**3. Quality of welds in railway bridges according to Non-Destructive Testing (NDT)**

The aging of metallic materials favors the formation of brittle cracks as the ductilebrittle transition temperature clearly approaches higher values. Strains associated with aging depend on the location in the structure. They are particularly dangerous in stress concentration areas, e.g. around welding imperfections (WIs) and in heat-affected zones (HAZs). According to Neuber [3, 12], the largest concentration of stresses is

associated with ellipsoidal and longitudinal welding imperfections with an elliptical cross section (**Figure 3**).These types of imperfections include cracks and lack of fusion, as well as band slag intrusion and incomplete side fusion. This issue is becoming particularly significant for bridges constructed after 1936, considering the poor quality of connecting welds. This has been confirmed by radiographic tests performed on bridges in service on Polish railway lines [3].

The Steel Structure Chair at the Technical University in Szczecin (now WPUT) carried out radiological tests on butt splices in the steel girders of around 200 railway bridges on the Polish railway network. For 154 bridges, including 124 plate girder bridges and 30 truss bridges, the exact time of construction was also established.

The range and results of in situ nondestructive radiological tests on the railway bridges are given in two histograms (**Figures 5** and **6**). The tests consist of the sum of 5 year intervals which take into account the bridge construction period from 1936 to 1975. **Figure 5**, in the upper part of the histogram, shows the number of bridges tested and the number of X-rays taken over a particular 5-year interval. At the same time, the number of internal structural cracks in connecting welds is given. These cracks were discovered on 437 X-rays. They constitute 2.8% of the total number of welds tested, equaling 15,875 units. This number includes 10,507 X-rays on butt joints in tensile components and the remaining 5368 X-rays on compress components. Simultaneously, the lower part of the histogram gives the number of welded joints tested over given 5-year intervals.

**Figure 6** shows the proportional and numerical specification of hot cracks detected in bridge structures for given 5-year intervals of construction. Apart from one crack from 1974, the remaining cracks were ascertained in bridges constructed before 1960. According to Eurocode 1993-1-9 for the design of steel structures, such cracks do not

**Figure 5.** *Numerical specification of the bridges and welded joints tested.*

*Quality and Fatigue Assessment of Welded Railway Bridge Components by Testing DOI: http://dx.doi.org/10.5772/intechopen.104439*

#### **Figure 6.**

*Specification for bridges and joints with hot cracks.*

exclude structures from service. The upper parts of the histogram (**Figure 6**) show the proportional and numerical specification of bridges with internal cracks in welded butt splices. Of note is that the majority of cracks were found in the oldest historical bridges from the years 1936–1940. For the seven bridges from that period tested, cracks were discovered in six structures, which constitute 85.7%. They were discovered on 124 welded butt splices from the general lot of 696 pieces tested.

Similar unfavorable test results were obtained during examination of the bridges constructed over the years 1946–1950. Cracks were found in 18 structures (37.5%) on 270 X-rays (5.5%).
