The relationship between seismic characteristics, known as the intensity measure, and the structural demand parameter of the structure, called the seismic demand model and has been assumed to be linear on a logarithmic scale in classical studies. Because of the critical role of the seismic demand model in reliability analysis of structures and reducing uncertainties, in the present study, the performance of different demand models is compared to the simple linear model. Different criteria such as sufficiency, efficiency, and correlation are considered in this analysis. The effect of different scalar or vector-valued intensity measures, pulse-like earthquake records, structural damage level, structural demand parameters, and height of structures on the performance of the demand models with the help of relative entropy concepts is estimated. The results indicate the necessity of nonlinear demand models, especially at high structural damage levels. Therefore the second-order demand model is more suitable due to simplicity rather than other nonlinear demand models.
