On the prediction of low-cycle fatigue in steel welded beam-to-column joints

This paper presents a phenomenological criterion for crack initiation based failure prediction of steel structural components exposed to low-cycle fatigue loading. The criterion was established on the basis of available effective damage concept and associated two-parameter criterion. First, experimental cyclic test results on rib stiffened and cover plate stiffened beam-to-column joints are presented, which were used subsequently to verify the numerical model employed for the development of the proposed crack initiation criterion. The two-parameter criterion in which total accumulated plastic strain and stress triaxiality h were adopted as mechanical parameters that control the LCF cracking was applied to define a new damage curve. Several validation examples are presented to demonstrate the capability and accuracy of the proposed methodology for low-cycle fatigue life prediction. The applicability aspect of the proposed cracking criterion is further presented in terms of systematically defined complementary numerical analysis on welded stiffened beam-to-column joints focused on exploring any potential adverse beam member type and size effects on the cyclic response of the full-strength joint configurations. To this aim a set of eight practically applicable I and H European beam profiles was considered for the joints. All the analysed stiffened joints subjected to cyclic loading simulations possessed sufficient degree of overstrength to allow for the development of the full beam plastic rotation capacity. However, from the subsequent analysis important difference in fatigue behaviour between RS and CP joints was found.