RESERVE STRENGTH INDEX IN SEISMIC EVALUATION

The structure's ability to survive an earthquake can be adjudged in terms of the expected damage of the structure after the earthquake. Damage is a qualitative term and lots of subjectivity is thus involved in the quantification of damage to a structure. Damage can be quantified using a damage index. Several damage indices have been defined and established through series of correlation and evaluation works by many researchers. Damage indices are defined as functions, which are finally related to a particular structural damage. A number of response based damage indices are available to be used for seismic vulnerability assessment for given structural system. Damage indices best suited for the nonlinear structural analysis are the right candidate for the seismic vulnerability assessment of existing building because such building which are supposedly deficient or at least doubtful for its seismic capabilities are expected to cross elastic limit and will make excursions in inelastic range. The empirical damage indices are mainly based on observed seismic damages to similar type of construction during past earthquakes. These indices as based on damage surveys may be subjective and individual bias, but they provide enough and useful information on the overall seismic performance of structural systems. However, empirical evaluations do not lead to rationally predict the reserve strength and response characteristics of the structure with a specified degree of damage. The idea of describing the expected degree of damage to existing building under anticipated future earthquake by a number on a predefined damage scale in the form of damage index related to structural response calculated on a rational and simple base is attractive for such studies. Adaptive Static Pushover analyses and Reserve Strength Index (RSI) have been used to study seismic vulnerability of building cases representing symmetric as well as asymmetric structures considering 6-and 12 storey RCMRF buildings.