Abstract
This paper deals with experimental and numerical dynamic analyses of two timber footbridges. Both bridges have a span of 35 m and consist of a timber deck supported by two timber arches. The main purpose is to investigate if the dynamic properties of the bridges are season dependent. To this end, experimental tests are performed during a cold day in winter and a warm day in spring in Sweden. The first bending and transverse mode frequencies increase 22% and 44%, respectively, due to temperature effects in the case of Vega Bridge. In the case of Hägernäs bridge, the corresponding values are 5% and 26%. For both bridges, the measured damping coefficients are similar in winter and spring. However, the damping coefficients for the first bending and transverse modes are different for both footbridges: about 1% for the Hägernäs bridge and 3% for the Vega bridge. Finite-element models are also implemented. Both numerical and experimental results show good correspondence. From the analyses performed, it is concluded that the connections between the different components of the bridges have a significant influence on the dynamic properties. In addition, the variation of the stiffness for the asphalt layer can explain the differences found in the natural frequencies between spring and winter. However, due to the uncertainties in the modelling of the asphalt layer, this conclusion must be taken with caution.
Highlights
In addition to its ecological benefits, wood presents several advantages as construction material for pedestrian bridges: it provides a high-bearing capacity relative to the self-weight; it has the ability, by incorporating steel details, of satisfying the nowadays increasing aesthetic demand; it allows for an industrial manufacturing process in which large parts of the structure are produced and transported to site for easy erection and assembling, etc
The experimental and dynamic performances of timber bridges have been the purpose of several research works in the last decade [2,3,4,5], including structural health monitoring analyses [6], evaluation of natural frequencies variations with the time and use [7], etc
The purpose of this paper is to study, both experimental and numerically, the dynamic properties of two existing pedestrian wooden bridges. Both bridges present a span length of approximately 35 m and consist of a timber deck supported by two timber arches
Summary
In addition to its ecological benefits, wood presents several advantages as construction material for pedestrian bridges: it provides a high-bearing capacity relative to the self-weight; it has the ability, by incorporating steel details, of satisfying the nowadays increasing aesthetic demand; it allows for an industrial manufacturing process in which large parts of the structure are produced and transported to site for easy erection and assembling, etc. The relatively low stiffness of timber bridges in combination with their low self-weight may result in uncomfortable vibrations for crossing pedestrians, and accurate dynamic analyses are often required in the design process. For this reason, the experimental and dynamic performances of timber bridges have been the purpose of several research works in the last decade [2,3,4,5], including structural health monitoring analyses [6], evaluation of natural frequencies variations with the time and use [7], etc. Several studies [8,9,10] have shown that predicting the stiffness of the connections in the design phase is very challenging and that it can only be done accurately after completion of the bridge by calibrating the model against experimental measurements
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