In this paper we propose a second order method to analyse concrete frames based on the imposed deformations method. The geometrical nonlinearity is introduced by using imposed curvatures associated to the "second order isostatic forces" defined in this paper. In the same way material nonlinearity is introduced by means of imposed curvatures obtained from the axial rorce-moment-curvature diagram of each cross section by compatibility of material properties requirements. The proposed nethod can be considered to fall within the "General method" proposed by the C.E.B. Several structures are analysed comparing the results with those obtained by other dnalytical methods and conclusions are drown both relative to the method's proper ties and the structural behaviour.

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