Structural Damage Characterization via Energy-Based Limit State Definition

In seismic design the concept of damage limit state is the basis of Performance Based Earthquake Design. Numerous proposals have been presented over the years in the literature, almost entirely based on the displacement method. In more recent years, new methodologies based on an energetic approach have shown greater solidity in identifying the collapse, which is essential in order to be able to build collapse fragility models. However, there is a lack of a physical interpretation of the phenomenon of capacity that allows a definition that can be universally shared and applicable to different materials and structural models. A new metric is presented aimed at the characterization of the structural capacity with the aim of overcoming the uncertainties related to the definition of the concept of the damage limit state, through a theory that is clear and coherent, based on geometric and physical principles, and which avoids approximations or arbitrary interpretations of the physical phenomenon to be characterized. The theory was modeled on a simple one degree-of-freedom oscillator in Opensees with the Modified Ibarra-Medina-Krawinkler Deterioration model, to then be verified through the construction of a case study obtained on experimental data from cyclic tests, conducted with different materials and models. Limit states are indicated in relation with the displacement force method.