The steel-concrete constructions experience an increased development this last time. The main advantages are that they ensure the economy of materials, energy and labour. The steel-concrete elements allow a rational use of the concrete in the tensile zone, ensure a reduction of the weight of the building, its cost and also reduce the formwork. The calculations carried out by the authors make it possible to establish the dependence between the constraints and the deformations in the principal directions under a biaxial state of stresses, to obtain the expressions of the principal moments, determine the parameters of the deformations of the concrete E_b, E_bi, ν_b, ν_bi, obtained through the reduction of the tensile and compressive stresses of the concrete in an isotropic conventional homogeneous state. The expressions of the constraints in the plate are gotten and compared between the theoretical values and the experimental convergence of the results with a variation of less than 8%.