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| 2. |
- Bergenudd, Jens, et al.
(författare)
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Dynamic analysis of a pedestrian timber truss bridge at three construction stages
- 2024
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 59
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Tidskriftsartikel (refereegranskat)abstract
- This article investigates the dynamic behaviour of a single span pedestrian timber truss bridge by in situ testing and numerical modelling. The in situ dynamic tests were performed at three different construction stages: (1) on only the truss structure, (2) on the finished bridge without the asphalt layer and (3) on the finished bridge with the asphalt layer. The objective is to better understand how the different parts of the bridge contribute to the overall dynamic properties. The experimental results show that the damping ratios increased significantly for the first lateral mode (from 1.0 to 3.8%) and the first torsional mode (from 1.2 to 3.5%) between stage 2 and stage 3 due to the asphalt layer. The damping ratio is around 1.6% for the first bending mode for the finished bridge. The experimental and numerical results indicate that the stiffness of the asphalt layer is important to consider at stage 3 (10 degrees C) for the first lateral and torsional mode, but not for the first bending mode. Finally, it was concluded that longitudinal springs must be applied at the pot bearings in order to get agreement with the experimental results at all the three stages.
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| 3. |
- Bergenudd, Jens
(författare)
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Dynamic properties of two pedestrian timber bridges : Experimental and numerical analysis at several stages of construction
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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
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| 4. |
- Bergenudd, Jens, et al.
(författare)
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Dynamic testing and numerical modelling of a pedestrian timber bridge at different construction stages
- 2023
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Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 279
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Tidskriftsartikel (refereegranskat)abstract
- This article studies the dynamic properties of a single span pedestrian timber bridge by in-situ testing and numerical modelling. The in-situ dynamic tests are performed at four different construction stages: (1) on only the timber structure, (2) on the timber structure with the railings, (3) on the timber structure with railings and an asphalt layer during warm conditions and (4) same as stage 3 but during cold conditions. Finite element models for the four construction stages are thereafter implemented and calibrated against the experimental results. The purpose of the study is to better understand how the different parts of the bridge contribute to the overall dynamic properties. The finite element analysis at stage 1 shows that longitudinal springs must be introduced at the supports of the bridge to get accurate results. The experimental results at stage 2 show that the railings contributes to 10% of both the stiffness and mass of the bridge. A shell model of the railings is implemented and calibrated in order to fit with the experimental results. The resonance frequencies decrease with 10–20% at stage 3 compared to stage 2. At stage 3 it is sufficient to introduce the asphalt as an additional mass in the finite element model. For that, a shell layer with surface elements is the best approach. The resonance frequencies increase with 15–30% between warm (stage 3) and cold conditions (stage 4). The stiffness of the asphalt therefore needs to be considered at stage 4. The continuity of the asphalt layer could also increase the overall stiffness of the bridge. The damping ratios increase at all construction stages. They are around 2% at warm conditions and around 2.5% at cold conditions for the finished bridge.
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| 5. |
- Bergenudd, Jens, et al.
(författare)
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Study of the dynamic response of a timber pedestrian bridge during different construction stages
- 2022
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Ingår i: Conference Proceedings 4th ICTB (2022) ,ICTB 2021 PLUS 4th International Conference on Timber Bridges. - Biel/Bienne, Switzerland. ; , s. 167-178
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this article is to study the dynamic behaviour of a timber pedestrian bridge by performing in-situ tests at four different construction stages: 1) on only the timber structure 2) on the timber structure with the railings 3) on the timber structure with railings and an asphalt layer during warm conditions and 4) same as stage 3 but during cold conditions. The study included numerical calculations with a 2D finite element model. Two modal parameter extraction methods were implemented during the post-processing. The modes of vibration were analysed with the modal assurance criterion (MAC) to ensure their validity. The results show that the presence of the railings during stage 2 increases the resonance frequencies with 0-2 % compared to stage 1, despite an approximately 5 % increase of the total mass of the bridge. The vertical resonance frequencies decreased 12-22 % when the asphalt was installed at stage 3 compared to stage 2, due to an approximately 70 % increase of the total mass and the asphalt’s low stiffness due to a high temperature. The resonance frequencies increased 14-27 % during cold conditions at stage 4 compared to stage 3. This was mainly due to an increased stiffness of the asphalt layer due to a low temperature. Adding railings therefore resulted in a higher overall stiffness of the bridge, whereas asphalt essentially only added mass to the bridge at warm conditions but increased the stiffness at cold compared to warm conditions. The damping ratios increased for each construction stage and were approximately 2-3 % for the finished bridge. The two modal parameter extraction methods produced similar results which ensures that reliable results are obtained. The auto-MAC indicated well-separated modes and the cross-MAC ensured comparison of the same modes. The finite element model showed that some stiffness was lacking for the first bending mode. This stiffness could be due to shear deformation of the plastic pads at the bridge supports.
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