Amplitude scaling of ground motions as a potential source of bias: Large‐scale investigations on structural drifts

Abstract

The question of whether amplitude scaling of ground motion (GM) records introduces bias is controversial in earthquake engineering. In this study, this research question is formally defined with a focus on evaluating bias in determining an engineering demand parameter (EDP) as a result of nonlinear response history analyses (NLRHA) when using scaled rather than unscaled GM that have the same level of intensity. The analysed structures are 10 planar steel frame buildings ranging from low-to high-rise, where the EDP of interest is the maximum interstory drift ratio, while the structural responses range from linear to collapse. A unique contribution is the depth of the research, which employs an unprecedented number of more than 17,000 recorded GM, resulting in approximately 3.4 million NLRHA. For a thorough investigation, the most relevant intensity measures are discussed and considered, as well as novel spectral information describing the sustained vibration amplitude. The introduction of bias is examined from different points of view, using first simple and intuitive statistical methods, then machine learning techniques, and finally a novel GM selection approach. In the numerous investigations, no bias could be detected under the inherent uncertainty of the calculations. The results indicate that scaled records can be safely used in NLRHA to assess the seismic structural behaviour if spectral and scenario compatibility are ensured and it is verified that the sustained amplitude is also consistent.

A closer look at hazard-consistent ground motion record selection for building-specific risk assessment: Effect of soil characteristics and accelerograms’ scaling

“…They anticipated that this bias might be avoided once the spectral shape is accounted for within the record selection. Indeed, this proposal was later confirmed by several studies (Baker, 2007; Tsalouchidis and Adam, 2022). In contrast to those studies, Dávalos and Miranda (2019) showed that scaling the ground motions can induce bias in the median displacement demands and collapse probability estimates, even if they used CMS for their record selection.…”

Erratum: Amplitude scaling of ground motions as a potential source of bias: Large scale investigations on structural drifts

“…In the original publication, 1 Figure 2c contains the 50th percentile spectrum of the ground motion CHICHI.02‐TCU105N instead of the 80th (as it should). The correct figure is shown here (together with the remaining sub‐figures of Figure 2 for completion).…”

Which Significant Duration of Ground Motions to Use? Investigations on Artificial Neural Networks Predicting Building Seismic Collapse

“…For each NLRHA, the scale factor was stored, an indication of whether a collapse occurred, and the displacements, drifts and accelerations of each story / floor were monitored as the engineering demand parameters (EDP) of interest. It should be noted that in this study, collapse was identified when an MIDR value greater than 0.1 was reached, which is a commonly considered a threshold [31,28]. The EDP values to be stored were selected at the time instances of excitation when a peak EDP of each story / floor occurred, as well as residual values.…”

“…In this way, the significant durations remain the same for any amplitude-scaled version of the GM, whereas the time-occurrence of structural responses of interest is likely to be amplitude-dependent. Amplitude scaling is widely utilized in the literature [28], for example, in IDA where amplitude scaling is performed until the collapse limit state is reached. Therefore, the above question also needs to examine the ability of Ds 5−75 or Ds 5−95 (or any other significant duration metric) to describe the part of the GM that is significant for the various (relevant) amplitude-scaling versions of the GM.…”