Seismic damage assessment and failure criteria for steel members and connections

An experimental research was carried out to investigate the seismic behaviour of steel beam-columns, as well as of connections with particular emphasis to beam-to-column ones. Several full scale specimens were submitted, in a multi-specimen testing program, to constant amplitude displacement histories, in order to develop a cumulative damage model and establish possible classes of fatigue resistance for members and connections. Variable amplitude tests were carried out in order to verify the validity of the proposed model. It is shown that the S-N lines given by Codes for high cycle fatigue can be used for interpreting the low cycle fatigue behaviour of steel members and connections. Miner's rule can be adopted, together with the previously defined S-N curves and with a cycle counting method to define a unified cumulative damage model valid for both high and low cycle fatigue. A general failure criterion is proposed, which considers the actual energy dissipation through plastic deformations.