PSI - Issue 13

Petr Lehner et al. / Procedia Structural Integrity 13 (2018) 1539–1544 Lehner P., K ř ivý V., Krejsa M., Pa ř enica P., / Structural Integrity Procedia 00 (2018) 000–000

1542

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2.2. Stochastic model of the load history In determining the appropriate probability distributions of input parameters, account was taken from estimation of the by the operating technician who has many years of experience with the operation of the attended warehouse. Properties shown in Table 1 were determined from the detailed description of one shift.

Table 1. Summary of input parameters in the stochastic analysis. Description of input parameter

Distribution of shift history

Value

Distribution type

Actual crane weight

257.25 kN

Constant Constant Constant Constant Uniform Uniform Uniform

Crab weight

71 kN

Number of cycles during one working day

140

50% 40% 10%

0 kN

0 - 50 kN 50 - 80 kN 1.9 - 16.2 m

Load weight distribution

Crab position

100%

Load history was generated for the selected time unit using Monte-Carlo simulations, in this case, for one shift. This simulation can replace direct measurement, taking into account the stochastic character of the input quantities, and the professional estimation of the operator. Amplitude of load history was obtained by combining reactions and influencing line on the selected diagonal. Since the number of values was in the order of tens of thousands, it was necessary to proceed to articular sorting. Due to this, the algorithm contains the searching of amplitude local maximal and minimal values (see Fig. 4). Original data from simulation contains about 60 000 values. After sorting, it's about 600 values. The resulting outputs were used for determination of the variable stress in the analysed details and for stochastic estimation of the residual life of the structure in the third part of analysis.

x 10 4

20 40 60 80

-40 -20 0

N o r m a l f o r c e s [ k N ]

0

50

100

150

200

250

300

350

400

450

500

550

The save records (maximal and minimal values) [-]

Fig. 4. Non-constant amplitude load history data for one of the diagonal from the structure at one work shift after searching for maximum and minimum amplitude values.

2.3. FEM model of diagonal with regard to fatigue The third part of the analysis was prepared in Ansys Workbench software. The FEMmodel of the analysed diagonal connection which consists of a diagonal, gusset plate and rivets, was prepared. Important factors were the introduction of loads and material characteristics. The program contains a fatigue module that allows sorting the values of stress variables by Rain Flow method. If a user inserts the original data, thousands of information must be processed, which is very time-consuming. Due this, data sorting was used as described in the previous paragraph. This has greatly accelerated the process. The software module prepares the Rain Flow Matrix, including mean values and normal forces range. The matrix acquires data of maximum and minimum values of normal forces, represents the number of these peaks, and creates a load combinations for the 3D model (see Fig. 5). In this case, the matrix contains 16 combinations with non-zero values. Currently, each combination is calculated separately.