improvement of dynamic behavior of suspension footbridges by modification on hangers’ system arrangement

The hanger systems of the footbridges are used in two vertical and inclined forms. both systems have their advantages and disadvantages. the inclined hangers are more prone to slackness and fatigue phenomenon, and are stressed too much. there is no much slackness, fatigue phenomenon and overstress in the vertical system, but this system is more prone to vertical vibration at low frequencies than inclined ones. in recent years, a new modification has been made to eliminate deficiencies in the inclined hanger system. in the modified system, the slackness phenomenon has been removed completely and the force variations of two adjacent hangers have been reduced significantly. in this study, modeling and analysis of the footbridge were performed with csi bridge software and the disadvantages of the old modified hanger system are eliminated by proposing a new modified hanger system. a modal analysis was also carried out to compare the dynamic characteristic such as natural modes and frequencies on a footbridge with the vertical, inclined, old modified, and new modified hanger systems. results showed that the new modified hanger system was improved compared with the old one in the terms of vertical vibration mode so that the new system had no vertical frequency in the pedestrian vertical frequency range.