This guideline provides a framework for the seismic evaluation of existing reinforced concrete buildings to assess their expected performance in future earthquakes. It outlines procedures for analysis, from simple linear methods to advanced non-linear pushover analysis, and provides conceptual strategies for seismic strengthening or retrofitting to achieve desired performance objectives like Life Safety.
Provides guidelines for the seismic evaluation and strengthening of existing reinforced concrete buildings.
Quick Reference Values
Typical performance objectiveLife Safety (LS) under Design Basis Earthquake (DBE)
Lower-bound strength of in-situ concrete0.67 times the characteristic cube strength
Rotation limit for primary beams at Life Safety0.02 radians
Rotation limit for primary columns at Life Safety0.015 radians
Minimum grade of new concrete for jacketingM25
Key Formulas
Demand Capacity Ratio (DCR) = Acting Force (Demand) / Member Capacity
Pushover Analysis: A non-linear static analysis where a structure is subjected to a gradually increasing lateral load pattern to determine its force-deformation curve.
Practical Notes
The first and most critical step is collecting accurate 'as-built' data, including structural drawings and material properties (through NDT and core tests). Inaccuracies here will render the entire analysis unreliable.
This code introduces performance-based design concepts (e.g., Life Safety, Immediate Occupancy) which are different from the force-based design of new buildings in IS 1893.
Non-linear static (Pushover) analysis is the recommended method for most important buildings as it provides a better understanding of failure mechanisms, ductility, and post-yield behavior.