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Floor vibration (SCI P354) ​

Tools ▸ Floor vibration (P354)… assesses a floor's response to walking by the general (finite element) method of SCI P354 Design of Floors for Vibration: A New Approach, on the modal analysis already on screen. Run a Modal analysis first (Analysis type ▸ Modal, with enough modes to reach the Table 6.1 cut-off plus 2 Hz); the dialog reads the frequencies, the mode shapes and the modal mass of each mode.

What it computes ​

  1. Modal mass. The eigen solver returns, for every mode, the modal mass of the unity-normalised shape (largest nodal translation 1), which is P354's Mn (Equation 10). The publication's own check, "a simply supported beam's modal masses are half its mass", is a test in the suite.
  2. Floor class by Table 6.1: low-frequency below 10 Hz for general floors and open-plan offices, 8 Hz for enclosed spaces (residential, operating theatres), 12 Hz for staircases.
  3. Steady-state response (low-frequency floors, Section 6.3.2): for each mode up to the cut-off plus 2 Hz and each of the four walking harmonics of Table 3.1, Equation (29) a = μe μr (Fh / Mn) Dn,h Wh / √2, summed by SRSS (Equation 36), at every pace frequency from 1.8 to 2.2 Hz (Equation 14). A walking path length applies the Equation (37) build-up factor.
  4. Transient response (every floor, Section 6.3.3): for each mode up to twice the fundamental, Equation (33) with the Equation (18) heel impulse, summed over one pace period (Equation 34) and reduced to an rms (Equation 12).
  5. Weighting by the BS 6841 curves of Equations (21) to (23): Wb for discomfort (offices, residential, wards), Wg for vision and hand control (operating theatres, precision laboratories); Table 5.1 says which.
  6. Response factor R = a_w,rms / 0.005 (Equation 38), compared with the multiplying factor of Table 5.2 (BS 6472) or Table 5.3 (SCI's recommended values: offices 8). The panel plots R against pace frequency for both responses with the limit as a rule.

The excitation and response nodes default to where the fundamental mode moves most vertically, which is the conservative choice of Section 6.3.4; tick μe = μr = 1 to take the shape amplitudes as unity everywhere. Damping comes from Table 4.1 (0.5 % welded steel, 1.1 % bare, 3.0 % furnished, 4.5 % with partitions interrupting the mode).

Every constant is read from the publication and held against the compiled engine by a ledger check (docs/reference/p354_validation.md).

From a script ​

js
// after a modal solve
CivilKit.floorVibration({ damping: 'furnished', weighting: 'Wb', floor: 'general', limit: 8 });
// { response_factor, governing, governing_pace_hz, floor_class, steady_state, transient, warnings, ... }

excitationNode and responseNode take the solver's node numbers; unitShape: true sets every amplitude to 1; walkingPath (m) applies the build-up factor.

Not carried ​

Vibration dose values (Section 6.6), rhythmic crowd loading (Table 3.3), staircase coefficients (Table 3.2), the simplified method of Section 7, AISC Design Guide 11 and CCIP-016. The engine says so in its warnings.