Investigating the Impact Factor of Cable Stayed Bridges under the Passage of Moving Load at Different Speeds

Abstract

Due to developments in the field of fast transportation, increase in permitted speed and load capacity, moving loads can have significant effects on the dynamic forces of bridges. To consider the dynamic effect in the design of the structure, the dynamic impact factor is introduced as ratio of the dynamic response to the static response. Accurate evaluation of these coefficients helps in safe and economic designs for new bridges. However, the evaluation of the dynamic impact factor is difficult due to the vehicle-bridge interaction and the influence of many parameters that affect the dynamic impact factor, including the dynamic characteristics of the bridge and the vehicle, road surface conditions, vehicle speed, traffic conditions,. In this research, by applying live load of vehicles step by step and performing time history analysis, dynamic analysis under moving load has been done. Three different types of cable-stayed bridges with different spans and cable layouts have been investigated in the form of two-dimensional models. This study analyzes the impact coefficient of bending and shear forces of deck components and pylons, as well as the axial forces of cables, and the results are compared with the coefficients proposed in the design regulations. Also, the effect of changes in load passing speed on the dynamic impact factor in cable-stayed bridges has also been evaluated and studied. This research tries to improve and optimize the design and performance of cable-stayed bridges in order to deal with dynamic changes and increase the speed of loads.

Keywords

• cable-stayed bridges
• dynamic analysis of moving load
• impact factor (im)
• allowable dynamic load (dla)
• dynamic amplification factor (daf)