Abstract: Due to thstrain-softening of materials or due to the cross-sectional distortion of thin-walled beams in their large deflection,the moment-curvature relation of beams may display a hardening-softening characteristic.The recent work carried out by a research groupin Peking University has confirmed that when a semi-infinite beam with softening property is subjected to a suddenly applid constant velocity at its tip,softening may develop into asegment of finite length and travel along the beam. Meanwhile,in ord...