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

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 frst bending and transverse mode frequencies increase 22% and 44%, respectively, due to temperature efects 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 coefcients are similar in winter and spring. However, the damping coeffcients for the frst bending and transverse modes are diferent 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 diferent components of the bridges have a signifcant infuence on the dynamic properties. In addition, the variation of the stifness for the asphalt layer can explain the diferences 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.