Numerical Analysis of Traffic-Induced Vibration

Abstract

Vibrationer fra trafik i bymiljøet kan belaste de omkringliggende bygninger og genere beboere. Ændringer af vejbelægning eller etablering af fartbump har i visse tilfælde vist sig at skabe uhensigtsmæssige vibrationer eller i specielle tilfælde forårsaget skade på bygninger. De nuværende metoder til at estimere belastningen fra trafikvibrationer baserer sig i høj grad på empiri og er relativt usikre. I litteraturen findes flere eksempler på, hvordan trafikvibrationer og disses indvirkninger på bygninger kan modelleres numerisk. Der ses dog ikke nogen konsensus omkring metoder for at opstille disse modeller, samtidig med at usikkerheden i modellerne er relativ stor. Dette afgangsprojekt med titlen Numerisk Analyse af Trafikinducerede Vibrationer omhandler derfor opstillingen af en koblet dynamisk finite element model med køretøj, vej, jordlegeme og bygning for beregning af vibrationer fra trafik. En plan finite element model af et jordlegeme med absorberende randbetingelser opstilles med en bygning modelleret som en toetages rammekonstruktion, hvor fundamentet er sammenkoblet med jorden. En generisk køretøjsmodel opstilles, hvor både hjul og affjedringssystem modelleres med et diskret fjeder, dæmper og masse system. Vejbelægningen kan opbygges som enten en flad overflade med flere typer af fartbump, konstrueret efter Vejdirektoratets anvisninger eller som en stokastisk model af en brostensbelægning. Grænsefladen mellem vejbelægning og jordlegeme opbygges af bjælkeelementer, som understøttes delvist interfaceelementer og Kelvin-understøtninger. En central del af projektet omhandler koblingen mellem køretøj og jordlegeme og mellem jordlegeme og bygning. Interaktionen mellem køretøj og jordlegeme evalueres i tidsdomænet ved hjælp af tre forskellige fremgangsmåder: en dekoblet, en eksplicit og en implicit metode. Interaktionen mellem jordlegeme og bygning modelleres ved at koble bygningens fundament sammen med jordlegemet. Parametrene der indgår i modellen kalibreres til et referencetilfælde, hvor en treakslet Scania bus passerer et jordlegeme af siltet ler. Et parameterstudie udføres for at belyse hvilke parametre, der er essentielle for ændringer i det oplevede vibrationsniveau på første sal af en bygning, når en bus passerer et fartbump eller en brostensbelægning foran bygningen. Nødvendigheden af at modellere koblingen mellem de forskellige dele af modellen undersøges ved at dekoble de enkelte led af modellem og sammenligne resultaterne med den samlede model. En tilsvarende tredimensionel model af problemet opstilles for at undersøge begrænsningerne i at anvende en todimensionel model.

Traffic-induced vibration in an urban environment can be an issue for neighbouring buildings and residents. Modifications in the pavement or construction of speed bumps may induce inconvenient vibration and in rare cases cause damage in buildings. Today’s methods, used for estimation of vibration from traffic, are mainly based on empirical knowledge and are relatively insecure. In the literature several examples can be found in which traffic-induced vibration and the response in nearby buildings are modelled numerically. However, no distinct consensus appears in the way the models are constructed, and the uncertainties are generally significant. The following master thesis with the title Numerical Analysis of Traffic-Induced Vibration deals with the construction of a dynamic finite-element model for simulation of traffic-induced vibration. The model includes a vehicle, a road, a soil body and a building. A plain two-dimensional finite-element model of a soil body with absorbing boundary conditions is constructed and a two-storey building is attached. A generic vehicle model is developed in which the wheels and the suspension system are modelled as discrete spring-dashpot-mass systems. Two types of surfaces are considered for the road: a plane surface with different types of speed bumps and a cobblestone pavement defined by stochastic parameters. The interface between the vehicle and the soil body is modelled using Mindlin beam elements supported by interface elements and Kelvin foundations. A key issue in the project is to examine the interaction effects between vehicle and soil body and between soil body and building. The interaction between vehicle and soil body is modelled in the time domain using three different time integration schemes: A decoupled, an explicit and an implicit scheme. The interaction between soil body and building is modelled by including the finite-element model of the soil body and the building in the same system. The parameters included in the model are calibrated for a reference case in which a three-axel vehicle similar to a Scania City bus runs across a soil of silty clay. A parameter study is conducted in order to clarify, which parameters are essential for the magnitude of the vibration in the building. Studies are performed for both speed bumps and cobblestone pavements. The necessity of coupling between the individual sub parts of the model is examined by conducting simulations for both a coupled and a decoupled model. Ultimately a three-dimensional model is developed for comparison in order to investigate whether a two-dimensional model is applicable for simulation of the threedimensional vibration problem.

A master thesis from Aalborg University

Numerical Analysis of Traffic-Induced Vibration

[Numerisk analyse af trafikinduceret vibrationer]