# Damping Assessment of Lightweight Timber Floors Under Human Walking Excitations
## 1 Introduction  
Lightweight timber floors are attracting considerable interest in developing countries because of their advantages in terms of sustainability and construction speed. Among the different structural systems in buildings, floors are the only part with which human occupants are in constant physical contact. Therefore, this construction component could become a common source of complaints from the users, generated by the deflections and excessive vertical vibration of the floors while walking on them [1]. This issue, which is becoming more recurrent in diverse construction contexts, has generated a sustained increase in experimental research associated with the dynamic serviceability of timber floors [2]. Damping is one of the most influential factors in the human perception of transient vibration in a timber floor system [1]. This is because damping is an intrinsic property of structural systems that influences oscillation amplitudes and the rate of decay under forced and free vibrations, respectively [1]. Therefore, knowing the level of damping of a timber floor is an essential aspect for structural designers since vibrations tend to be more tolerable in floors that have higher damping [3]. On timber floors, damping comes from two primary sources: the material damping (due to the internal wood anatomy and its defects, such as knots and internal cracks) and structural damping (due to friction in the structural joints and friction between structural and non-structural elements) [3].Under human walking operational conditions, damping can be generated due to the combined effect ofdifferent small sources of non-linearity, such as joint friction, interaction between structural and non-structural elements, and the effect of the floor content. Hence, operational damping is not only generated by the intrinsic modal damping of the structure, but also because of all these other energy dissipation mechanisms. In terms of the structural performance, operational damping is more interesting to analyze than intrinsic modal damping, because this is the effect perceived by people. From the above, it can be deduced that it is not realistic to define a single damping value that is representative of all timber floors. Therefore, each type of construction must be analyzed separately, since any difference in the construction technique or even in the workforce quality could generate different levels of damping [3]. Several studies have been published on damping ratio estimations for different kinds of timber floors constructed in laboratory-controlled conditions. Firstly, investigations focused on studying timber floors that allowed span lengths between 3 m and 5 m to be reached. The floors were generally built with glulam beams [3], an I-joist [4], and a metal web jost [5; 6], nailed, screwed, or glued to particleboard or plywood flooring. The damping ratios obtained in these floors had values from 0.82% to 4.78% for the first resonant mode. Subsequently, research focused on studying timber floors that could reach greater span lengths, between 6 m and 8 m. In this way, studies were carried out on timber floors built with laminated veneer lumber beams (LVL) [7], and cross-laminated timber (CLT)-concrete composite slabs [8]. Damping ratios between 0.52% and 1.29% for the first resonant mode were found for these floors. Most of the investigations mentioned above considered idealized support conditions for the floors and did not take into account the interaction with typical in-situ non-structural elements, such as ceilings on the floor's underside and partition walls. On the other hand, in the last decade, only a few studies have focused on damping ratio estimations for in-situ timber floors. Initially, some researchers analyzed the damping ratios for traditional timber floors in the context of elementary schools [9] and multi-family buildings [10].