Bolts, as a rule, carry only shear, but sometimes they carry both shear and tension. 1-2e Torsion is the stress which tends to distort by twisting. You produce a torsional force when you tighten a nut on a bolt. The aircraft engine exerts a torsional force on the crankshaft or turbine axis. Sometimes a member has alternate stresses, such as compression one instant and tension the next.
Some members can carry only one type of stress.
Since any member is stronger in compression or tension than in bending, members carry end loads better than side loads. In order for a truss to be rigid, it must be composed entirely of triangles. When the load on a truss acts in one direction, every alternate member carries tension while the other members carry compression. When the load is reversed, the members which were carrying compression now are subjected to tension and those which were carrying tension are under compression. These features make it rigid, strong, and light.