Vibration of Floors (SCI-P-354): Comparing response factors

The most significant changes in P354 are in

1. The evaluation of modal mass
2. The ability to use VDV analysis to justify floor systems which fail analysis

P354 gives results that seem to be more conservative but more consistent primarily due to the fact that the step changes in the calculation of the modal mass have been smoothed out and the massive differences across the boundary conditions returned by P076 are no longer apparent.

For P076 Cases 1 & 2 (secondary mode)

Long span secondary beams and shorter span primary beams means that the secondary beam mode deflection governs the floor behaviour:

Case 1: P354 returns more conservative results

Case 2: The Step change prompted by the inequality 0.8 > I/L < 0.8 does not exist in P354 and there is a smooth transition across the boundary

For P076 Cases 3 & 4 (primary mode)

Long span primary beams and shorter span secondary beams means that the primary beam mode deflections governs the floor behaviour:

Case 3: P354 returns more conservative results

Case 4: The Step change prompted by the inequality 0.8 > I/L < 0.8 does not exist in P354 and there is a smooth transition across the boundary

Vibration Dose Values (VDV) P354 Section 6.6

If the calculated response values are within the limits of the multiplying factors for the continuous vibrations, there is no need to consider the intermittent nature of the dynamic forces.  However, for the situation where the floor has a higher response than would be acceptable under the conservative limits for continuous vibration, and design specification permits the use of VDV, the acceptability may be assessed by considering the intermittent nature of the dynamic forces.  A VDV analysis is effectively allowing the response to be greater than those specified for continuous vibrations, but only for small periods of time.