Dynamic model updating including pedestrian loading applied to an arched timber footbridge

Abstract

This paper shows the experimental procedure and numerical methodology used for the dynamic characterization and serviceability assessment abilities (by simulation) applied to a timber pedestrian walkway. The footbridge is a 47 meters long and 3.9 meters wide structure consisting on single wooden arch (3.4 m sag), wooden deck, steel hangers and steel cross-bracings, designed by Media Madera Ingenieros Consultores. With applied research aims, an experimental campaign was carried out in April 2018. Useful data was collected to calibrate the corresponding computational structural and loading models. After that, a serviceability dynamic simulation can be carried out to quantify the vibrations induced by a pedestrian when crossing the bridge. Although there may be some other works with similar objectives and methodology, the peculiarity of this structure is that its first mode shapes are the antisymmetric ones and that it has two close modes within the excitable range by human locomotion activities. The modes were obtained experimentally after a modal analysis by arranging 10 accelerometers on the deck. With the experimental information and the corresponding geometry, the modeling using the finite elements method, together with its updating, is followed. A close match in terms of frequency response functions and mode shapes is achieved. Once the mechanical model is updated, some adjusts must be done in the pedestrian loading model so that the computational dynamic response matches with the real one under a single walking pedestrian crossing at resonance. After all the adjustments done, the computational model is ready to estimate the response of the structure undergoing other pedestrian actions and its serviceability condition when other loading scenarios are applied.