Issue 43

A. Luciani et alii, Frattura ed Integrità Strutturale, 43 (2018) 241-250; DOI: 10.3221/IGF-ESIS.43.19 246 Therefore, the six models set up for the research are: - models from (a) to (d) simulate the failure of connections made by rope clips of the upstream cables, due to installation problems or to clip corrosion. In the numerical models, this kind of damages has been simulated simply removing one of the upstream cables from the computation i.e. the connection is not working and thus the cable cannot withstand any stress. Moreover, models (c) and (d) simulate also the failure of one anchorage of the upstream cables due to a not correct grouting. In the numerical model this possibility is simulated removing from the simulation the cables that are restrained by that anchorage. - model (e) and (f) reproduce the effect of different installation geometry due to local conditions. The goal of these models is to study the influence of anomalous geometrical installations with reference to the one tested following the ETAG027 geometry. Model (e) represents a case with short and horizontal upstream cables. The original model has oblique upstream cables of 7.7 m while in this model they are horizontal with a length of 5.7 m while model (f) reproduces the effect of very long upstream cables. The upstream cables of this model are 20.0 m long. In the numerical model, only the geometry and length of upstream cables have been changed from the original model. (Fig. 5). On these six modified models impact tests were performed at different energy levels aiming to identify the maximum energy the modified net fence can withstand without failure of one of the principal elements. Failure of cables and energy dissipating devices was established when one of these elements reached a plastic strain bigger than that correlated to the ultimate stress. Since the model uses an equivalent net, the ultimate stress of the net was unknown, for it may be different from that of the real ring net. Therefore, the equivalent net was considered failed if at least one of the elements composing the net reached a plastic strain bigger than the maximum recorded during the MEL simulation. Once the maximum energy the modified model can withstand has been defined, the residual efficiency ( ef r ) of the net fence can be evaluated as (%) MW ef nom E r E  where MW E is the maximum energy the net fence can withstand and nom E the nominal energy of the net fence according to the ETAG 027 classification. The values of residual efficiency of the models are reported in Tab. 2. Table 2: Summary of the results of the numerical simulations. Model Problem simulated Maximum energy withstood (kJ) Residual efficiency (%) a Failure of one clip connection or of one upstream cable 3000 100 b Failure of one clip connection or of one upstream cable 3000 100 c Failure of two clip connection or of two upstream cable or of an anchorage 2900 97 d Failure of two clip connection or of two upstream cable or of an anchorage 3000 100 e Short and horizontal upstream cables 2400 80 f Long upstream cables 2600 87