If you select the Internal Engine method for calculating internal forces, the model supports the linear superposition of any combination of point loads, uniform line loads or linearly-non-uniform line loads (such loads are determined by the model using the tributary areas of members and assuming one-way slab action to distribute loads placed on the slab to supporting elements). Line loads can occupy the entire span or any portion. Parabolic, circular, or other non-linear non-uniform line loads are not supported, but can be approximated by a series of trapezoidal loads. Moment, shear, and deflection profiles are calculated based on closed-form solutions, all available in Young (2001).
Irrespective of the method for calculating internal forces, to maintain a current and correct profile of the moment, shear, and deflections, loads are superimposed by addition (and subtraction, if necessary) to create a total polynomial profile. This allows the application to keep a complete and exact profile of the properties. Since the superposition uses closed-form analytical solutions, there is no numeric approximation.