Experimental and Numerical Dynamic Properties of Two Timber Footbridges Including Seasonal Effects

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.

Numerical modelling and vibration serviceability assessment of a steel footbridge with a significant 3D dynamic behaviour

“…Pfeil et al 25 propose a biodynamic model based on the single-degree-of-freedom (SDOF) system subjected to base excitation. In line with the variability of the structural parameters and the need to characterise the dynamic behaviour of the structure realistically, effort is currently being devoted to the investigation of temperature effects on the footbridges modal parameters, 26 and on how to discern those from damagerelated variations. 27 In the present work the dynamic response of an existing steel truss footbridge is evaluated after detecting relevant vertical and lateral vibrations on its main span.…”