An Analysis of the Dynamic Response of Suspension Footbridges Measured Against Human Comfort Criteria

Open Access
Author:
Kearney, Jennifer A
Graduate Program:
Civil Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 01, 2015
Committee Members:
  • Jeffrey A Laman, Thesis Advisor
Keywords:
  • footbridges
  • serviceability
  • dynamic analysis
Abstract:
Many rural communities around the world become isolated from their basic needs during the rainy season, so pedestrian suspension bridges are being built to provide hundreds of thousands of people with basic access. However, suspension pedestrian bridges have low stiffness, mass, and damping, causing them to be prone to vibration problems. Pedestrian loading can cause a dynamic effect that creates public alarm to the point where bridge users perceive it to be unsafe. The present study analyzed two scaled, physical models and forty numerical models to determine how changing certain design parameters affects modal frequencies and the dynamic response compared to human comfort limits. The physical models were created to calibrate and validate the numerical models which were used to conduct the parametric study, which included a modal analysis and time-history analysis of a person walking across the bridge. The parametric study analyzed span length, cable sag, vertical stiffening, and lateral stiffening. The study determined that the modal frequencies of pedestrian suspension bridges do not meet the recommended ranges and the vertical velocities, lateral accelerations, and vertical accelerations of the structure when one pedestrian walks across exceed human comfort limits. Shorter span lengths have higher modal frequencies and dynamic responses. Lower cable sags have higher vertical frequencies and lower vertical dynamic responses. Adding stiffening increases the frequencies and decreases the dynamic response, but the response still exceeds human comfort limits.