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Wind effects on simple girder bridges during construction stages
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
2019 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Wind is dynamic by nature, but its actions on structures were considered as static loads until thecollapse of Tacoma Narrows Bridge (1940). Nowadays, due to the developments in civil engineering,bridge designs are becoming slenderer and lighter, which makes wind dynamic eects even moreimportant than wind static eects. Furthermore, some types of bridges show specially vulnerablesituations during constructions stages, when the structure is lighter or does not have its nalstiness. The aim of this document is to assess the dynamic wind loading on simple girder bridgesduring their construction phases. Particularly, the studied section is formed by two steel beamssupporting a concrete slab. The analysis was made when the concrete slab has not been built yetand only the steel parts are in their positions. Eurocode 1 proposes some analytical methods toanalyse dynamic wind loads, but the parameters given are only for simple sections.Several CFD simulations were done with the software Ansys-Fluent to nd the aerodynamic parametersdepending on section's dimensions. The geometrical parameters tested were the heightof the beams (h), the distance between beams (d) and the height of the bridge (H). Three valueswere assigned to each parameter, and beams' width was set to b = 0:9m. Tree construction stageswere analysed. First, when only one beam is exposed to the wind, second, when the two beams arein their nal locations but they are not connected yet and, by last, when both beams are joinedby the bracing. Extra uid simulations were made with closed sections, in order to see if isolatingthe space between the beams with plates improves section's vulnerability. The results showed thatvortex shedding eects are stronger in the along-wind direction due to the low horizontal bendingstiness of the beams and their high area perpendicular to the ow. Increasing beams' distanceshowed to be a good solution to reduce wind eects. However, the alternative of closing the sectionwith light plates had the best results, decreasing the frequency of vortex shedding and its eects.Moreover, the obtained results were used to analyse the vulnerability of Banafjal Bridge with themethods proposed by Eurocode 1. The eects of vortex shedding on the bridge showed to be ofimportance only when just one beam is in its nal location. The low actions seemed to be becauseof the low frequencies of the bridge, which caused the resonance to occur with low wind speeds.Increasing bridge's natural frequencies the wind loads would increase, leading to high accelerationsthat could reduce the safety or the comfort of the workers. Anyway, the stresses were far fromsteel's elastic limit. Regarding bueting loads, with wind speeds above 25-30 m/s, or 40-45 m/swhen the bracing is done, the elastic limit of the steel was reached, leading to undesirable residualstresses in the beams. Increasing beams' width was in this case the best option to reduce buetingeects.

Place, publisher, year, edition, pages
2019.
Series
TRITA-ABE-MBT ; 19539
Keywords [en]
Vortex shedding, Bueting, Dynamic wind eects, Computational Fluid Dynamics, Parametric study, Simple girder bridge, Structure aerodynamics. i
National Category
Other Engineering and Technologies
Identifiers
URN: urn:nbn:se:kth:diva-254342OAI: oai:DiVA.org:kth-254342DiVA, id: diva2:1330970
Available from: 2019-06-26 Created: 2019-06-26 Last updated: 2019-10-04

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