETROFITTING OF EXISTING REINFORCED CONCRETE BUILDINGS

Abstract

Recent earthquakes in many parts of the globe have revealed the issues regarding the vulnerability of existing buildings. The existing buildings, which were designed and constructed according to earlier codal provisions, may not satisfy the requirements of current ,seismic code and design practices. Many reinforced concrete buildings lying in active seismic zones, may suffer moderate to severe damages during future ground .motions. Therefore it is essential to prevent unacceptable hazards to property and life of occupants, posed during future probable earthquakes. Building which were damaged in the past earthquake or the existing building which are deficient to resist seismic demands for deisgn basis earthquake need seismic retrofitting for better performance in future earthquake motion. The seismic rehabilitation of such buildings by retrofitting is a challenging task that structural Engineers face today. The success of mitigating disaster in an earthquake lies in the implementation of a comprehensive earthquake preparedness program. Preparedness and awareness are the keywords for earthquake protection of structures and prevention of loss of life is possible by retrofitting of existing seismically deficient structures. The present dissertation work deals with the seismic retrofitting of a 14 storied existing reinforced concrete building located in zone IV. The study comprises of seismic evaluation and retrofitting of R. C. building by addition of shear walls at strategic location. iii First seismic evaluation is carried out on the basis of 3D elastic, linear dynamic analysis. In the evaluation process capacity of the members are computed according to Indian design aids (IS: 456-2000 & SP-16) using developed software and earthquake demands of the members for revised draft code spectra for rock site with 5% damping are calculated using STAAD-1[1 (1997) software. The analysis shows that the building designed as per provisions of IS: 456-1978 using limit state of method of design, and seismic code IS: 1893-1984, is inadequate for provisions of revised draft code. After retrofitting of the building by addition of shear walls analysis results shows that addition of shear walls is just enough to achieve good performance in future earthquake. A parametric study is also carried out to study the effectiveness of the location of shear walls. The study concluded that providing shear walls in the external frames are more effective to increase the stiffness of the building than providing shear walls in the internal frames. But providing shear walls in the internal frames is more effective way of reducing base shear for high rise ., buildings. iv