Issue 45

D. Peng et alii, Frattura ed Integrità Strutturale, 45 (2018) 33-44; DOI: 10.3221/IGF-ESIS.45.03 36 bridge and wait for a further 5 years or so until the sensors/samples themselves reach the steady state corrosion rate that the bridge is seeing. You need answers much sooner. The advantage of the AASHTO bi-linear approach is that once the bridge is behaving such that the metal loss versus time curve is on the line AB, see Fig.1, you know the long-term corrosion rate without having to monitor the bridge for years. For bridges this can be done in the order of four to twelve months using electrical resistance corrosion sensors [2]. A steel electrical resistance corrosion sensor was used to measure the metal loss in Bridge 62 at Kilmore East which is inland in Victoria, Australia. Fig. 1 substantiates the NCHRP and AASHTO formulation and the advantage gained in real time monitoring of a rail bridge to obtain the long-term corrosion rate. The steady state corrosion rates determined in this test is 0.024 (mm/year). These rates are consistent with those documented in [25]. Figure 1: Measured thickness loss at East Kilmore in Victoria. The results of this study support the AASHTO standard for the loss of metal seen by steel bridges. As such the AASHTO bi-linear relationship between metal loss and the time in service provides a simple method for estimating the corrosion rates associated with aging structures. O PERATIONAL LOAD SPECTRA s part of the corrosion measurement program mentioned above the strain (load) spectra was also measured. Bridge 62 in East Kilmore saw passenger trains, including trains pulled by N Class locomotives, Sprinter carriages, ore trains. Armed with this information and details of the number of trains per week, see Table 1, the load spectrum associated with the bridge can be determined. Train Type Loco Weight Wagon Weight No of Wagons No per Week Total Wt/Week N Class Passenger 118 60 5 14 5852 Sprinter 60 2 14 1680 Ore Train 128 100 20 7 14896 Table 1 : Data on trains using UP line over Bridge 62. F ATIGUE CRACK GROWTH WITH CORROSION EFFECT MODEL rmed with a knowledge of the da/dN versus ΔK behavior of bridge steels, the load spectrum and the steady state corrosion rate we are now in a position to assess the combined effect of corrosion and fatigue on the remaining life of a bridge. A A