被动柔性防护系统对落石冲击作用的传播效应

被动柔性防护系统遭受落石冲击作用时的波传效应对系统耗能效率存在重要影响，对此开展了能量为1 500 kJ的3跨足尺模型冲击试验，结合LS-DYNA开展了非线性动力分析，对比研究了柔性防护系统的冲击变形、特征点位移和钢丝绳拉力等结构响应沿支撑绳纵向的传播特征. 进一步开展了4跨、5跨、6跨和7跨模型的冲击动力学模拟试验，研究了纵向传播距离增加对冲击响应的影响，包括支撑绳拉力、网片内力和系统冲击力随随波传距离增加的衰减率、构件耗能率和冲击历程的多阶段耗能率变化. 研究结果表明:冲击跨支撑绳拉力明显高于边跨；冲击跨网片内力最大，两侧网片内力急剧衰减，呈高斯型衰减分布；随着系统跨数增加，落石冲击变形极值变化较小，但变形时程变化差异较大；内力衰减变化明显，7跨模型中，支撑绳内力衰减超过了50%，网片内力衰减了40%，冲击力衰减了14%；随着系统传播距离的增加，网片、减压环以及钢柱的耗能减少，钢丝绳和其他摩擦耗能增加，第1、2阶段耗能增大，第3阶段耗能减小. 

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.