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Over the next few months we’ll be taking a look at the extra knowledge our Engineers have gained through working on some of our high profile projects. This month Director James Hill talks about an objects behaviour during an earthquake.

‘This month I’ve been learning about predicting how an object that isn’t tied down will react during an earthquake.  I’ve been interested in knowing how much it might slide, as well as rock and predicting these numbers to make sure the object won’t fall over.  I’ve been using ASCE 43-05 Design Requirements for Nuclear Facilities.  The interesting part about this has been looking at the theory behind it and how this interacts with a seismic event.

When an object rocks, its frequency changes depending on how far it has tilted.  This creates a variable frequency oscillator that constantly adjusts its response.  This is completely different to a fixed structure which will have a series of fixed modal frequencies that can easily be found.  However, with some simple assumptions it is possible to calculate a maximum rocking angle and therefore make sure it doesn’t fall over.  The best part about this work is that it is an effect you can see everyday very easily by tipping an empty cup and watching it change how quickly it rocks at the start compared to when it just finishes.’

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