It is accepted that sliding or friction base isolation systems effectively protect structures subjected to severe earthquakes. Precise modeling of the sliding connection is, however, still difficult since various parameters influence the friction coefficient. Simplified models, such as those based on a constant friction coefficient, are convenient to understand the behavior of sliding structures and to identify general trends. However, this article shows that for final structural designs (and in particular if the building enters in the nonlinear range) these trends should be used carefully. The purpose oí the article is to discuss the general behavior of structures supported on sliding connections and to describe a simple numeric model to take into account variations in the friction coefficient. The numeric model enables to represent complex force-displacement relationships for the sliding bearings. The model is used to perform a preliminary evaluation of the influence in the response caused by changes in the friction coefficient for elastic and elasto-plastic structures. The variations in the friction coefficient are obtained from experimental testing for a class of teflon-based connections.