Uncertainty in the seismic response of reinforced concrete structures due to material variability

Inherent variability in the mechanical properties of reinforcing steel and concrete introduces uncertainty into the seismic assessment of reinforced concrete structures. Due to the high level of uncertainty associated with earthquake shaking characteristics, uncertainty due to variability in material properties is typically disregarded for seismic assessments. However, the potential impact of incorporating multiple sources of uncertainty in the seismic assessment framework is not well understood. To quantify the impact of material uncertainty, one-hundred iterations of a numerical model of a reinforced concrete structure are evaluated for their seismic performance at several earthquake shaking intensity levels. The one-hundred models differ only by the constitutive parameters used to model the materials, which are selected in accordance with measured statistical distributions of the mechanical properties of reinforcing steel bars and concrete. Material property statistical distributions, and correlations between material properties, are established using test data collected by the authors and test data available in the scientific literature. Preliminary results from analyses at the component level (i.e., individual column) indicate that dispersion in the predicted drift response for a given ground shaking intensity (Sa[T1]) generally increases with shaking intensity, especially in the post-peak response regime for which a coefficient of variation (COV) in excess of 30 % is observed in the analyses presented herein. Of particular interest is the fact that a COV up to 20 % is observed for ground shaking intensities that produce only moderate ductility demands, prior to the onset of strength loss.