For calculation of critical load of the structure, user has to enter the following data: the length a of the plate in the x-axis direction, the length b of the plate in the y-axis direction, thickness of the plate h, which is constant in both directions, and material properties. It is assumed that the material of the shell is orthotropic with the elastic stress-strain relationship:
User has to enter the moduli of elasticity Ex and Ey of the material in x-axis and y-axis directions, shear modulus Gxy , as well as Poissonís ratio νyx. The second Poissonís ratio is calculated using formula νxyyxEx / Ey. We also check the restriction νxyνyx < 1 for orthotropic material and 0≤ νxy ≤ 0.5 for isotropic material before the calculation. In the case of isotropic material the field for shear modulus can be left blank. Corresponding value will be calculated by formula Gxy=Ex /(1+ νyx)/2 .

Please use the same system of units throughout the calculation. For instance, if you use force unit N and length unit m, the unit of elasticity modulus should be N/m2. Obviously, the result of calculation will have the same unit system in this case: uniformly distributed load Ė N/m.

The program calculates the critical value of load combination, which is represented both graphically and by formulas.