No abstract

The Next Generation Attenuation (NGA) relationships for shallow crustal earthquakes in the western United States predict a rotated geometric mean of horizontal spectral demand, termed GMRotI50, and not maximum spectral demand. Differences between strike-normal, strike-parallel, geometric-mean, and maximum spectral demands in the near-fault region are investigated using 147 pairs of records selected from the NGA strong motion database. The selected records are for earthquakes with moment magnitude greater than 6.5 and for closest site-to-fault distance less than 15 km. Ratios of maximum spectral demand to NGA-predicted GMRotI50 for each pair of ground motions are presented. The ratio shows a clear dependence on period and the Somerville directivity parameters. Maximum demands can substantially exceed NGA-predicted GMRotI50 demands in the near-fault region, which has significant implications for seismic design, seismic performance assessment, and the next-generation seismic design maps. Strike-normal spectral demands are a significantly unconservative surrogate for maximum spectral demands for closest distance greater than 3 to 5 km. Scale factors that transform NGA-predicted GMRotI50 to a maximum spectral demand in the near-fault region are proposed.

No abstract

A blast assessment of a sample power reactor building is performed for an assumed threat of 2000 kg of TNT explosive detonated on hard rock at a standoff distance to the reactor building of 10 m. The air- and ground-shock waves produced by the design threat are generated and used for performance assessment. The air-blast loading on the sample reactor building is computed using a Computational Fluid Dynamics code, Air3D, and the ground-shock time series is generated using an attenuation model for rock response. Response-history analysis of the sample conventional and base-isolated reactor buildings to external blast loadings is performed using LS-DYNA. The structural responses, including acceleration, drift and peak floor acceleration demands on key secondary systems attached to the internal structure of the reactor building are identified for both the conventional and base-isolated sample reactor buildings. The results show the installation of a base isolation system does not increase the vulnerability of either the containment vessel or internal structure to air-blast loading and reduces the ground-shock response by orders of magnitude.

No abstract