Compression, Tension, Bending and Torsion: How Forces Change Structures

Why can a bridge remain perfectly still while its members are working hard? A compressed column, stretched cable, bending shelf and twisting drive shaft all carry loads through different internal actions. This section explains how external loads pass through structures, how supports provide reactions and why equilibrium does not mean that forces have disappeared. A stationary structure can contain internal forces, elastic deformation and stored elastic strain energy.