Frame analysis for non-linear behavior can be made either by simulating a load control or deformation control test setup. In the latter approach, a set of deformations is increased to the structure and the corresponding set of loads is calculated. In an analysis for load control, a load pattern is incremented to the structure up to a peak value. It should be noted that analysis beyond the peak load can only be made by employing additional special techniques. Usually, iterative procedures are required to achieve convergence for the load-deformation relationships and one of the following three techniques can be used:
- Tangent stiffness method (also referred to as the Newton-Raphson method).
- Initial stiffness method (also referred to as the modified Newton-Raphson method).
- Secant stiffness method.