A new equation for the modelling of the shearing process of a bolted rock joint is presented in this paper. The complete curve of the bolt contribution to the shear strength as a function of the displacement along the joint is described by a power function. The determination of the required parameters needs to know the bolt contributions and the corresponding displacements at both the yield and the failure limits of the bolt. These parameters are computed based on an analytical model developped for a sliding along the joint. The main characteristic of this model is the account of the interaction of the axial force and the shear force mobilised in the bolt in both the elastic and plastic stages. Moreover, the large plastic displacements of the bolt occurring during the loading process are taken into account. The comparison of numerical versus experimental data gives reliable results.