Seismic Input Minimum Power Spectral Density Compliance Effect on In-Structure Response Spectra

Abstract This article explores the impact of using spectrally matched acceleration records on the generation of in-structure response spectra (ISRS), with a focus on the U.S. Nuclear Regulatory Commission (US-NRC) Standard Review Plan (SRP) Revision 4, section 3.7.1, and its acceptance criteria for response spectrum-matched input time histories. These criteria include checks for how well the response spectrum matches the target spectrum and for a minimum power spectral density (PSD) distribution. While both criteria are addressed in ASCE/SEI 4-16 and ASCE/SEI 43-19, the PSD check is only required if the motion or suite mean response spectrum exceeds the target by more than 30% at any frequency in the range of interest. This scenario is uncommon due to advances in spectral matching methods that enable a tight match of the target design response spectrum. In this study, two sets of spectrally matched records were constructed. The first set adhered to the target response spectrum matching criteria and was generated by modifying historical records using a Continuous Wavelet Transform (CWT) technique. The second set included additional CWT modifications to ensure compliance with the minimum PSD criterion. The findings show that meeting the response spectral matching criterion does not automatically ensure compliance with the minimum PSD requirement. PSD compliance was found to significantly affect individual record responses and the mean ISRS, particularly when using smaller record sets. Achieving a conservative mean ISRS with 90% confidence required more records than commonly used in practice (4–5 records). Specifically, for records meeting only the response spectrum matching criterion, at least 11 records were necessary, whereas PSD-adjusted records required a minimum of 7 records.