Sensitivity of human-induced vibrations and comfort analysis to partially rigid STS joints in timber-to-timber composite floors

The study of floors vibration serviceability represents a well-known challenging task and has a critical role in comfort analysis, assessment and optimization of pedestrian systems in general. To this aim, several consolidated and/or simplified tools are available in the literature to address the most important aspects. In practice, however, most of assumptions for the analysis and verification are based on the use of rough mechanical models of joints and connections, which have indeed a primary role especially for composite floors. In this paper, the attention is given to timber-to-timber floors with inclined self-tapping screws (STS), and a parametric Finite-Element (FE) numerical investigation is carried out by taking into account conventional walking parameters and a case-study timber-to-timber composite beam, well representative of a one-way wooden floor. A major advantage for structural and pedestrian modelling stages is taken from previous literature efforts, while large attention is spent for the structural analysis and vibration serviceability assessment as a function of the STS mechanical parameters, first of all their secant stiffness. Comparative linear modal and non-linear time history analyses are parametrically carried out and addressed towards limit mechanical configurations, in terms of vibration frequency considerations, as well structural response and comfort assessment, based on classical performance indicators. The parametric numerical results are further discussed based on simplified methods provided by selected design standards, with a critical analysis of the effects due to the partial joint rigidity and of the floor sensitivity to joint features, both in terms of structural safety and comfort for similar systems.