A Systematic Methodology for Structural Assessment and Vulnerability Estimation of Structural Members of Existing Reinforced Concrete Buildings

Existing reinforced concrete buildings generally exhibit limited resistance in the failure limit state, primarily due to inadequate reinforcement detailing that does not satisfy modern seismic design requirements, whereas they show adequate resistance in the yielding limit state, where concrete cracking is mainly due to bending. This yield-governed behavior also characterizes modern earthquake-resistant structures, which can tolerate localized failure at beam and column ends while maintaining overall integrity. These critical regions, precisely defined in this work, are short relative to the member length, allowing the remaining elastic yield length to contribute to global resistance. Even under strong earthquakes, most columns and beams remain in the yielding range. Beyond assessing the capacity of existing buildings, it is therefore important to identify vulnerable members likely to require strengthening. Given the limited literature on designing in the yielding limit state, the authors recently focused their research on this specific topic and developed unified design software, applicable to different materials and both yielding and failure limit states. Building on that framework, this study outlines the key orders of magnitude needed for strength assessment and for effective retrofitting strategies.