I am designing a steel dump hopper / bin for an iron ore crushing plant. The hopper accepts 240 Tonne truck loads of iron ore with a maximum lump mass of 4.7 t. The bin will be constructed from steel plate which is stiffened vertically and horizontally. The horizontal stiffeners are the main stiffners to the bin and have varying spans. The shell is protected with internal liner plates and impact rails. The ore free falls from the skip of the truck and impacts on the sloping walls of the bin before landing on an apron feeder. I am trying to size up the stiffeners for the bin for the impact loads associated with the free falling ore. To date I have used a conservation of energy approach ie equating the kinetic energy of the falling 4.7 t rock to the internal strain energy of the deflected horizontal stiffener. The formula I have used to calculate the impact force is F = W x Vn x SQR ( K / g( W + We)). Where W = weight of rock, Vn = velocity of rock normal to stiffener, K = flexural stiffness for stiffener, We = weight of stiffener. The problem that I have at the moment is that the impact loads are around the order of 1000kN and the stiffener sizes are becoming quite large even with the use of a 0.9 x yield stress as an allowable.Does this seem like a reasonable approach to take ?
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