This paper presents the development of a lumped-parameter model of multistory framed shear buildings supporting rigid blocks with the possibility to slide. After favorably comparing with results from finite-element analyses and shake table tests, the model was used to assess design provisions in regard to the treatment of live load as seismic weight. It was found that using the minimum live load percentage in current design standards may lead to unconservative drift estimates for buildings supporting heavy and nearly permanent live load objects and structures that are (1) designed for higher R values, (2) located in regions of low-to-moderate seismic risk, or (3) base isolated. Results from a parametric study led to a design expression that allows determining the portion of the expected live load that is effective as seismic weight on the structure as a function of the object/floor interface's friction coefficient and the maximum floor acceleration of the building alone. The adequacy of the design expression was confirmed through three-dimensional finite-element analyses of two- and four-story buildings supporting live load objects that could slide.