Human-induced vibration assessment of a steel arch footbridge with tapered truss cross-section

Abstract The serviceability of pedestrian bridges may be affected by the discomfort due to vibrations felt by the users crossing the deck. Design guidelines recommend avoiding critical frequency ranges and provide acceptance criteria for maximum accelerations to assess user discomfort for serviceability conditions. The paper presents selected results from an experimental campaign on a two-hinged steel arch pedestrian bridge, analysing its dynamic response to both ambient and human-induced vibrations. Activities such as walking, running, and jumping are investigated. In this field, many research works are available in the scientific literature, but the vibration analysis of a steel arch footbridge with tapered truss cross-section is still missing. The first six vibration modes of the bridge are identified using the Frequency Domain Decomposition technique, while damping ratios are estimated through Enhanced Frequency Domain Decomposition. Walking and running tests reveal a small shift in the bridge's forced response frequencies compared to its free response. Jumping tests are analysed by isolating specific modal responses and estimating modal damping ratios based on free vibration data after the jump. The study also compares the maximum vertical accelerations recorded during these tests with the acceptance limits provided by technical standards. Overall, the paper provides insight into the vibration assessment of a steel arch footbridge with tapered truss cross-section and offers practical indications for field-data interpretation, as well as reference values of natural frequencies, damping ratios and accelerations for this common kind of infrastructures.