New energy-based methodology to characterize nonlinear seismic response

The quantitative identification of limit states through damage indices is of utmost importance in seismic design. Among others, energy-based indices have consistently demonstrated great solidity and reliability in predicting the collapse potential of structures under earthquake. The existing proposals, however, have not a sound mechanical basis and rarely take into account how seismic energy is transmitted. A novel metric for the characterization of structural damage is presented in this work with the aim of overcoming approximations or arbitrary interpretations related to the definition of damage limit states. Based on geometric and physical principles, the nonlinear response of the structural systems is described by two parameters that define the damage state and the internal variation of the structural response. These two physics-based variables are next combined to develop a measurable space accounting for both dissipated energy and power. The proposed methodology is generalized and validated on a set of experimental tests. Coherent limit states (namely, elastic, severe damage, and collapse limit states) are identified based on experimental evidence as the instants in which significant variations of the structural response occur. The proposed methodology has proven to be stable and consistent, demonstrating its effectiveness regardless of the specific material properties and the seismic action. A comparison with some of the most used damage indices was then conducted in order to show the effectiveness of the proposed methodology.