Perceptibility
Either of the two methods may be used to determine the perceptibility of vibration in the floor system, and for either method the effects of the supporting girders may be either considered or ignored. Engineering judgment should be used when determining which methodology to employ.
In Method 1, RAM Steel Beam Design determines the location of the point on the Modified Reiher‑Meister scale based on the calculated value of the first natural frequency and the amplitude of vibration, and informs the user of the vibration perceptibility of the beam. The Slightly Perceptible and Distinctly Perceptible regions are further partitioned into lower half and upper half to give the user a better idea about the location of a point in these regions. Reference 1 (p. 83) gives the following recommendation:
From measurements and subjective evaluations obtained by the author, it has been found that steel beam‑concrete slab systems, with relatively open areas free of partitions and damping between 4 and 10%, which plot above the upper one‑half of the distinctly perceptible range, will result in complaints from the occupants and that systems that plot in the strongly perceptible range will be unacceptable to both occupants and owners.
The Modified Reiher‑Meister scale is shown in Figure 1 of Reference 1.
| D > 35 A0f + 2.5 |
| = | ||
| = | ||
| = |
A0 and f are calculated as explained above; the actual available damping, D, must be determined by the engineer. If sufficient damping is available in the floor system (from partitions, ceilings, slab, etc.), floor vibration will not be a problem. Reference 3 (p103) states:
The recommended criterion states that if the... inequality is satisfied, motion of the floor system caused by normal human activity in office or residential environments will not be objectionable to the occupants....
Use of this criterion requires careful judgment on the part of the designer. A light office building floor system with hung ceiling and minimal mechanical ductwork will exhibit at least 3‑3.5% of critical damping. Additional damping may be provided by a thicker slab, office furniture, partitions, equipment, and the occupants themselves. If the required damping is less than 3.5‑4%, the system will be satisfactory even if the supported areas are completely free of fixed partitions. If the required damping is between 4% and about 5%, the designer must carefully consider the final configuration of the environment and the intended use... If the required damping is much greater than 5%, the designer must be able to identify an exact source of damping or artificially provide additional damping to be sure the floor system will be satisfactory. If this cannot be accomplished, redesign is necessary.
See Reference 3 for a discussion on determining the actual damping in a floor system, as well as additional caveats.
If the two methods result in conflicting perceptibility ratings, it seems reasonable to assume that except in extreme cases, Method 2 should take precedence since that method represents the more recent research by T. M. Murray.