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

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

Numerical and experimental dynamic analyses of the Vega Pedestrian bridge including seasonal effects

As timber structures become increasingly relevant and sought after – since they enable improvements in building time while reducing a structure’s life cycle impacts – streamlining their design can have meaningful economic and environmental implications.For timber footbridges, its design is frequently governed by serviceability criteria linked to excessive vibrations. To address this in design, it is necessary to correctly characterize the structure’s dynamic properties and understand what the leading parameters in its behaviour are.This thesis studied an existing timber arch footbridge, aiming to evaluate its dynamic behaviour both with experimental measurements and with theoretical models. The influence of temperature change over different seasons was considered, particularly around its effect on the asphalt layer – whose stiffness is highly correlated to temperature.The experimental results showed high correlation between temperature and natural frequencies: a variation of +21°C reduced the natural frequency for the 1st transverse mode of the deck by as much as 30.6% while the 1st vertical mode was reduced by 17.7% (variation of 0.029Hz/°C).The damping ratio was also measured, though a definitive correlation between its value and temperature was not identified.This change in behaviour cannot be explained by the influence of the asphalt layer alone however, as there is a high degree of uncertainty around many other components of the bridge and their interactions, such as the connections.Thus, to fully characterize the influence of each component with changing temperature, further experimental tests would have to be performed, or simpler structures with fewer connections should be considered.In designing a new structure, considering the asphalt layer as an added mass is a straightforward way to treat this material at the most critical condition (i.e. no contribution to stiffness). This strategy lead to sufficiently similar results between the computational model and the experimental results at warm temperatures.The asphalt stiffness could perhaps be considered for the 1st transverse mode of the deck, since it is in this mode that the asphalt layer plays its largest contribution

Numerical and experimental dynamic analyses of the Vega Pedestrian bridge including seasonal effects

As timber structures become increasingly relevant and sought after – since they enable improvements in building time while reducing a structure’s life cycle impacts – streamlining their design can have meaningful economic and environmental implications.For timber footbridges, its design is frequently governed by serviceability criteria linked to excessive vibrations. To address this in design, it is necessary to correctly characterize the structure’s dynamic properties and understand what the leading parameters in its behaviour are.This thesis studied an existing timber arch footbridge, aiming to evaluate its dynamic behaviour both with experimental measurements and with theoretical models. The influence of temperature change over different seasons was considered, particularly around its effect on the asphalt layer – whose stiffness is highly correlated to temperature.The experimental results showed high correlation between temperature and natural frequencies: a variation of +21°C reduced the natural frequency for the 1st transverse mode of the deck by as much as 30.6% while the 1st vertical mode was reduced by 17.7% (variation of 0.029Hz/°C).The damping ratio was also measured, though a definitive correlation between its value and temperature was not identified.This change in behaviour cannot be explained by the influence of the asphalt layer alone however, as there is a high degree of uncertainty around many other components of the bridge and their interactions, such as the connections.Thus, to fully characterize the influence of each component with changing temperature, further experimental tests would have to be performed, or simpler structures with fewer connections should be considered.In designing a new structure, considering the asphalt layer as an added mass is a straightforward way to treat this material at the most critical condition (i.e. no contribution to stiffness). This strategy lead to sufficiently similar results between the computational model and the experimental results at warm temperatures.The asphalt stiffness could perhaps be considered for the 1st transverse mode of the deck, since it is in this mode that the asphalt layer plays its largest contribution

Numerical and experimental dynamic analyses of the Vega Pedestrian bridge including seasonal effects

As timber structures become increasingly relevant and sought after – since they enable improvements in building time while reducing a structure’s life cycle impacts – streamlining their design can have meaningful economic and environmental implications.For timber footbridges, its design is frequently governed by serviceability criteria linked to excessive vibrations. To address this in design, it is necessary to correctly characterize the structure’s dynamic properties and understand what the leading parameters in its behaviour are.This thesis studied an existing timber arch footbridge, aiming to evaluate its dynamic behaviour both with experimental measurements and with theoretical models. The influence of temperature change over different seasons was considered, particularly around its effect on the asphalt layer – whose stiffness is highly correlated to temperature.The experimental results showed high correlation between temperature and natural frequencies: a variation of +21°C reduced the natural frequency for the 1st transverse mode of the deck by as much as 30.6% while the 1st vertical mode was reduced by 17.7% (variation of 0.029Hz/°C).The damping ratio was also measured, though a definitive correlation between its value and temperature was not identified.This change in behaviour cannot be explained by the influence of the asphalt layer alone however, as there is a high degree of uncertainty around many other components of the bridge and their interactions, such as the connections.Thus, to fully characterize the influence of each component with changing temperature, further experimental tests would have to be performed, or simpler structures with fewer connections should be considered.In designing a new structure, considering the asphalt layer as an added mass is a straightforward way to treat this material at the most critical condition (i.e. no contribution to stiffness). This strategy lead to sufficiently similar results between the computational model and the experimental results at warm temperatures.The asphalt stiffness could perhaps be considered for the 1st transverse mode of the deck, since it is in this mode that the asphalt layer plays its largest contribution

Numerical and experimental dynamic analyses of the Vega Pedestrian bridge including seasonal effects

As timber structures become increasingly relevant and sought after – since they enable improvements in building time while reducing a structure’s life cycle impacts – streamlining their design can have meaningful economic and environmental implications. For timber footbridges, its design is frequently governed by serviceability criteria linked to excessive vibrations. To address this in design, it is necessary to correctly characterize the structure’s dynamic properties and understand what the leading parameters in its behaviour are. This thesis studied an existing timber arch footbridge, aiming to evaluate its dynamic behaviour both with experimental measurements and with theoretical models. The influence of temperature change over different seasons was considered, particularly around its effect on the asphalt layer – whose stiffness is highly correlated to temperature. The experimental results showed high correlation between temperature and natural frequencies: a variation of +21°C reduced the natural frequency for the 1st transverse mode of the deck by as much as 30.6% while the 1st vertical mode was reduced by 17.7% (variation of 0.029Hz/°C). The damping ratio was also measured, though a definitive correlation between its value and temperature was not identified. This change in behaviour cannot be explained by the influence of the asphalt layer alone however, as there is a high degree of uncertainty around many other components of the bridge and their interactions, such as the connections. Thus, to fully characterize the influence of each component with changing temperature, further experimental tests would have to be performed, or simpler structures with fewer connections should be considered. In designing a new structure, considering the asphalt layer as an added mass is a straightforward way to treat this material at the most critical condition (i.e. no contribution to stiffness). This strategy lead to sufficiently similar results between the computational model and the experimental results at warm temperatures. The asphalt stiffness could perhaps be considered for the 1st transverse mode of the deck, since it is in this mode that the asphalt layer plays its largest contribution

Numerical and experimental dynamic analyses of the Vega Pedestrian bridge including seasonal effects

As timber structures become increasingly relevant and sought after – since they enable improvements in building time while reducing a structure’s life cycle impacts – streamlining their design can have meaningful economic and environmental implications. For timber footbridges, its design is frequently governed by serviceability criteria linked to excessive vibrations. To address this in design, it is necessary to correctly characterize the structure’s dynamic properties and understand what the leading parameters in its behaviour are. This thesis studied an existing timber arch footbridge, aiming to evaluate its dynamic behaviour both with experimental measurements and with theoretical models. The influence of temperature change over different seasons was considered, particularly around its effect on the asphalt layer – whose stiffness is highly correlated to temperature. The experimental results showed high correlation between temperature and natural frequencies: a variation of +21°C reduced the natural frequency for the 1st transverse mode of the deck by as much as 30.6% while the 1st vertical mode was reduced by 17.7% (variation of 0.029Hz/°C). The damping ratio was also measured, though a definitive correlation between its value and temperature was not identified. This change in behaviour cannot be explained by the influence of the asphalt layer alone however, as there is a high degree of uncertainty around many other components of the bridge and their interactions, such as the connections. Thus, to fully characterize the influence of each component with changing temperature, further experimental tests would have to be performed, or simpler structures with fewer connections should be considered. In designing a new structure, considering the asphalt layer as an added mass is a straightforward way to treat this material at the most critical condition (i.e. no contribution to stiffness). This strategy lead to sufficiently similar results between the computational model and the experimental results at warm temperatures. The asphalt stiffness could perhaps be considered for the 1st transverse mode of the deck, since it is in this mode that the asphalt layer plays its largest contribution