PSI - Issue 5

Hołowaty J. et al. / Procedia Structural Integrity 5 (2017) 1035 – 1042 Wichtowski and Hołowaty. / Structural Integrity Procedia 00 ( 2017) 000 – 000

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2.2. Fatigue assessment procedure

If a bridge passes the general assessment procedure for immediate resistance (design or service), then a fatigue endurance procedure is carried out. This procedure is usually decisive in calculating the remaining residual service usability of a bridge. The full fatigue assessment procedure advised by the JCR recommendations is given in Fig. 1. This is a four-phase algorithm procedure for existing steel bridges. The aim of phase I is the analysis of existing documentation, a detailed inspection of the bridge and an initial assessment of its fatigue safety level according to Eurocodes EN 1991-2, EN 1993-1-9 and EN 1993-2 [Nussbaumer et al. (2011)]. In phase II the bridge's ‘safe life’ is determined using the Palmgren -Miner rule for linear cumulative damage calculations following initial measurements and tests [Wichtowski (2002)]. These data are concerned with actions, the structural model of the bridge and its material properties. Phase III includes activities using specific procedures and tools, such as:  Fracture mechanics methods to assess fatigue endurance,  The probabilistic method to assess the influence of basic parameter variability on fatigue endurance,  Quality testing by NDT methods. Where the phase I-III assessments give negative results, it is necessary to introduce remedial measures and/or repair works, which are defined in phase IV. These measures may be the intensification of inspections, the introduction of permanent monitoring, a reduction in weight and volume of vehicles, strengthening or closing the bridge, or demolition. The European methodology for the durability assessment of existing bridge structures here presented is becoming highly important in test results for butt welds on operating railway bridges. In 22 % of the welded bridges built from 1936-1975 in Poland which were assessed, internal cracks in the welded butt joints were found. The analysis of the joint behaviour over long-term operation described in this paper allows for the practical verification of the usability of European fatigue recommendations in the assessment of durability in railway bridges with welding imperfections. From 1954-1990 radiographic tests were carried out on welded butt splices in the main girders of 155 bridges, including 125 plate girder and 30 truss bridges. In Fig. 2, the number of bridges tested which were constructed over particular five-year periods and the number of radiographs taken are shown. The upper histogram shows the number of bridges tested and bridges with girders which have welded butt splices with cracks. The bottom histogram shows the number of joints tested on bridges built in subsequent five-year periods from 1936 to 1975. Cracks were discovered in 34 bridges (21.9 %) on 437 radiographs. 3. Quality of welded butt splices in the oldest railway bridges in Poland

Fig. 2. Numerical specification of bridges tested and bridges with cracks, along with joints tested.