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ST7-1.10.20.22 Compression-Only Footfall Harmonic Response Analysis
Footfall analysis on pedestrian-loaded structures is often performed using the Harmonic Response solver, which is used to determine the steady-state response of a structure to a given sinusoidal forcing load. Whilst it is tempting to simply apply the peak footfall load in such an analysis, this approach assumes that the footfall load acts in tension as well as compression, when in reality the step load is more like a half-sine wave.
The assumption that the load acts in both tension and compression is not necessarily a conservative one. There is more to the difference between a half-sine wave and a fully-reversing sine wave than the load magnitude. Whenever a discontinuous acceleration is applied, it can excite higher frequency modes than the frequency of the applied footfall load. Thus the footfall, while nominally acting around 2.0 Hz, can also excite natural frequencies with harmonics around 4.0 Hz, 6.0 Hz, 8.0 Hz, 10 Hz etc. (n x fstep).
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