unit test for this objectives must be implemented:
LoadInternalForce_uniformload_eulerbernoullybeam_dirY LoadInternalForce_uniformload_eulerbernoullybeam_dirY LoadInternalForce_uniformload_truss
LoadInternalForce_concentratedLLoad_eulerbernoullybeam_dirY_fz LoadInternalForce_concentratedLLoad_eulerbernoullybeam_dirY_my
LoadInternalForce_concentratedLLoad_eulerbernoullybeam_dirZ_mz LoadInternalForce_concentratedLLoad_eulerbernoullybeam_dirZ_fy
LoadInternalForce_concentratedLLoad_truss_fx LoadInternalForce_concentratedLLoad_shaft_mx