Abstract | Composite steel-concrete floor systems are widely used in modern construction for achieving long-spans with a low number of intermediate columns. The design of such slender and lightweight floor systems is typically governed by the serviceability limit state requirements, associated with deformations, human comfort perception, and vibration tolerances. To guide designers through the process of delivering floors that are not prone to human-induced vibrations, and hence imposing a feeling of discomfort to their users, a number of design guidelines of variable complexity have been developed in the past few decades [1,2]. In their simplest form, such guidelines adopt several deterministic assumptions regarding the floor damping, the imposed loads, the connection rigidity under service loads, the step frequency, the footpath and the human weight. In this study, sources of uncertainty are discussed. A numerical grillage-based floor model is also presented, that could be utilised for extracting the needed engineering demand parameters for undertaking an assessment of such floor systems when subjected to walking-induced vibrations.