PSI - Issue 22

Carlos D.S. Souto et al. / Procedia Structural Integrity 22 (2019) 376–385 Author name / Structural Integrity Procedia 00 (2018) 000–000

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4.1. User input data tab

In the user input data tab, the user must specify the following parameters:

1. Stress type, σ or τ : This parameter will tell FDT if it is dealing with direct or shear stress ranges. 2. Slope of fatigue strength curve, m : This parameter will tell FDT to use 1 or 2 slopes for the fatigue strength curves. The user can also choose between the established slope values of the Eurocode 3 or input custom values for the slopes. 3. Partial factor for fatigue strength, γ M f : This parameter is a safety factor. The specified detail category will be divided by this parameter, so the damage calculation is done on a weaker detail, making the calculations for the original detail safer. The user can choose between the established assessment methods and consequences of failure of the Eurocode 3 or input a custom value for the safety factor. 4. Detail category, ∆ σ C : This parameter is the numerical designation given to a particular constructional detail. The detail category indicates the reference fatigue strength in MPa. The user can input a detail category from the Eurocode 3 tables as well as a custom value. FDT will also output the fatigue limit, ∆ σ D , and the cut-o ff limit, ∆ σ L , which later will be used in the fatigue damage calculation. 5. Partial safety factor for fatigue loading, γ F f : This parameter is a safety factor. The calculated stress ranges will be multiplied by this parameter, so the damage calculation is done on harsher stress ranges, making the calculations for the original ones safer. 6. Number of repetitions: This parameter is the number of times the stress-time history is repeated during the lifetime of the constructional detail. 7. Stress-time history: The user must finally input the stress-time history of the constructional detail, comprised only of peaks and valleys. However, as mentioned previously, FDT can convert any spectrum data into peaks and valleys if necessary.

4.2. Rainflow counting algorithm tab

In this tab the user will be able to:

1. Execute the rainflow counting algorithm based on the loaded stress-time history. 2. See the algorithm results. 3. Easily copy the results into the Windows R clipboard, so that they can be used elsewhere if the user so desires.

4.3. Fatigue damage calculation tab

In this tab the user will be able to:

1. Execute the calculation of the fatigue damage using the Palmgren-Miner rule based on all the user inputs. 2. See the calculation results. 3. Easily copy the results into the Windows R clipboard, so that they can be used elsewhere if the user so desires. 4. Check if the Fatigue Damage Accumulation, D , is less than or equal to the inverse of the Design Fatigue Factor, D FF . This factor can also be seen as another safety factor.

5. Case study of fatigue damage assessment

In order to demonstrate the capabilities of FDT, a case study on the Va´rzeas railway bridge (Fig. 6) is considered. For this bridge, a critical detail was identified and the stress-time history for its most critical point was obtained through numerical analysis (Boavida-Barroso, 2019) considering the fatigue load defined by the type 5 locomotive hauled freight train, adapted from Eurocode 1 EN1991-2 (2004) and shown in Fig. 7. It was verified that the maximum fatigue damage value occurred for a train speed of 80 km / h considering a vibration mode with a frequency of 60 Hz (Boavida-Barroso, 2019), for this case the stress-time history used in FDT is shown in Fig. 8. For the chosen