Evaluation Of Collapse Indicators For Seismically Vulnerable Reinforced Concrete Buildings

Older reinforced concrete buildings can be prone to column shear and compression failures during earthquakes because of inadequate transverse reinforcement. Cities in seismic areas still have large inventories of older and potentially deficient buildings. To analyze every building and estimate its vulnerability in detail is costly. A simple method to rank quickly older buildings according to their seismic vulnerability is needed to help engineers prioritize the use of resources for rehabilitating the most vulnerable buildings. Four indicators of building damage or collapse were evaluated using numerical analysis and prior data from building surveys: column index (Hassan & Sozen, 1997), R factor, ratio of column shear capacity to plastic shear demand, and ratio of column moment capacity to beam moment capacity. Idealized building frames were studied using nonlinear numerical analysis. Numerical models of these building frames with different spans, column sizes, numbers of floors, and transverse reinforcement ratios were analyzed with 44 ground motion records. Each numerical analysis used an algorithm to estimate whether a hypothetical building represented by a numerical model was likely to be severely damaged by strong ground motion. Among the four indicators studied, the column index was observed to be 1) the simplest and 2) the one with the best correlation with estimates of vulnerability to damage. Approximately 3/5 of the hypothetical building frames represented by numerical models with column indices not exceeding 0.2% were classified as buildings likely to be severely damaged by strong ground motion. Buildings with column indices not exceeding 0.2% were 2 to 4 times more likely to be classified as having severe damage than those with column indices exceeding 0.2% for ground motions with PGVs between 40 cm/s and 120 cm/s. The prior building surveys supported these observations