The objective of this work is to develop a tool for obtaining envelopes of internal forces due to load-trains in the FTOOL software. Usually, envelopes are obtained through interpolation of limiting values on pre- selected sections along the structure. These values are obtained based on the positioning of the loadtrain in relation to influence lines of internal forces. The determination of limiting values of an effect at a section represents an optimization problem whose objective is to minimize or maximize the values of that effect in relation to the position of a load-train that passes along the structure. However, there is no analytical expression that defines a limiting value of an effect on a section for a specific load-train. Therefore, classical optimization methods cannot be used to solve this problem. Rather, the solution requires a method that does not require derivatives of the objective function. For this reason, this work adopts algorithms of the Evolution Strategy (ES) to achieve the limiting values due to load-trains. Two distinct algorithms of the ES, known as ES − + ) 1 ( (lambda) and ES − + ) ( (lambda) (mi) , were implemented. In addition to the ES algorithms to trace the envelopes, another process of solution called Force Brute was developed. It consists of moving the load-train in pre-determined steps along the structure and calculating minimum e maximum values. In general, the ES method converges to the correct solution. However, there are cases, depending on the complexity of the load-train, that the algorithms do not find the exact limiting value (although usually very close to it). It was observed that the ES results could be complemented and improved with results from an inexpensive solution in which concentrated loads are positioned on peak values of the influence lines.