Simply supported rectangular thin plates under transversal load, concentrated at the centre of the plate, can show a particular kind of instability at one or two edges depending on their dimensions. If only small displacements are considered, the problem is one of pure bending and instability does not occur; on the contrary this instability is induced by the compressive membrane stresses due to large displacements. Vitreous enamel coatings, generally used to improve anti corrosion properties, increment the load value required to induce the instability by inducing residual tensile stresses on the plate. This paper compares and discusses experimental tests on steel and enamelled steel plates and the results obtained by a non linear numerical model taking into account residual stresses. By both experimental and numerical analysis it was possible to conclude that the presence of residual stresses caused an increment of the values of force and work at which the instability took place with respect to the case where residual stresses were not present.
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