For the fatigue design of aluminum structures, most applicable international codes specify fatigue-resistance (S-N) curves with slopes that vary, depending on the detail category. This complicates the selection of appropriate damage equivalence factors for use in highway bridge applications. The existing codes also differ in their treatment of high cycle fatigue, with single-slope S-N curves specified in some cases and multislope curves specified in others. In this paper, a recent investigation conducted to examine the fatigue behavior of aluminum welds under in-service highway bridge loading conditions is summarized. Specifically, calculations performed to establish damage equivalence factors for aluminum for use with the AASHTO and Canadian Standards Association (CSA) CAN/CSA-S6 codes are first reviewed. Following this, small-scale fatigue tests of aluminum welds under simulated highway bridge loading conditions are described. A fracture mechanics model is then validated by comparison with the test results and used to perform simulations encompassing a wider range of loading conditions. On the basis of this work, the adequacy of the current design provisions is discussed and possibilities for further extending the employed methodology are identified.

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<p>The use of cable stayed structures for long span bridges gained popularity in the late 20th century with the development of advanced construction materials and equipment, and advancement of sophisticated structural design and modelling capabilities. There are many light rail transit (LRT) cable-stayed bridges in use today. Due to the repetitive cycling loading from passage of similar trains, the potential risk of fatigue-induced damage to stay cables is significantly higher for LRT bridges than roadway bridges. As LRT bridges carry heavier trains and provide increased levels of service, the fatigue induced damage to stay cables and its impact on the remaining service life has been frequently raised by transit authorities. This paper presents a recent study completed on assessing fatigue induced damage to stay cable for a LRT bridge including numerical analysis, processing of historic and future train data, and field investigation of the bridge’s response.</p>