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Nothing new in reducing the bounce

I read your article on the GSA Footfall software with interest but stopped short of finding it 'revolutionary' (NCE last week).

There are many existing software packages that calculate the accelerations produced by defined pedestrian loadings; they just don't try to define the loadings to apply or the tolerable accelerations because there are no universally accepted or codified values.

In particular, reference has to be made to a variety of technical papers to inform the choice of appropriate comfort criteria, which are quite personal.

In the design of our footbridges, design cases are considered for different numbers of pedestrians, runners and vandals all exciting the bridge in the course of their particular business.

The selected comfort criteria need to fit the relevant scenario.

Where excessive vibration is predicted, tuned mass dampers are one possible means of rectification to be added at likely locations if necessary.

But no matter how clever the software, the all-important material stiffnesses, and hence natural frequencies, cannot usually be predicted with great precision. Some form of site testing is therefore required.

This facilitates both tuning of the tuned mass dampers predicted to be necessary by the design, but also location and installation of any further dampers that might be necessary.

CHRIS HENDY (F),
Chris.Hendy@atkinsglobal.com

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