The forthcoming revision of Eurocode 5 (EN 1995-1-1) introduces a substantially expanded section on timber floor vibrations (Clause 9.3), representing the most comprehensive guidance to date within the Eurocode framework. This development is of significant value, considering the increasing relevance of human-induced vibrations in modern timber construction.
This paper provides a critical appraisal of the new provisions, structured according to three categories: Positive developments (The Good), identified limitations (The Bad), and more fundamental shortcomings (The Ugly).
The Good: Velocity Criteria
- Velocity criteria for transient response (typically f₁ ≥ 8 Hz)
The proposed root mean square (RMS) velocity limits for transient timber floor vibrations are generally well aligned with empirical observations and established comfort thresholds. These values offer a practical and reliable design basis, particularly for lightweight floor systems where the risk of resonance is negligible. - Simplified frequency estimation
The inclusion of a closed-form expression for estimating the fundamental frequency of floors supported on elastic boundaries (Formula 9.16) provides a direct and usable tool for preliminary assessment. While limited to relatively simple configurations, the formula enhances accessibility and consistency in early-stage design.
The Bad: Acceleration model
A key concern relates to the methodology for estimating floor accelerations under resonant excitation (typically f₁ < 8 Hz). Specifically:
- The suggested resonant build-up factor (μₐ = 0.4) significantly reduces the estimated acceleration response. This value is considerably lower than what has been reported in established sources, such as SCI P354, where values typically are above 0.85 [1].
In Danish practice, it is customary to design for a single pedestrian and not to include reduction factors related to the duration of the load or resonance build-up, BEF. This conservative approach implicitly accounts for the possibility of multiple people walking simultaneously. The combined use of μₐ = 0.4 and damping-based reductions in EN 1995-1-1 will most likely lead to non-conservative assessments of accelerations.
The Ugly: Acceleration criteria
Several issues merit more fundamental critique:
- The acceleration criteria across comfort classes are relatively permissive, corresponding to high response factors (e.g., R = 16 for level IV), which is expected to be insufficient to ensure user comfort in residential or office applications for natural frequencies below 8 Hz.
More critically, the proposed methodology is inherently biased toward high-frequency floor systems. As acknowledged in the background documentation:
“Most of the existing test data on the vibration performance of timber floors is for the transient floor type […] For resonant floors […] there is not as much experience in timber construction […].”
This limitation is particularly relevant in the context of timber-concrete composite systems, which are often used to satisfy both acoustic and vibration requirements in practice. These systems are typically heavier and may exhibit resonant behaviour not adequately covered by the current provisions.
Conclusion
There is a high risk that vibration issues will be underestimated in design—particularly for resonant timber floors classified as comfort class III or higher—if the current acceleration model and comfort class scheme are applied without adjustment.
While the vibration guidance in EN 1995-1-1 marks a substantial step forward, introducing comfort classes, quantitative limits and analytical tools, the reliability of the proposed acceleration model and the practical relevance of the classification scheme remain open to question.
To ensure robust performance and user comfort, further calibration against empirical data, national adaptation, and alignment with established international methods is strongly recommended.
If you have questions or want to discuss a specific project, feel free to contact me directly at jsk@jsk-vibrations.com.
For a detailed discussion of transient floor vibrations and real-world user complaints, see:
https://jsk-vibrations.com/transiente-svingninger-og-brugerklager/
References
[1]: M. Roywaran, O. Avci and B. Davis, “Analysis of floor vibration evaluation methods using a large database of floors”, 2019