Issue 43

E. Maiorana et alii, Frattura ed Integrità Strutturale, 43 (2018) 205-217; DOI: 10.3221/IGF-ESIS.43.16 210 where the slip load is the load corresponding to a deformation of 0.02 in., that is 0.5 mm. Tab. 5 shows the list of specimen series, surface treatment and the reference standard. As many products report results for the slip coefficient found following the procedure of the Italian former standard CNR UNI 10011 [20], for a comparation also these results are reported. According to CNR UNI 10011 [20], the preload was found by F C,P = 0.8 f k,N Ares where f k,N = min{0.7 f u,b ; f y,b } ; for example, for bolts M20 class 10.9 f k,N = 700 N/mm 2 and A res = 245 mm 2 so F P,C = 137 kN (25% less European code) and the corresponding tightening torque M r = k F P,C d that is 550 Nm. Note that CNR UNI 10011 [20] gave a fixed value k = 0.2 and the partial safety factor  M in formula of resistance force was the same as in EN 1993-1-8 [1] at ultimate state limit. Series Product n. Coating Bolts (diam. and grade) Standard Slip force F Si [kN] Slip coeff.  m Slip coeff.  k 1 2 3 - - 1 1 M20 10.9 M20 10.9 M20 10.9 EN 1090-2 EN 1090-2 CNR UNI 10011 353 340 227 0.52 0.50 0.42 0.45 0.45 0.38 4 2 2 Ø20 ASTM A490 RCSC 278 0.64 0.47 5 3 2 Ø20 ASTM A490 RCSC 223 0.51 0.28 6 4 3 M20 10.9 EN 1090-2 263 0.39 0.34 7 5 3 M16 10.9 CNR UNI 10011 220 0.62 0.58 8 5 3 M16 10.9 EN 1090-2 311 0.45 0.41 9 6 4 Ø20 ASTM A490 RCSC 152 0.34 0.29 10 7 1 Ø20 ASTM A490 RCSC 243 0.56 0.45 11 7 1 M20 10.9 EN 1090-2 354 0.51 0.43 12 8 3 M20 10.9 EN 1090-2 230 0.34 0.29 Chemical composition: 1 inorganic zinc ethyl silicate bicomponent; 2 inorganic zinc-rich bicomponent; 3 inorganic zinc polyethylene silicate bicomponent; 4 inorganic zinc silicate bicomponent Table 5: Series of tests with different coating products (final value of  in bold font). Series n.1. Slip test on only blasted surfaces The material of the specimens was weathering steel with characteristics as in EN 10025-5 [21] S355J0W. Fig. 2 shows the geometry of the specimens. Figure 2 : Geometry of the specimen. Surfaces were cleaned at grade Sa2½, i.e. surfaces sandblasted as white metal surface; mean profile roughness was about 100  m. The bolts used to assembly the specimens were HV M20 grade 10.9. To reach the preload force the bolts, as in the Combined method, were subjected to a tightening torque of 334 Nm, that is 75%M r , plus a rotation angle A = 90°, corresponding to a final tightening torque of about 520 Nm. The instrument utilized for measuring the relative displacements of the plates in the connection is formed by four transducers of inductive displacement (LVDT) useful to find displacements δ in the order of 10 -3 mm. The tensile force applied was measured with a load cell installed in a universal test machine MetroCom of 500 kN as in Fig. 3. The specimen number five (S5), as reported in Annex G of EN 1090-2 [2], was loaded with a force equal to 90% of the mean value of the sliding forces F Si found for the other previous four specimens, for a period of three hours. Over this time the displacement recorded was under the limit of the standard, 0.002 mm, so five tests were sufficient for the statistic evaluation of the slip factor (Fig. 4) and from each specimen, two values S i were found.