Probabilistic Assessment of Non-Ductile Reinforced Concrete Frames Susceptible to Mid-America Ground Motions
Celik, Ozan Cem
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The infrequent nature of earthquakes in the Central and Eastern United States (CEUS), and the fact that none with intensity comparable to the New Madrid sequence of 1811 12 or the Charleston earthquake of 1886 has occurred in the past century, have caused the earthquake hazard in the region to be ignored until quite recently. The seismic performance of reinforced concrete (RC) frames in the CEUS, which have primarily been designed for gravity load effects, is expected to be deficient when subjected to earthquakes that are judged, in recent seismological research, as being plausible in the New Madrid Seismic Zone (NMSZ). The objective of this study is to develop a set of probability-based tools for efficient uncertainty analysis and seismic vulnerability and risk assessment of such gravity load designed (GLD) RC frames and to use these tools in evaluating the seismic vulnerability of RC frames that are representative of the building inventory in Memphis, TN the largest population center close to the NMSZ. Synthetic earthquake ground motions for the CEUS that are available from two different Mid-America Earthquake (MAE) Center projects were used in the finite element-based simulations for determining the seismic demand on the GLD RC frames by nonlinear time history analysis (NTHA). A beam-column joint model was developed to address the deficiencies in the joints of GLD frames and was incorporated in the finite element structural models. Seismic fragilities were derived for low-, mid-, and high-rise GLD RC frames. Various sources of uncertainty were propagated through the analysis, and their significance for fragility assessment was examined. These fragilities were used to evaluate the vulnerability of the RC frame inventory in Memphis, TN with regard to performance-based design objectives, defined in terms of performance levels associated with reference earthquake hazard levels. This performance appraisal indicated that GLD RC frames do not meet the life safety and collapse prevention performance objectives that are found in recent building codes and guidelines for performance-based earthquake engineering.