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Modal analysis of pedestrian-induced torsional vibrations based on validated FE models
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
2017 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Finite element (FE) models serve as the base of many different types of analysis as e.g. dynamic analysis. Hence, obtaining FE models that represent the actual behaviour of real structures with great accuracy is of great importance. However, more often than not, there are differences between FE models and the structures being modelled, which can depend on numerous factors. These factors can consist of uncertainties in material behaviour, geometrical properties and boundary- and continuity conditions. Model validation is therefore an important aspect in obtaining FE models that represents reality to some degree. Furthermore, model verification is also important in terms of verifying theoretical models, other than FE models, in fields such as fatigue-, fracture- and dynamic analysis.

In this thesis, two pedestrian steel bridges, the Kallhäll bridge and the Smista bridge, have been modelled in a FE software based on engineering drawings and validated against experimental results with regard to their natural frequencies. Furthermore, in this thesis, a model has been developed in MATLAB based on modal analysis that accounts for pedestrian-induced torsional vibrations, the 3D SDOF model. This model has been verified against the previously mentioned FE models.

The aim of this thesis is hence two parted where the first part is to develop three-dimensional FE models of two pedestrian bridges and validate them against measured data regarding the natural frequencies. The second part is to further develop a model for analysing the effect of pedestrian-induced torsional vibrations and to investigate whether the model captures the actual dynamic response of such loading.

The results showed that the natural frequencies for the first bending- and torsional mode from the FE models corresponded well to the measured ones with the largest difference of 5 \% obtained for the natural frequency of the first bending mode for the Smista bridge. Furthermore, the 3D SDOF model was able to capture the dynamic response of torsional vibrations with an overall difference of less than 2 \% in comparison to the FE models. The model can be improved by further studying the pedestrian-structure interaction as well as studying the effect of using approximative functions describing the mode shapes.

Abstract [sv]

Finita elementmodeller (FE-modeller) utgör en bas för många olika typer av analyser som exempelvis dynamiska analyser. Därmed är det av stor betydelse att FE-modeller representerar det faktiska beteendet av verkliga strukturer med stor noggrannhet. Ofta är det emellertid skillnader mellan FE-modeller och de verkliga strukturer man modellerar. Dessa skillnader kan bero på en rad faktorer såsom exempelvis osäkerheter i materialbeteende, geometriska egenskaper samt upplag- och randvillkor. Modellvalidering är därför en viktig aspekt i att erhålla FE-modeller som representerar verkligheten i olika omfattningar. Utöver modellvalidering är även modellverifiering viktigt, inte endast för verifiering av FE-modeller utan även för verifiering av andra teoretiska modeller inom områden såsom utmaning-, fraktur- och dynamiska analyser.

I detta arbete har två GC-broar, Kallhäll- och Smistabron modellerats i ett FE-program baserat på konstruktionsritningar och validerats mot experimentella resultat med avseende på de naturliga frekvenserna. Vidare har det i detta arbete utvecklats en modell i MATLAB som tar hänsyn till människo-inducerade torsionsvibrationer baserat på modalanalys, benämnd 3D SDOF modellen. Modellen har även verifierats mot de tidigare nämnda FE-modellerna.

Målet med detta arbete är således uppdelat i två delar, där den första delen består av att utveckla tredimensionella FE-modeller av två GC-broar samt validera dessa mot mätdata vad gäller de naturliga frekvenserna. Den andra delen består av att utveckla en modell för att analysera effekten av människo-inducerade torsionsvibrationer och undersöka huruvida modellen fångar den dynamiska responsen.

Resultaten visade att de naturliga frekvenserna för den första böj- och vridmoden från FE-modellerna motsvarade de uppmätta frekvenserna med en största relativ skillnad på 5 \% för den fösta böjmoden för Smistabron. Vidare visade resultaten att den utvecklade 3D SDOF modellen kunde fånga den dynamiska responsen av torsionsvibrationer med en skillnad på mindre än 2 \% i jämförelse med resultat från de FE-modellerna. Modellen kan förbättras genom att vidare studera interaktionen mellan fotgängare och gångbro samt studera effekten av att använda approximativa funktioner som beskriver modformen.

Place, publisher, year, edition, pages
2017. , p. 58
Series
TRITA-BKN-Examensarbete, ISSN 1103-4297 ; 509
Keywords [en]
Modal analysis, validated FE models, pedestrian-induced vibrations
National Category
Civil Engineering
Identifiers
URN: urn:nbn:se:kth:diva-209956OAI: oai:DiVA.org:kth-209956DiVA, id: diva2:1115702
External cooperation
Tyréns AB
Educational program
Master of Science in Engineering - Urban Management
Supervisors
Examiners
Available from: 2017-06-27 Created: 2017-06-27 Last updated: 2017-06-27Bibliographically approved

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