PSI - Issue 5

Hołowaty J. et al. / Procedia Structural Integrity 5 (2017) 1043 – 1050 Hołowaty / Structural Integrity Procedia 00 ( 2017) 000 – 000

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Only the steel from bridge No. 1 with carbon content C = 0.258 % had impact energy KV = 28.6 J at temperature 0 °C which slightly exceeded the limit value of 27 J. For steel from bridge No. 3 the low values were measured over the range of temperatures. Low values of impact energy are an important issue if any part of a structure is subjected to impact loading. Normalization of the steels considerably improves their impact strength. The average increase in impact strength for bridges Nos. 2 ÷ 4 was 4.7 times and for bridges Nos. 1 and 5 was 1.8 times. Toughness at the time of delivery, at bridge construction, was insufficient only in bridge No. 5 (Fig. 3) and in the case of subgrade J0 did not fulfill the requirements of EN 10025-2:2004. For the rest of the bridges impact energy at temperature 0 °C was from 37.7 to 63.4 J and was higher than the contemporary requirements KV = 27 J. In contrast to normalization, full annealing only slightly increased the impact strength of the steel (Table 4). In the case of bridge No. 3 for subgrade J0, the increase in toughness was 78.3 and 82.3 %, while for subgrade J2 (-20 °C) the increase was only 16.3 and 20.8 %. The steel design strengths for the bridges were assessed according to the Polish Standard for steel bridge structures (PN-S-10052:1982), taking into account the partial coefficient for material γs = 1. 20. For bridges Nos. 1 and 2 the design strength came to f d = 280 MPa, while for the remaining bridges it ranged from 185 to 210 MPa. The specified “ageing index”, determined as equal to the ratio of material impact toughness after ageing to non -ageing (normalized specimens) at temperature -20 °C, ranged from 0.30 to 0.46 for bridges Nos. 1 ÷ 4 and was 0.86 for bridge No. 5. At temperature 0 °C the ratios were from 0.14 to 0.20 (bridges Nos. 2 ÷ 4), 0.60 and 0.50 (bridges Nos. 1 and 5). These values are evidence of a great influence of so-called ageing effects. For the steels in post-service conditions (S) from bridges 1, 2, 4 and 5, the ductile-to brittle transition temperature ranged from -1 to +20 °C and for the steel from bridge No. 3 it was impossible to determine (Fig. 3). This should be considered as an highly dangerous phenomenon from a service point of view since there is a possibility of brittle fracture development in winter conditions. The findings given in the paper relate to old mild steels and should not be applied to contemporary steels in new structures. For new bridge structures, the steel should be selected in accordance with EN 10025:2004, where the requirements for notch toughness as a design service temperature function and plate thickness are given. Assessments of old riveted bridges to avoid brittle fracture to EN 1993-1-10:2005 may be carried out under the guidance given in Sedlacek el al. (2008). 6. Summary The structural steels in old railway bridges exhibit a wide range of mechanical properties and their notch toughness is usually very low [Markworth (1967)]. The results in this paper confirm this. Hołowaty, J., 201 3 . Removing w eak spots from Polish r ailways. Structural Engineering International, SEI Volume 23, Number 1, February 2013. International Association for Bridge and Structural Engineering (IABSE), 85-88 Hołowaty, J., Wichtowski, B., 201 3 . Properties of structural steel in early railway bridges. Structural Engineering International, SEI Volume 23, Number 4, November 2013. International Association for Bridge and Structural Engineering (IABSE), 512 - 518. Hołowaty, J., 201 6 . Analysis of material properties and weldability of s teel in old r ailway bridges , IABSE Congress – Challenges in Design and Construction of an Innovative and Sustainable Built Environment. Stockholm, 21 - 23 September 2016, 2494 - 2501. Kühn , B., Lukić , M ., Nussbaumer , A. , Günter, H.P., Helmerich , R., Herion , S., Kolstein , M.H., Walbridge , S., Androic, B., Dijkstra, O, Bucak, Ö. , 2008. Assessment of existing steel structures: Recommendations for estimation of remaining fatigue life. ECCS & JRC, European Communities: Luxembourg, pp. 92. Markworth, E. , 1967. Alte Brückenbaustäle. Deutsche Reichsbahn: Magdeburg, pp. 83 . Sedlacek, G., Feldman, M., Kühn, B., Tschickardt, D., Höhler, S., Müller, C., Hensen, W., Stranghöner, N., Dahl, W., Langenbe rg, P , Münstermann , S ., Brozetti, J., Raoul, J., Pope, R., Bijlaard, F., 2008. Commentary and work examples to EN 1993 - 1 - 10 “Material toughness and through thickness properties ” and other toughness oriented rules in EN 1993. ECCS & JRC, European Communities: Luxembourg, pp. 250. References