The seismic damage analysis of steel frames based on the use of global evaluation indices is addressed. A general procedure is proposed aimed at estimating the degree of damage induced by severe earthquakes in structures not supplied with monitoring systems. Special reference is made to the Park-Ang, McCabe-Hall, and plastic fatigue indices. The procedure is characterized by a form of automatic calibration of the free coefficients contained in the expressions of these indices. This allows one to constrain the arbitrariness in the coefficient choices, representing the greatest source of uncertainties for practical damage field assessment. Story stiffness degradation and permanent interstory displacements are assumed as the a posteriori measurable quantities upon which the reliability of the computational predictions supporting damage estimation are checked. The suitability of this procedure as well as of the considered indices for seismic damage characterization are discussed with reference to two case studies, represented by one shear-type and one concentrically braced, two-story plane steel frame, experimentally tested to failure.
