Lines of Influence: Theorem of Virtual Displacements

This lecture covers the concept of lines of influence, focusing on finding the most unfavorable position of a load train without calculations. It explains how to draw the line of influence for support reactions and internal forces on a beam, as well as determining the sign in a line of influence. The calculation of lines of influence is demonstrated through the equilibrium of fragments and the theorem of displacements. The virtual deformation associated with the desired static effect is explored to draw lines of influence without calculations, emphasizing the importance of checking the sign of the desired static effect. Examples are provided to illustrate the process of finding the shape of influence lines for support reactions and embedding moments.