Dynamics of pedestrian timber bridges
Experimental and numerical analyses at various stages of construction
Time: Mon 2025-12-15 12.30
Location: Kollegiesalen, Brinellvägen 8, Stockholm
Video link: https://kth-se.zoom.us/j/64248423433
Language: English
Subject area: Civil and Architectural Engineering, Structural Engineering and Bridges
Doctoral student: Jens Bergenudd , Bro- och stålbyggnad
Opponent: Professor Peter Van den Broeck, KU Leuven
Supervisor: Professor Jean-Marc Battini, Bro- och stålbyggnad; Adjunct professor Roberto Crocetti, Byggnadsmaterial
QC 20251121
Abstract
Construction of pedestrian timber bridges is an important step towards creating a more sustainable future. However, bridges with resonance frequencies close to the pedestrian pacing frequencies can be susceptible to uncomfortable vibrations. Previous research work has shown that numerical models often require specific adjustments to agree with experimental results. The purpose of the present research project has therefore been to perform experimental and numerical dynamic analyses of five pedestrian timber bridges at different construction stages to increase the general knowledge regarding the implementation of more accurate finite element models.
The results showed that calibration of the longitudinal stiffness at the supports were required for the girder and truss bridges in Papers I-II. The connection stiffnesses between the timber members were required to calibrate the truss and arch bridges in Papers III-IV. The stiffness of the pile foundations was implemented in Paper III to calibrate the first bending mode. A simplified model of the pile foundations by modelling the soil with springs provided adequate results compared to a detailed model with solid elements. The partial composite action of the mechanically connected arch segments and vertical web members was quantified from laboratory experiments and was subsequently implemented in the numerical model of the finished arch bridge in Paper IV, which reduced the stiffness of the first lateral and torsional modes. The reduced axial stiffness of the stays due to their deformed catenary shape was implemented to fine-tune the first bending mode for the cable-stayed bridge in Paper V. The asphalt could generally be modelled as a mass at warm temperatures, but consideration of the asphalt stiffness was required at cold temperatures. Certain structural aspects such as the asphalt continuity at bridge ends and continuity between individual cross-laminated timber elements were also introduced. Railings with in-plane stiffness affected the mass and stiffness of the bridges equally much. The damping ratios typically increased with an asphalt layer on the bridge, especially for modes of vibration with large deformation of the asphalt. These damping ratios were in many cases considerably higher than the values from technical guidelines.
Several model uncertainties were identified and discussed such as the variability in material properties and stiffness definitions as well as climate variations between the construction stages. However, the aforementioned main factors that affected the dynamic properties of each bridge were established. The main conclusion is that most bridges required detailed consideration of certain structural aspects to achieve calibrated results.