Glass Suspension Footbridge: Human-Induced Vibration, Serviceability Evaluation, and Vibration Mitigation

Abstract

Glass suspension footbridges or glass-bottomed suspension footbridges, such as the Zhangjiajie Grand Canyon Glass Bridge in China, are increasingly constructed in scenic regions as tourist attractions due to the glass-bottomed and transparent characteristics. Being installed in the second phase as a constant load, the glass deck is not designed to participate in the load bearing of the whole structure and thus the structure requires larger load-bearing capacity from other parts and a slightly different load-bearing system. More importantly, the glass deck weakens structural integrity and results in slightly smaller structural stiffness, which may result in globally lower natural frequencies. These structures may inevitably be more sensitive to the pedestrian-induced excitations. This paper investigates the human-induced vibrations of a typical glass suspension footbridge in China. The investigations are first performed based on intensive parametric studies. Except for the boundary conditions, the interlayers of glass, the vertical rise–span ratio and the axial stiffness of main cables, other governing parameters of the modal parameters for this type of structures are also identified, including the pavement load of the bridge deck system, the central buckle, and the prestress of wind-resistant cables. It may guide designers to take effective measures to improve the dynamic behavior of this type of structure. Next, the vibration serviceability assessments were performed based on different standards and guidelines such as the UK National Annex (NA) to Eurocode 1 (2008), the Bro2004 specification of Sweden, the HiVoSS guideline, and the ISO standard. Comparisons show that the UK NA to Eurocode 1, the HiVoSS guideline, and the ISO standard are more suitable for the vibration serviceability evaluations. These three codes consider the pedestrian-induced vibrations in both lateral and vertical directions and also consider both a small number of pedestrians and crowd-induced loads with different densities. Furthermore, comfort limits are not defined by only one limiting value but sorted into different levels. This may provide reference for the vibration serviceability evaluations of the other glass suspension footbridges. The assessments also show that changing the structural parameters can only partially reduce vibration levels and may result in different modal parameters to dominate the vibration responses. Thus, they recommend taking vibration mitigation measures to improve the vibration serviceability and suggest performing careful response calculations to ensure the effectiveness of vibration serviceability design if via changing the structural parameters. Finally, tuned mass dampers (TMDs) are installed to the structure. The results show that the popular TMD may effectively reduce the vibration levels.