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., Kozák J./ Structural Integrity Procedia 00 (2018) 000–000

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Fig. 5. Rain Flow Matrix. Sixteen combinations of loads values.

For example, the combination in the J6 cell is counted once. The mean value of normal force is 24.57 kN and range is 56.62 kN (minimum is 32.05 kN, maximum is 81.19 kN). Subsequently, two equivalent stresses are obtained from the nonlinear calculation of the entire detail (see Fig. 6). The stresses across all nodes combine to determine the equivalent alternating stress.

(a) (b) Fig. 6. Results of equivalent stress (Δσ i ) (a) Combination J6 with maximal force; (b) Combination J6 with minimal force.

In analysing fatigue properties, it is possible to define the material in several ways. One possibility is using S-N curves that relate to the detail of the connection. Knowing the equivalent stress, the number of life cycles can be determined from the S-N curve. That value is the inverse value of fatigue damage. The real material properties are not known for the presented historical steel construction. Hence, as an example, the lowest S-N curve was chosen. For each of the 16 load combinations, the equivalent fatigue damages were obtained. This data has been summed and their result is reversed for the number of cycles to the structural element failure. The estimation of service life was considered with one cycle per day and 255 working days of the year (see Table 2).

Table 2. Service life summary. Part of connection

No. of cycles

Service life 315 years 683 years 259 years

Diagonal

80 515 174 216 66 006

Rivets Plate