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CCEER-20-07: Regional-Scale Seismic Risk To Reinforced Concrete Buildings Based On Physics-based Earthquake Ground Motion Simulations
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This document reports the development and findings of a computational study which examines the regional-scale variability of seismic risk to reinforced concrete (RC) buildings using physics- based earthquake simulations. The development of the structural simulation models is presented first, followed by a description of the study components, and discussion of its findings as they relate to the seismic risk to RC buildings. Finally, the implications of the study findings on the performance and design of RC buildings near active earthquake faults are summarized, and the study limitations are reported. This report is divided into three parts: In part I, the simulation framework for RC moment frames is described. The framework rests upon the theory of lumped plasticity (LP) models, which is described in the first chapter. The second chapter outlines a program, the RC Structural Model Generator, which calibrates the LP component parameters and generates structural analysis scripts of RC frames with any number of stories/bays. The program is intergated into a regional-scale workflow to allow for expedient simulation of the nonlinear response of RC buildings to earthquake ground motions over large computational domains. The program performance is assessed using several static and dynamic verification problems that are described in the following chapter. In part II, broadband physics-based earthquake simulations are utilized to characterize the regional-scale risk to modern RC buildings using the workflow described in part I. Dense datasets of high-resolution simulated ground motions were generated using kinematic fault rupture mod- els with varying rupture characteristics to represent shallow crustal earthquakes, and resolved up to frequencies of 5 Hz. Over forty thousand nonlinear time history simulations of modern short- and mid-rise RC special moment frame buildings were conducted. The spatial variability of the structural risk within a single earthquake scenario and between different rupture scenarios was examined, and the impact of the geologic and rupture characteristics on the structural response quantities was characterized. In addition, the relationship between the structural demands near the fault and the stiffness and ductility characteristics of the buildings was investigated. The study reveals that the structural demands on RC buildings due to a M7 strike-slip earthquake may vary by a factor of up to 8.0 at very short distances from the fault, and the dispersion in the demands is found to depend on the frequency content of the buildings. The interstory drift and member rotation demands are substantially impacted by important features of the geological structure and the characteristics of the rupture scenarios, particularly the presence of localized high-slip regions along the fault plane. Flexible buildings exhibit higher sensitivity to the presence of strong veloc- ity pulses near the fault, as compared to stiffer buildings. Comparison of the characteristics of the simulated ground motions against real earthquake records suggests that the simulated motions, par- ticularly using the hybrid rupture scenarios, may offer reasonable risk estimates for low-frequency structures, and conservative estimates for high-frequency structures. Part III of this report presents some computational and theoretical supplements to the study, including the software tool which was created to aid the design of modern RC moment frame buildings.
Report No. CCEER 20-07