Vibrations in a Built Environment : Prediction and Reduction

Sammanfattning: Vibrations in a built environment can exceed the requirements for sensitive equipment in a building or can cause annoyance to residents. Hence, there is often a need for reducing such vibrations. The vibrations can originate from ambient sources such as motorway traffic, or from internal sources such as people walking inside the building. Disturbing vibrations can be reduced by reduction measures. Vibration-reduction measures can be evaluated numerically, with for instance the finite element method, to avoid construction of expensive mock-ups. In the thesis, large finite element models involving several physical domains (e.g. road, soil, bedrock, and building parts) were developed to study the effect of vibration-reduction measures.Ground vibrations can be reduced by installing a wave barrier between an external source and a receiver. As concluded in the thesis, an empty barrier (i.e. a trench) installed in the soil has the ability to reduce the ground-vibration level by approximately 60%. If the barrier contains a solid material, however, the level of reduction is reduced to approximately 30%. At long distances, at around 500 m and longer, from the vibration source, an amplification in vibration is observed. At such distances, moreover, the ground motion follows the motion of the bedrock. Another example of a wave obstacle that is studied in the thesis involves shaping the landscape surrounding a building. The topsoil that is usually transported from the construction site can be used to construct hills and valleys that constitute the shaped landscape. However, this can result in anything from an appreciable reduction to an appreciable amplification in the ground-vibration levels, depending on how the landscape is formed. If constructed properly, the reduction in the level of vibration can reach approximately 35%. Vibrations from both external and internal sources can be reduced by modifying the properties of the concrete slabs and the soil underneath. The soil properties can be improved by mixing the soil with a binder, in order to stiffen the soil. Is is shown in the thesis that by using stabilised soil underneath a concrete slab, vibrations originating from motorway traffic can be reduced by almost 60%, and up to 80% for an internal pedestrian load. By using a time-efficient numerical model developed in the thesis, the effect by using different positions for the supports of a water-pipe system on vibrations transmitted to other parts of buildings was studied. Because frequency peaks can be avoided, a marked change of vibration characteristics can be achieved. A reduction of more than 60% in the transmitted vibrations was observed. The general methods and measures presented in the thesis are exemplified by the conceptual design process of the MAX IV Laboratory, a vibration-sensitive research facility. This laboratory exhibited the phenomena needed for selecting it as a comprehensive example case.