Nonlinear stability calculation

Non-linear stability is in its first phase calculated as normal nonlinear calculation using N-R method. The load is incremented in steps, but the incrementation does not stop at the load intensity defined by the non-linear combination and continues until the singularity is reached. Then the solution goes back to the last regular state and the critical load intensity is found from this state by means of eigenvalues, i.e. refined solution is sought in the interval between the last regular and singular state.The accuracy of the solution is therefore determined by the number of load increments. The load intensity defined in the non-linear combination has two meanings. First, when divided by the number of the increments, it specifies the size of load increment and, second, the calculated coefficient of the critical load is related just to it.