300 P.J. Fanning and A. Devin Fig. 30.4 Finite element meshes without (on left) and with (on right) partitions Fig. 30.5 Displacement responses on levels 1 and 2 due to pedestrian walking Table 30.1 Peak floor level accelerations due to walking Model Floor level 1 (mm 103/s2) Floor level 2 (mm 103/s2) Transmission ratio (%) With partitions 99.1 8.9 9.0 Without partitions 163.7 3.0 1.8 For the purposes of considering vibration transmission the responses at a point mid-way along the walking trajectory and at a point located immediately above this, on floor level two, were considered. A transient dynamic analysis was performed using a time step of approximately 0.015 s so as to adequately capture the load dependency on the pacing frequency of 1.8 Hz. The analysis duration was 7 s. For each time step the force exerted and position along the walking path was determined. The load was then shared pro-rata to the two closest node points along the path and ramped from prior values. Because of the un-even nature of the mesh (node to node distances were nominally 0.4 m but not exactly 0.4 m) this led to a unsteady high frequency content in the acceleration response which made direct comparison of effects difficult using acceleration responses—displacement responses, at the two reference points, were thus employed for evaluating comparative accelerations. These displacement (in the vertical direction) responses are plotted in Fig. 30.5. The response at each reference point is an oscillatory response at 1.8 Hz due to the walking load model pacing frequency applied. The peak acceleration at the reference point occurs when the load is at the reference point and is determined from the maximum peak to peak deflection divided by two and multiplied by the response frequency squared in radians per second. The peak accelerations, so calculated, are listed in Table 30.1.
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