Assessment of Ground Vibration for Early-Stage Design
Abstract: Ground borne vibrations in urban areas can be caused by human activities such as railwayand road traffic, construction works and industrial manufacturing. These vibrations can playa significant role in human comfort and the disruption of vibration sensitive equipment inbuildings. The rapid expansion of cities and urban sprawl has created the need for the increasedconstruction of residential apartments. This often occurs within already built-up areas in order totake advantage of the existing transport infrastructure, such as train lines. The risk of detrimentaleffects from train lines should therefore be assessed at a design stage. This is particularlyimportant in many densely populated areas of Sweden, where the geological conditions (softclay above stiff bedrock) are susceptible to high levels of ground borne vibrations. The purpose of this thesis is to evaluate the influence of inertial soil-structure-interaction (SSI)on the dynamic response of a building by comparing the vibration characteristics of a buildingmodel with a rigid foundation to a model where pile foundation impedances are included, andto assess the suitability of this method in early design stage. This is performed by comparingthe dynamic response of a building model with a rigid foundation, to a building model withthe pile-group impedances considered. A case study in Stockholm, Sweden has been chosen torepresent a typical construction project in a densely populated urban centre in Sweden. A basesoil profile created from existing data provided by site investigations and pile-group impedancesare calculated. It is shown that these impedances can vary greatly across the frequency spectrum, and assuminga stiff foundation and adopting a single value for stiffness and damping is an inadequaterepresentation of the system, as SSI can have a significant influence on its dynamic behaviour.In particular, the impedances of the pile-groups are shown to be particularly sensitive tochanges in stiffness of the upper soil layers. A lower response was exhibited when consideringpile-group impedances when compared to a building model with a rigid foundation, with areduction of peak velocities and a slight shift in the eigenfrequencies of the dynamic responseof the building. However, a considerable increase in modal damping occurs. This highlights thesignificance of considering the impedance of pile groups, whereby both the dynamic stiffnessand damping noticeably affect the dynamic response of a building.
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