COMFORT IN VIBRATIONS FOR THE STEEL-CONCRETE COMPOSITE FLOORS: AN APPRAISAL FOR REVIEW OF ABNT NBR 8800:2008

Resumo

Steel-concrete composite floors often have human comfort for excessive vibrations as the
most critical Service Limit State, in which vibration-sensitive floor systems must be designed so as to
avoid the unacceptable transient oscillations due to the walking of people or due to other sources.
According to ABNT NBR 8800:2008 [1], this limit state is designed by controlling the natural
frequency of the floor under service loads, keeping it above a certain threshold, generally from 3.0Hz
to 4.0Hz for the most common cases according to its Annex "L". The main objective of this article is
to propose a bibliographic review on the evaluation of comfort for floors, based on their dynamic
characteristics, such as natural frequency (f), modal mass (Mmod) and damping (D) to obtain speed
values (OS-RMS90) and acceleration (peak), when applying dynamic loads as predicted by Sedlacek
[2]. The object of study is a steel-concrete composite slab of a steel construction at the Federal
University of Espírito Santo (UFES, Brazil). After analytical calculations and numerical modeling
with dynamic loads, the floor is instrumented and kinematic results (velocity and acceleration) are
compared between model and experiment. By means of spectral analyzes of vibration energy, stiffness
gains by concrete ageing are observed for calibration of the model, accordingly to Ji Young Kim [3].
Finally, the answers of a questionnaire about comfort answered by the occupants are discussed and
compared with international publications to integrate new comfort thresholds and analysis
methodology in the new related chapter of ABNT NBR 8800:2008, currently under review.