Issue 45

D. Peng et alii, Frattura ed Integrità Strutturale, 45 (2018) 33-44; DOI: 10.3221/IGF-ESIS.45.03 37 Failure due to Material loss (Corrosion) The bending couple M applied to the section of interest creates normal stresses in the cross section, while the shear force V creates shearing stresses in that section. Corrosion of steel bridge girders will be a maximum where electrolyte can “wick” between the transom and the girder compression flange or where electrolyte is trapped by some other means. In general, the worst case scenario involves a loss of material from the web, top flange and bottom flange. A graphical representation of the corroded I beam is provided in Figure 3. Using the equation for outer flange fiber stress in beams subject to bending:   / Q My I (2) where σ is the stress, M is the applied Moment, y the distance from the beam neutral axis to the extreme flange fiber and I is the Moment of Inertia about the neutral axis, a spread sheet can be raised which tabulates reducing flange thickness due to corrosion and consequential increased girder flange stresses. The limits are the as-new girder measured stress and the material yield stress. Let us define the normal and shear stress at point Q1 as shown in Fig. 3 as σ Q 1 and τ Q 1    1 ( ) / Q M y t I (3)    1 ( ) / (2 ) Q H t BtV bI (4) With this notation the maximum principle stress at point Q1 is:                2 2 1 1 1 1 1 ( ) 2 2 Q Q Q Q (5) Therefore, the maximum stress in the flange is given by         1 1 , ( ) Q Max Q (6) If the measured corrosion rate for bridge steel I beam is ξ (mm/year), the maximum stress in I beam σ is function of the corrosion rate ξ . Figure 3: Graphical representation of the corroded I beam. Failure due to the combined action of corrosion and fatigue Since, on tension dominated surfaces, the life of the corroded steel bridge is a strong function of both the corrosion rate and the assumed initiating (inherent) crack size this paper addresses the interaction of combined corrosion and crack growth on remaining life. In this analysis the stress intensity factors were computed as outlined in steps b) and c) in Section 1. For