Evaluation of Visual Comfort on Long-Span Suspension Bridges Experiencing Vortex-Induced Vibrations: Basic Framework and a Case Study

Vortex-induced vibration is a prevalent form of wind-induced vibration during the operation period of long-span suspension bridges. It significantly influences the comfort of drivers and passengers and reduces the bridge's service capacity. Currently, the primary method for evaluating comfort relies on vibration acceleration standards, which lack a basis for assessing visual comfort. This paper presents a practical framework for the evaluation of visual comfort on long-span suspension bridges experiencing vertical vortex-induced vibration. A visual simulator is developed for drivers and passengers, taking the specific bridge modal shapes, vibration amplitudes, and vehicle speeds into consideration. By simulating the dynamic visual effects experienced by drivers and passengers on past vehicles, the comfort levels are investigated through a questionnaire based on visual comfort. An evaluation model is established for the drivers' subjective comfort response during vortex-induced vibration. The applicability and rationality of this evaluation process are illustrated through a typical case study. The results of the case study demonstrate that the comfort level of drivers and passengers is negatively correlated with the modal shapes and amplitudes under vortex-induced vibration conditions. Consequently, based on the visual comfort evaluation model, it is suggested that the maximum limit value for vertical vortex-induced vibration of the case study is 0.2-0.3 m. The proposed visual comfort evaluation process offers a comprehensive approach applicable to bridge serviceability.