Seismic Retrofitting Strategies For R C Structures

Abstract

Analysis and design of new Reinforced Concrete(RC) buildings are straight forward since since they comply the standards for the construction and practice. On the other hand analysis of existing RC building offers lots of complexity due to numbers of parameters like non-compliance with recent criteria of standards, reduction in strength of materials due to age and sustained loading, change in properties due to physical and chemical attacks etc. Hence strength evaluation of existing structures becomes challenging and requires well formulated methodology that accounts for all the parameters. Nowadays, seismic evaluation of existing RC Buildings becomes important since most of them found to be seismically deficient against recent criteria of seismic code. Deficiencies in RC building may be at member level (local) and/or structures level (Global), therefore it is important to identify seismic deficiencies for RC building properly to evaluate its strength and undertake either Restrengthening or Retrofitting of RC building if found deficient. The present work aims to compare seismic retrofit design carried out using Force Based Design(FBD) and Displacement Based Design(DBD), while FBD considers force as basic parameter, DBD lays importance on inelastic displacement of the structure and hence is more realistic. A G+2 Storey existing RC school building is considered which is about 23 years old. The school building is designed as per prevailing seismic code and seismic deficiencies are derived. The school building is also designed using DBD and corresponding seismic demand for the building is calculated. Comparison among FBD & DBD are carried out in terms of Base shear, Storey displacement, Storey force and Storey shear. The comparison of deficiencies is made in terms of Demand-Capacity ratio (DCR) of deficient members and suitable retrofitting strategies like jacketing and FRP wrapping are also suggested. It has been found that seismic demand vary significantly for FBD and DBD with DBD reduces as compared to FBD. Thus, retrofitting measures reduces significantly if DBD methodology is adopted as compared to FBD methodology.