Issue 42

Correia et alii, Frattura ed Integrità Strutturale, 42 (2017) 136-146; DOI: 10.3221/IGF-ESIS.42.15

the BS7910 standard [3] is indicated for current structural steels. This standard use the mean curve 2 S  to describe the design curve for the fatigue crack growth rates. In Tab. 1 the C and m parameters are presented for all materials from Portuguese metallic bridges and also the standard deviation, S , which is used to define the mean FCG curve 2 S  . This design curve is important to be used in rehabilitation studies of historical bridges (to analyse the fatigue residual life of structural details). The design FCG curve proposed by BS7910 standard when compared with each material from the Eiffel, Luiz I and Fão bridges revealed not be representative of these materials. However, when compared to the experimental FCG data of the Pinhão and Trezói bridges, the design FCG curve proposed by BS7910 standard, seems to be more representative of these old materials. It should be noted that the materials of the Pinhão and Trezói bridges are more recent when compared to the other materials. In the Fig. 8, the statistical analysis using the mean FCG curve 2 S  applied to the experimental data for all materials from ancient riveted bridges proved to be reasonably satisfactory, however the use of the mean FCG curve 3 S  to cover all experimental data is suggested. The slopes of the FCG curves of the materials from the Eiffel, Luiz I and Fão bridges revealed to be similar, indicating the tendency exhibited for old materials. However, the slopes of the FCG curves for the materials from Pinhão and Trezói bridges exhibited a consistent behaviour with the slope of the design FCG curve proposed by BS 7910 standard [3]. The statistical analysis applied to FCG data proved to be efficient.

Material

S

C

* C

* m m 

17.614 

0.3463

4.69

Eiffel

17 1.199 10  

Luiz I

19.543 

0.2548

5.50

20 9.243 10  

4.03

0.2378

Fão

15.126 

15 2.237 10  

0.1082

3.62

Pinhão

14.539 

15 4.757 10  

14.278 

0.1317

Trezói

3.54

15 9.660 10  

13.998 

0.2967

3.47

All materials

14 3.940 10  

/ da dN in

/ mm cycle

Table 1 : Constants of the mean FCG curve for all materials from the Portuguese old metallic bridges, with

1.5 . N mm  .

and K  in

1.0E‐8 1.0E‐7 1.0E‐6 1.0E‐5 1.0E‐4 1.0E‐3 1.0E‐2 1.0E‐1

2T1 (R=0.1) 2T2 (R=0.1) 2T3 (R=0.5) 2T4 (R=0.5) 2L1 (R=0.1)

[mm/cycle]

Mean curve ‐ Exp. Data mean FCG curve + 2S mean FCG curve ‐ 2S Mean curve + 2S: Stage B; BS7910 Mean curve: Stage B; BS7910

100

500

1000 1500

[N.mm ‐1.5 ]

Figure 3 : Statistical analysis of the FCG data for the material from the Eiffel bridge.

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