Issue 43

A. Luciani et alii, Frattura ed Integrità Strutturale, 43 (2018) 241-250; DOI: 10.3221/IGF-ESIS.43.19 244 Fig. 3 compares model deformation during MEL test at six different times: particularly t = 0 s is the first contact of the block with the net, t = 0.36 s is the breaking time and t = 6.00 s is the test end time. Fig. 4 shows the plastic strain in the central panel of the net during the simulation; it is possible to see that the highest deformations occur in the contact area of the block with the net, then the deformation extend to the panel with a cross shape and this result is very close to what was observed in real tests [10,11]. Figure 3: Numerical modelled net fence during the MEL test. N UMERICAL SIMULATION OF DAMAGES n order to evaluate the influence of the problems detected during the site survey [29], the numerical model was modified to reproduce damaged conditions. These conditions represent the most common local damages and the ones that were most frequently highlighted by the site survey [29]. The model has not the ability to take into account a reduction of the overall properties of the net barrier since them can be difficulty described and the research has been focused on those damages that can be modelled as the removal of a structural rope or an incorrect assembly of one or more elements of the barrier itself. Specifically, these conditions are: - damages to the upstream ropes or to the clamp connections; these situations can be due to installation of the clumps not in accordance with the regulations in force [31] in terms of number, distance and torque applied to the fastener or to damages of the connections and of the ropes caused by impacting blocks; - damages to the anchorages, such as failure or under efficiency of the anchorages due to wrong installation or damaging during the device life; - installation geometries different from those prescribed by the producer; this is a common issue for to the geometry peculiarity of many sites; in the site survey several cases have been observed ranging from barriers with short and sub-horizontal upstream ropes to barriers with extremely long upstream ropes. Time-dependent damages to the barriers can be related to corrosion on ropes and clip connections. Nevertheless, in the barriers analyzed during the site survey, corrosion affects only some of the secondary metallic elements, but not ropes. This is due to the non-aggressive environment of installation (usually C1-C2 following UNI EN ISO 9223 [32]) and to the protection nowadays used against corrosion (zinc and zinc-aluminum coatings) that ensure the durability for the life span of the protection devices. I