Macromodeling of Crack Damage in Steel Beams Subjected to Nonstationary Low Cycle Fatigue

This study proposes a model of crack initiation and propagation in steel beams subjected to ultralow cycle fatigue. The model can be included in the general framework of lumped damage mechanics. A state variable called damage is introduced for each plastic hinge and can be related to the extension of the crack in the real structural component. The damage evolution law is based on the Manson-Coffin law, the Palmgren-Miner rule and two new concepts: the instantaneous plastic amplitude and a crack-driving variable. The model also describes crack closure effects using the unilateral damage assumption. It was validated by the numerical simulation of tests of steel beam-column connections subjected to cyclic loadings with constant and variable amplitudes, as reported in the literature. Advantages and limitations of the model are discussed for wider applications on the damage simulation of steel frame systems subjected to mechanical overloads, typically earthquake loading.