Lightweight floor system for vibration comfort

A shorter functional lifespan of buildings due to increased rate of change of technological advances as well as the increased awareness of environmental impact of the building industry are some of the challenges facing the current building industry. The approach to address these challenges, that received a big audience in the Netherlands, was the IFD or Industrial, Flexible and Demountable way of building. Of the three pillars of this way of building the part that addressed flexibility was most successful. In more recent years IFD has been succeeded by sustainable building with the focus shifting more to preserving the environment as well as continuing effort to increase functional lifespan of buildings. Looking at developments regarding floor systems, using a method developed in this thesis, innovations can be observed that comply with these strategies. Often these innovations involved incorporating hollow spaces in the structural layer. This allowed for an increase of flexibility during the lifespan as well as reducing the amount of material used. But this reduction in material use resulted in an undesired floor property, namely poor vibration comfort. Vibration comfort is a relatively undervalued floor characteristic in the current building industry. Vibrations in floor systems can be caused by vibrating equipment but also by walking people. Some effort has been made in Europe to define methods specifically suited to predict vibration comfort in floor systems. The One-step RMS90 method is used in this thesis to quantitatively analyze vibrations in floor systems. Vibration comfort can be influenced in multiple ways that can be classified in passive or active methods. Active methods include systems such as tuned mass dampers or active dampers. These can be considered to be additions to a floor system that inherently lacks good vibration comfort. The main objective in this thesis is to develop a passive method that provides a floor system inherently with good vibration comfort. The research presented in this thesis into passive methods of providing good vibration comfort is divided into a couple of steps with increasing complexity using the most suitable research technique. For this a floor system is characterized by a single span beam of a unitary width, which is adequate to describe most current floor systems. Each step is concluded with guidelines for enhancing vibration comfort. The first step is to analyze the influence of the properties of just a single beam as well as the support properties on the first mode frequency, an important vibration characteristic. A mathematical function is derived that calculates up to the fifth mode frequency with good accuracy. Subsequently an analysis is performed on a single beam as well as a set of up to five beams. Beam properties as well as their structural geometrical layout of how they are connected to each other are varied. For this a finite element model is used. The results are used to calculate the vibration comfort using the One-step RMS90 method and subsequently analyzed to define methods that increase vibration comfort. Based on the results of these two theoretical approaches, a number of concepts are defined. The concepts aim at improving properties such as the first mode frequency and vibration damping. Due to the complexity of these concepts these are evaluated experimentally to determine the most promising concept. It has been found that a constrained layer design, which includes a damping layer, provides for a method of improving vibration comfort in a consistent manner by increasing the damping capacity. Utilizing such a design always results in increased damping but a mathematical description is needed to describe how to optimize the benefits of such a design. The mathematical description of the constrained layer design is developed and a parameter study is presented to find design guidelines for optimizing damping. Finally the guidelines provided in the various research steps are used to define a conceptual floor structure to optimize vibration comfort. Also improvements for some existing floor systems are provided. This final part is set up in such a way that it allows for further efforts to optimize designs by others.