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Dynamic properties of two pedestrian timber bridges

Experimental and numerical analysis at several stages of construction

Time: Mon 2023-04-03 13.00

Location: M108, Brinellvägen 23, Stockholm

Video link:

Language: English

Subject area: Civil and Architectural Engineering, Structural Engineering and Bridges

Doctoral student: Jens Bergenudd , Bro- och stålbyggnad

Opponent: Professor Patricia Hamm, Biberach University of Applied Sciences

Supervisor: Professor Jean-Marc Battini, Bro- och stålbyggnad; Adjunct Professor Roberto Crocetti, Byggnadsmaterial

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Pedestrian bridges can beneficially be made from timber in order for our society to reach a sustainable future. This positive development is partly made possible due to advances in engineered wood products (e.g. glued laminated timber) and the possibilities for pre-fabrication of structural parts. Timber bridges, especially long and slender, can however be susceptible to uncomfortable vibrations which could be solved by more accurate dynamic analysis in the design phase. Common issues reported by previous research are the difficulties in accurate predictions of the natural frequencies without calibration against experimental results. The purpose with the present research work is therefore to perform dynamic analysis of two pedestrian timber bridges at different construction stages in order to better understand the influence of different structural parts in the numerical models. The results show that the estimated and applied values for the densities of the timber (Norway spruce and Scots pine) are slightly higher than in the norm. Both bridges required calibration of longitudinal stiffness at the supports for the numerical results to agree with the experiments. The railings could be omitted from the numerical models for both bridges, which is in contrast with common engineering practise where they are often considered as an additional mass. The stiffness of the asphalt was required at low temperatures (10 °C and 0 °C). However, the asphalt could be modelled as an additional mass at a high temperature (40 °C) where special care also could be given to the effects of the composite cross-section geometry (timber deck and asphalt). The level of detail for the modelling of the truss joints, the connection truss/crossbeam and the connection deck/crossbeams proved to be an important issue for the Stela bridge. The damping ratios (ζ) increased with an asphalt layer on the bridge and are slightly higher than the values recommended by the norms. This may be relevant to consider in the design phase. However, it may be difficult to derive general conclusions for other pedestrian timber bridges since this thesis only concerns case studies of two bridges. More studies of other types of bridges are therefore necessary in order to confirm or disprove the present results