PSI - Issue 5

M.H. Hebdon et al. / Procedia Structural Integrity 5 (2017) 1027–1034 Liu et al. / Structural Integrity Procedia 00 (2017) 000 – 000

1033

7

0 10 20 30 40 50 60

a

b

10 20 30 40 50

0 10 20 30 40 50

L18

Tire

L18-0 L18-1 L18-2

L16-2 L17-2 L18-2 L19-2 L20-2

0

1

2

Center line

340

360

380

400

420

440

-10 0

0

100

200

300

400

500

0

100

200

300

400

500

Load step

Load step

Stress-time history (MPa)

Stress-time history (MPa)

Fig. 8. (a) Stress-time histories of connection L16-2 to L20-2; (b) Stress-time histories of connection L18-0, L18-1 and L18-2.

4.3. Results and discussion

Rain-flow counting was conducted to capture the stress ranges and number of cycles ( N s ) caused by a single truck. The fatigue lives in cycle of Connection L16-2 and L20-2 were calculated based on the Eq. 3, and those fatigue lives in year were further obtained. The calculated lives of those connections are more than 50 years except that the calculated life of L19-2 is only 44.8 years. It is indicated that the connection L19-2 is most vulnerable to fatigue damage. Furthermore, the N s is equal to 3 in those connections, inconsistent with the recommendation value (i.e. N s =1) in the Eurocode. The calculated process reveals that the fatigue category and N s have significant influence on the results. To study the influence of N s , the fatigue life of the connection L19-2 is further calculated, assuming that N s =1. The fatigue life of connection L19-2 is 134.86 years when N s =1, indicating the significant influence of the N s on the calculated results. Hence, the prescribed N s =1 is insufficient for the connection under/near the wheel tracking.

Table 1. Fatigue assessment results of Connection L16-2 and L20-2 Connection Category Δ σ e (MPa)

N s (cycle)

N (cycle) 3.523 × 10 8 3.229 × 10 8 3.157 × 10 8 2.692 × 10 8 3.884 × 10 8

T (year)

L16-2 L17-2 L18-2 L19-2 L20-2

80 MPa 80 MPa 80 MPa 80 MPa 80 MPa

19.37 19.94 20.09 21.19 18.75

3 3 3 3 3

58.7 53.8 52.6 44.8 64.7

5. Conclusions

This paper conducts fatigue life evaluation of critical details according to fatigue specifications given in Eurocode. According to the research in this paper, conclusions are drawn as follows: 1. Due to the complex configuration of the stringer-to-floor-beam connection, significant stress concentration and larger stress range exits in the stringer-to-floor-beam connection in the HLB. As the change in the connection between the chain and truss, the connections near the change parts of eyebar chains are most prone to fatigue damage under traffic load, especially the connection L19-2. 2. The fatigue category and N s have significant influence on the calculation of the fatigue life. It seems that the value N s prescribed in Eurocode is less conservative for the connection near the wheel tracking than that in fact. 3. To refer the need for a comparison of results between the most commonly used design codes available, taking into account that the original bridge was design using AASHTO.

Acknowledgements

The authors acknowledge the Portuguese Science Foundation (FCT) for the financial support through the post - doctoral grant SFRH/BPD/107825/2015. This work was also financial supported in a part by the Federal University of Minas Gerais and Teixeira Duarte SA. Special thanks are given to Prof. Tong Guo at Southeast University, China, for his professional guidance and valuable discussion in research process.