| The flexible protection system has excellent resistance to rockfall impact of up to tens of thousands of joules,because of its excellent inelastic large deflection ability due to the good cooperation of system components.However,the inelastic large deflection of the flexible protection system after impact can easily lead to the accumulation of rockfalls.Besides,the accumulation of rockfalls makes it difficult to maintain the system,and seriously affects the resilience of the system.Furthermore,the difficulty of the resilience improvement is increased.Therefore,this thesis studied the resilience improvement method of the flexible protection system on the traffic artery near the cliff and valley,and studied the correlation between the structural damping and resilience of the flexible protection system,the mechanism and control method of rockfall trajectory and the calculation method of impact force.The calculation method considered the influence of the flexibility of the ring net.Then this thesis established the resilience improvement design method of the steel canopy protection system and proposed a steel canopy protection system with strong resilience.What’s more,two full-scale impact tests and the numerical simulation were carried out.Based on the study above,the effectiveness of the resilence improvement design method and the resilient protection effect of the system was velidated.The specific research content of this thesis was detailed as follows:(1)The technical development and current status of the flexible protection system were summarized,and the existing problems were analyzed(Chapter 1).The current research on the resilience of the flexible protection system was summarized by three parts: the existing resilience evaluation methods,impact force calculation methods and the impact mechanical behavior of the systems.The shortcomings of the existing research were pointed out.Based on this,the research content and technical route of this thesis were determined.(2)The controlling of resilience and the design method of the protection system were proposed(Chapter 2).The correlation between damping and resilience was analyzed.It was pointed out that the resilience decreased as the damping increases.Flexible protection systems were divided into three categories: high-elastic system,medium damping elastic system and high-damping system.Besides,the deflection calculation method of the protection systems was constructed,and the ultimate deflection of the system was studied.The correlation between the ultimate deflection and the rockfall trajectory has made clear.Then the calculation method of the critical pavement angle of the systems was established.The impact force calculation method based on the Hertz collision theory was established.And the impact force calculation method considered the influence of the flexibility of the ring net.(3)The structural system of the resilient steel canopy system and the connection of each component were studied.The full-scale impact test and numerical simulation were carried out(Chapter 3).A prototype model of the steel canopy protection system with a nominal energy level of 500 k J was designed.Two tests were carried out with impact energy of 150 k J and 500 k J respectively.Besides,the explicit dynamic analysis was carried out.The impact mechanical behavior of the system was studied.The test results showed that the response roughly experiences three stages: large deflection with high tension,spring back,and system recovery.The net formed a Y-shaped tension band under the impact,and the plastic deformation of the mesh occurred in the tension band area.The residual deflection led to the funnel-shaped deformation in the impact contact area.The residual deflection of the net was9.6% and 17.8% of the initial deflection,respectively.(4)According to the parametric analysis,the effectiveness of the resilience improvement method was velidated,and the resilient protection effect of the system was clarified(Chapter 4).The energy dissipation characteristics of the canopy were studied.It was shown that damping was the main energy dissipation means of the system.The damping dissipated more than 60% of the total kinetic energy of the system.The energy dissipation of ring net was about 19% of the total kinetic energy.The residual working capacity of the system is relatively significant.Besides,the hammer can be thrown out of the system,and the rebound height of the hammer was increased with the increase of the impact energy.It was shown that the system can control the trajectory of rockfall.The residual deflection of the steel canopy protection system and the flexible rockfall barrier system were compared.And it was found that the residual deflection of the canopy was only 22% of that of the flexible rockfall barrier system.The impact force of the canopy and the gravel cushion were compared.And it was found that the impact force of the canopy was only about 33% of that of the gravel cushion.In general,the resilience of the system showed comprehensive comparative advantages.This thesis has successfully realized a breakthrough in the buffering mechanism of the flexible protection system by transferring a large deflection and energy dissipation mechanism to a large deflection and energy storage mechanism.The resilience of the flexible protection system has effectively improved.The rockfall movement calculation method of the resilience improvement design method can be used for the pavement design of the steel canopy protection system.And the error of the method was less than 7% compared with the experimental results.The impact force calculation method can be used for the design of system component selection,and the error of the impact force calculation method was less than 15% compared with the experimental and numerical simulation results.In addition,the structural system of the resilient steel canopy system proposed in this thesis took into account the optimizing control of impact force and residual deflection,and the system showed good resilience improvement. |
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