The research, led by Tao Wang of Heilongjiang University of Science and Technology and Guoshan Xu of Harbin Institute of Technology, together with Rui Pan, Liyan Meng and Jisheng Liu, introduces a novel quantitative method for analyzing the floor acceleration amplification (FAA) factor based on actual recorded earthquake response data from instrumented buildings. Rather than relying on the numerical simulations that have dominated the field, the team mined the archives of the Center for Engineering Strong Motion Data (CESMD), extracting recorded building responses that capture how structures genuinely behave when the ground moves beneath them.

The core problem the researchers set out to solve is well known in earthquake engineering circles. “The existing literature on FAA did not analyze various influencing factors quantitatively,” the authors note in their abstract. Design codes around the world — including ASCE 7 in the United States, Eurocode 8 in Europe, New Zealand’s NZS 1170.5 and China’s GB 50011 — contain provisions for computing seismic design forces on nonstructural components, and most of them lean heavily on a single variable: the height of the component within the building. The implicit assumption is that the higher you go, the more the acceleration is amplified, with the relationship varying according to the structural system. But how much do other factors — the soil beneath the building, the building’s height, its fundamental period, the intensity of the ground motion itself — actually matter? Previous work had hinted at their significance, but rarely in quantitative terms grounded in field data.

The new method treats the FAA factor as a multi-variable statistical problem. For each instrumented building and recorded event, the researchers characterized six influencing factors: structural type, structural height, site category, structural period, relative height (the component’s elevation expressed as a fraction of total building height) and ground motion intensity. They then computed FAA values from the recorded peak floor accelerations and peak ground accelerations, and applied formal correlation analysis to determine which of these factors were genuinely and strongly associated with amplification behavior — and which could be safely neglected or, conversely, demanded explicit inclusion in design formulations.

The results are striking in at least one respect that the authors say has been underappreciated. Site category — the classification of the soil or rock beneath a building, which governs how ground motion characteristics are modified before reaching the foundation — was found to significantly affect FAA values across different types of structures. “The site categories can significantly affect the FAA values of various types of structures,” the study reports, adding that this influence “has not been emphasized in previous studies.” In practical terms, this means that two structurally identical buildings on different soil conditions may subject their rooftop equipment to markedly different acceleration demands during the same earthquake — a distinction that current code formulas for nonstructural components largely fail to capture in a refined way.

The correlation analysis also delivered a clear verdict on relative height. This factor, the study confirms, is strongly correlated with FAA, a finding consistent with the structure of several seismic design codes that scale nonstructural design forces with elevation. In other words, the codes’ long-standing intuition that amplification grows with height holds up under scrutiny with real data. But the analysis went further, revealing that three additional parameters — site category, structural height and structural type — are also significantly correlated with the FAA factor. On the strength of this evidence, the authors argue that these three factors should be incorporated into seismic design codes for acceleration-sensitive nonstructural components, a recommendation that, if adopted, would represent a meaningful refinement of the simplified equations engineers currently use.

The technical significance of the work lies partly in its grounding in instrumented buildings. Numerical models, however sophisticated, embed assumptions about damping, stiffness distribution, and inelastic behavior that may or may not reflect reality. Records from buildings during actual earthquakes — the kind curated by CESMD — carry no such assumptions. They are the ground truth of structural dynamics, capturing everything from soil-structure interaction to the softening effects of yielding that influence how accelerations propagate upward. By quantifying FAA influencing factors directly from such records, the method sidesteps a major source of modeling uncertainty, though it also inherits the practical constraints of any observational dataset: the available buildings, sites and shaking intensities are those that earthquakes happened to provide.

Why does this matter beyond the technical literature? Post-earthquake damage surveys have repeatedly shown that nonstructural components account for a large share of earthquake losses, both direct and indirect. Investigations after the 2010 Chile earthquake, the 2011 Christchurch earthquake and the 2016 Central Italy earthquake documented widespread failures of ceilings, facades, pipes and equipment, often in buildings whose primary structures performed well. Failed fire suppression lines can render a fire-fighting system useless precisely when it is needed; toppled switchgear can knock a hospital out of operation even if the building stands. Accurately predicting the acceleration that such components will experience — which is precisely what the FAA factor enables — is therefore central to estimating their seismic safety and to the broader goal of resilient, functional cities.

The study’s authors frame their contribution as offering “valuable insights and recommendations for the design of acceleration-sensitive nonstructural components in terms of FAA.” The quantitative method they propose gives code developers and practicing engineers a data-backed way to weigh the competing influences on floor acceleration demands, rather than relying on convention or on idealized simulations. It also provides a template for future studies: as seismic instrument arrays expand and more instrumented buildings record more events, the same statistical framework can be applied to ever-larger datasets, potentially refining amplification models region by region and structure type by structure type.

There are, of course, limitations inherent in any data-driven approach, and the researchers’ recommendation to add site category, structural height and structural type to code formulations will require careful implementation. Design equations must remain tractable; adding variables increases both computational burden and the potential for misclassification in practice. But the study’s central message is hard to dismiss: the acceleration that shakes a component on the tenth floor is not determined by height alone, and the ground beneath the building — the very first link in the chain of seismic response — deserves a more prominent place in how engineers compute nonstructural design forces.

The research was supported by the National Natural Science Foundation of China under grants 52278173, 52378150 and 52078398, and by the Foundation of the Key Laboratory of Structures Dynamic Behavior and Control (Ministry of Education) at Harbin Institute of Technology. Corresponding author Guoshan Xu led the collaboration spanning Heilongjiang University of Science and Technology and Harbin Institute of Technology, institutions at the heart of China’s earthquake engineering research community. As cities grow taller and their contents grow more technologically sensitive — data centers, laboratories, hospitals dense with equipment — the question of what accelerations those contents will feel in the next major earthquake is only becoming more consequential. This study offers a rigorous, record-based answer to part of that question, and a clear signal about where design codes should go next.