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 Ian Hylands talks about impact analysis.

“Recently Eadon were asked to provide substantiation for a floor structure in a nuclear facility.  The floor was mechanised to allow it to retract, facilitating access to a maintenance pit below.  The floor needed to be able to withstand an impact from a heavy object without allowing it to penetrate, in order to protect against a nuclear hazard.  Unfortunately, the object was falling from high enough that it was not practical to design the floor using traditional design codes.  Strengthening the floor to take the loads would, in turn, stiffen it and increase the loads further, leading to a vicious circle resulting in the floor being way too heavy to move.”

“To get around this problem, we needed to use the ability of the structure to yield and absorb impact energy through plasticity.  A finite element analysis was prepared with ANSYS Workbench, and a non-linear material was used to represent the stress-strain curve of the structural steelwork.  An energy-based approach was then used, equating the gravitational potential energy of the object before it fell with the total elastic and plastic strain energy in the finite element model when a deflection was applied at credible impact locations.  The resulting stresses and strains could then be assessed to ensure that while the material was able to yield, it did not result in failure.  This approach allowed a practical moving floor design to be adopted while still fulfilling the demanding nuclear safety requirements imposed on it.”

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