Propagation Effect of Passive Flexible Protection System on Rockfall Impact

The propagation effect of passive flexible protective system under rockfall impact has an important influence on the energy consumption efficiency of the system, a full-scaled impact test, in which the test model had 3 spans in length, was conducted under a kinetic energy of 1 500 kJ. Based on LS-DYNA, the nonlinear numerical simulation on the whole process of the collision and interception was carried out. The comparative analysis on the system deformation, the displacement of characteristic points and tension in the cables between experimental and numerical results was studied. In particular, the propagation effect of the impact load along the longitudinal direction was investigated. Then the numerical models with 4, 5, 6, and 7 spans were calculated respectively to explore the influence of the number of spans on the ultimate system deformation. The attenuation percentage was introduced to discuss the reduction in the internal forces of the cables and wire-ring net, as well as the impact force according to the increase of span number. An energy dissipation ratio was defined, and the ratios distribute among each component and within the three stages as the span number change were analyzed. The results show that the internal force of the support cable is higher than that of the lateral span significantly. The peak internal force of the wire-ring net appears in the impact area, and the internal forces of the net on both lateral sides are very small, so that it presents a Gauss attenuation distribution. With increase of the span number, the maximum elongation of the system changes little, but the time history values have evident differences. The internal force and the impact force decrease obviously, in the 7-span model, the lower support cable tension, the peak internal force of the wire-ring net, and the impact force reduced by 50%, 40%, and 14%, respectively. With the increase of propagation distance of the impact load due to the bigger length of system, the energy dissipation of the wire ring net, the brake rings and the steel column is reduced, and the energy consumption of cables and other components is increased, the energy dissipation ratio increases within the first and second mechanical stages, and decreases within the third stage.