Issue 43

E. Maiorana et alii, Frattura ed Integrità Strutturale, 43 (2018) 205-217; DOI: 10.3221/IGF-ESIS.43.16 212 Series n.2. Slip tests on specimens blasted and rusted in a saline atmosphere A set of blasted specimens, steel grade EN 10025-2 [21] S355J2+N, was exposed for one week above a box with saline water (H2O con 3% of NaCl). Fig. 6 shows the final surface aspect of the specimens. The surfaces in contact were brushed and the connection was closed. The tightening torque applied was 545 Nm. Figure 6 : Blasted and rusted specimens. The specimen number five (S5), as reported in the code, was loaded with a force equal to 90% of the mean value of the sliding forces found for the other four specimens, for a period of three hours. Over this time the displacement recorded was under the limit of the norm, 0.002 mm, therefore five tests are sufficient for the statistic evaluation of the slip factor. The values obtained by the tests were processed, obtaining the mean value of the slip factor  m = 0.500, a standard deviation s  = 0.023, thus a characteristic value  k = 0.453 is achieved. Fig. 7 shows the test results. Figure 7 : Blasted and rusted specimens. Dashed line: mean value  m ; continuous line:  k . Slip tests on blasted and coated surfaces Fig. 8 shows the specimens of series n.6 under test. For specimen number five (V5), the displacement recorded was 0.0280 mm for the upper limit and 0.0335 mm for the lower limit, thus above the limit of the standard, so five tests are not sufficient for the statistical evaluation of the slip factor and an extended creep test procedure should be necessary. Otherwise, apart from the delayed slip of the fifth test, the values obtained by the tests were processed obtaining the mean value of the slip factor  m = 0.387, a standard deviation s  = 0.022, thus a characteristic value  k = 0.343 is achieved. Fig. 9 shows the test results. Since the characteristic value for the slip factor using specimens painted with product n.4 was very low compared to the previous results, the authors thought that the problem was both the thickness of the paint (for thicknesses greater than 100  m the cracking of the film may occur), and the product itself, therefore inorganic zinc-rich primer with a 5% higher weight was used, i.e. product n.5. Fig. 10 shows the specimens of series n.8 under test. It is product n.5 tested following EN 1090-2 [2]. Using the data of the first four slip test specimens, the mean value  m = 0.45 and a characteristic value  k = 0.41 were achieved, but the creep test, on the fifth specimen, failed with relative displacements of 0.0245 mm and 0.012 mm that were observed after half an hour, instead of the maximum 0.002 mm over three hours.