The dynamic behaviour of civil engineering constructions is characterised by non-linear phenomena whose effects may be non negligible even in the presence of minor external excitations. The use of complex models, i.e. models that are able to describe with accuracy the dynamic behaviour of structures investigated by taking into account the hysteretic and degrading nature of the dynamic response, is justified in several applications. This paper investigates in depth the identification of damage in a steel-concrete composite, moment-resisting framed structure subjected to a seismic excitation reproduced by pseudo-dynamic testing. The structure is thought as a shear-type frame and the global interstorey behaviour -force-drift law is represented by hysteretic models. This work aims at applying to a real structure the time-frequency identification procedures that the authors developed for hysteretic systems; the model parameters are evaluated from instantaneous estimates of the time-varying coefficients. The instantaneous estimation, based on optimization techniques, is made possible through the temporal localization of frequency components.