Experiments and Dynamic Finite Element Analysis of a Wire-Rope Rockfall Protective Fence

Abstract

The imperative need to protect structures in mountainous areas against rockfall has led to the development of various protection methods. This study introduces a new type of rockfall protection fence made of posts, wire ropes, wire netting and energy absorbers. The performance of this rock fence was verified in both experiments and dynamic finite element analysis. In collision tests, a reinforcedconcrete block rolled down a natural slope and struck the rock fence at the end of the slope. A specialized system of measuring instruments was employed to accurately measure the acceleration of the block without cable connection. In particular, the performance of two energy absorbers, which contribute also to preventing wire ropes from breaking, was investigated to determine the best energy absorber. In numerical simulation, a commercial finite element code having explicit dynamic capabilities was employed to create models of the two full-scale tests. To facilitate simulation, certain simplifying assumptions for mechanical data of each individual component of the rock fence and geometrical data of the model were adopted. Good agreement between numerical simulation and experimental data validated the numerical simulation. Furthermore, the results of numerical simulation helped highlight limitations of the testing method. The results of numerical simulation thus provide a deeper understanding of the structural behavior of individual components of the rock fence during rockfall impact. More importantly, numerical simulations can be used not only as supplements to or substitutes for full-scale tests but also in parametric study and design.

Prototype of a wire-rope rockfall protective fence developed with three-dimensional numerical modeling

“…These results show that the developed prototype fence can be strengthened considerably by optimizing the AFF simply by altering the torque of the M20 bolts [12]. The fence becomes more effective as it is made stiffer, which is unusual for flexible fences.…”

“…Although only two features (the post spacing and number of wire netting layers) were altered from our previous WRF [12] to create the developed prototype, we anticipate that these variations will invoke large changes in the structural response of the fence. Expensive experimental approaches have routinely been used to study such prototypes.…”

“…Expensive experimental approaches have routinely been used to study such prototypes. Here, we employ our previously developed numerical approach [12], which has already been assessed and validated using experimental data obtained in full-scale tests. This inexpensive, accurate approach can precisely produce the nonlinear response of a fence subjected to impacts under dynamic conditions, helping to clarify the capacity of a fence under various impact conditions.…”

“…Figure 4 shows the bending moment versus deflection curve of posts obtained from a static laboratory pre-test (refer to Ref. [12] for more details), and an assumed stress-strain curve of the posts. A simplified model of the energy absorbers with AFF=45.4 kN is shown in Figs.…”

“…It is likely that at an energy of 800 kJ, AFF=60 kN is a threshold at which the absorbers still affect fence elongation. Moreover, according to a preliminary test of the energy absorbers, the maximum friction force acting between the wire rope and absorber is probably three times the AFF [12]. Therefore, AFF=70 kN is inappropriate because the critical strength of the wire ropes is 180 kN.…”