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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Analysis of the mechanical test results (static tension and hardness) on specimens in naturally-aged and normalized conditions showed that they do not fully demonstrate a state of material degradation. It is assumed that the basic factor for assessing material features are changes in its internal structure resulting from the structural processes of degradation. These structural changes find their reflection in changes in the material toughness.

2.2. Material toughness

The results of toughness tests are not directly used in static calculations such as ultimate strength or yield strength. Toughness experiments are usually used to calculate material transition temperature from plastic to brittle mode T t (DBTT ductile-to-brittle transition temperature). A notch toughness experiment is the simplest test method for calculating fracture resistance. Practically, the criteria for transitional fracture behaviour are:  the level of absorbed energy necessary to break a specimen, i.e. 27 J for specimens with a V-notch,  changes in the fracture appearance FA defined as the transition from fibrous (plastic) to brittle (50 % of cleavage fracture). When giving the transition temperature, the criterion used to determine it should be provided (T 27J , T 50% ). Temperature T 27J at which minimum impact energy KV (on Charpy V specimens) should not be less than 27 J, is also given by Eurocode EN 1993-1-10. Similarly, product standards (EN 10025-2) generally require that the impact energy at a given temperature (depending on subgrade) should not be lower than 27 J. These code requirements are recommended when selecting steel for new structures; they do not refer to structures in operation. Toughness values are treated by technologi sts as one of the most important indicators of steel’s mechanical properties. Transition temperature is of practical importance since it is a measure of the material’s usability under impact loading and indicates the temperature at which sudden brittle fracture may arise. It is of particular relevance to old bridge structures because:  the ageing of the material exacerbates the development of brittle fracture, clearly increases the transition temperature and the material becomes harder, in addition to losing its ability for greater plastic deformation,  the transition temperature clearly increases under fatigue, pulsar actions and dynamic actions,  operation is at lower temperatures for a period of time,  a large number of stress concentrators in the form of non-metallic inclusions is present in mild steels, in addition to changes due to micro-structural degradation processes. A thorough assessment of material issues enables a more precise calculation of durability in bridge structures with a long service life. This paper thus aims to do the above, by analyzing the impact toughness of mild steels on five railway bridge structures constructed from 1875 to 1930.

Table 1. Technical and structural data for the five railway steel bridges.

Data of Charpy KV

Number of tracks (spans)

Bridge No.

Year of construction

Localization (line and km)

Span data 1) L, H ( m )

Structure

Location of specimen Vertical web t = 12 mm

Type of specimen 3)

Wrocław – Gubinek km 114.278 Grzmiąca – Kostrzyń km 224.915 Zbąszynek – Gorzów Wlkp. km 30.440 Warszawa – Kunowice km 26.806 Poznań – Skandawa km 88.405

34.50 4.80 25.00 3.27 (2.12) 24.60 2.22 12.10 0.60 2) 18.90 1.80 (1.45)

S N S N S N A S N

Truss deck

1 (3)

1

1875

Bottom bracing L200×100×14 Stringer web I360 I380 Flange I600 B (Grey)

2

1882

Truss deck

1 (1)

Semi-through plate girder

3

1887

3 (2)

Filler beam deck I600 & I600 B

2 (1)

4

1890

Plate girder deck

Top flange 320×10

SS N

5

1930

2 (3)

1) Value in brackets is the height at support 2) Bridge 4 – H is the height of rolled beams 3) Specimens: S – naturally-aged, N – normalized, A – fully annealed