Inelastic Response of Beams to Moving Loads

The dynamic response of elasto-inelastic beams to moving loads is studied analytically based on a discrete beam model consisting of massless rigid panels connected by flexible joints with point masses. In determining the response, both the elastic and inelastic properties (including strain hardening) are taken into account. The moving load may be an unsprung mass or a sprung mass, or both, moving at a uniform speed. A feature in the analysis is the consideration of the discontinuities in vertical velocities and accelerations as an unsprung mass crosses a joint of the model beam. The emphas of the numerical results, obtained for simply supported bilinear beams, is on unsprung loads. Results indicate that for an elastic perfectly-plastic beam, loads smaller than the static yield load can cause permanent deformations. However, loads considerably heavier than the static yield load can still cross the beam. In addition to the load mass, the major factors influencing the inelastic deformations of the beam are the load speed and the inelastic stiffness of the beam. Even a small amount of positive inelastic stiffness reduces the permanent beam displacements significantly.