Experimental, numerical and analytical modelling of a newly developed rockfall protective cable-net structure

Abstract

Abstract. An innovative configuration of pocket-type rockfall protective cable-net structure, known as Long-span Pocket-type Rock-net (LPR), has been developed in Japan. The global performance of the proposed system was initially checked by the experimental (full-scale) modelling. Given the various limitations of the physical experiments, particularly for the parametric study to have a detailed understanding of the newly developed system, a reliable and simplified method of numerical modelling is felt necessary. Again, given the sophistication involved with the method of numerical simulation, a yet simplified modelling approach may prove more effective. On top of this background, this paper presents a three-tier modelling of a design of LPR. After physical modelling, which has revealed that the displacement response may be taken more vital for LPR performance, Finite Element based numerical modelling is presented. The programme LS-DYNA is used and the models are calibrated and verified with the element-and structure-level experiments. Finally, a simple analytical modelling consisting of the equivalently linear and elastic, lumped-mass, singledegree-of-freedom system, capable of predicting the global displacement response, is proposed based on the basic principles of conservation of linear momentum and energy. The model is back-calculated and modified from the analyses of the verified numerical model.

Numerical and analytical investigation towards performance enhancement of a newly developed rockfall protective cable-net structure

“…The system performed well; no damage was recorded and it was confirmed that the instrumented forces developed in the cables were well below the safety margin defined by the (yet conservative) Allowable Stress Design philosophy (see Dhakal et al, 2011a for further details). Moreover, given the very important condition that the targeted sites of LPR application typically have very limited space between the hillslope and the road-carriageway the former verification implied that the global out-of-plane displacement response of the wire-net (which may be simply referred to as "displacement" hereinafter) might be more vital in evaluating the performance of the structure.…”

“…Lam et al, 2010;Yang et al, 2011;Dhakal et al, 2011a;Ali et al, 2011). As such, the wire-net is the major structural component of the rockfall restraining LPR system and contributes more than 70 % to the total mass.…”

“…The real wire-net has material-less holes in their grids. However, in the verified numerical modelling of the R-LPR, exercised in the code of LS-DYNA as described in the companion work, we conveniently modelled the 50 mm × 50 mm × 4 mm mesh with the equivalent continuum shell elements by utilizing the BelytschkoTsay Shell formulation and Fabric material model available in the code (see Dhakal et al, 2011a for more information). The equivalent shell elements were assumed to have the density equal to that of ordinary steel (7840 kg m −3 ) and hence the equivalent thickness equalled to 0.587 mm (4.6 divided by 7840).…”

“…In the companion paper Dhakal et al (2011a), we introduced a particular type of rockfall protective cable-net structure (barrier), called Long-span Pocket-type Rock-net (abbreviated by LPR), developed newly in Japan, and discussed its modelling in three tiers. The expensive full-scale experimental modelling (full-scale test: FST) was followed by the cheaper and a bit simpler numerical and analytical modelling.…”

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

“…This explicit program is used to capture dynamic and extremely rapid responses of structures to severe impact loads [9]. The numerical model is primarily based on simplifications of the material properties of fence components, such as the wire ropes (Fig.…”