Louisiana State University, USA
Simulation of Vehicle-Bridge-Wind Interaction and its Applications
Problem
Bridges are an essential part of transportation infrastructures. Due to the progressive deteriorations and accumulated fatigue damages of structures under dynamic loads such as vehicles and wind, it is essential to ensure the structure safety in both routine service and extreme loading environments. For long-span bridges in extreme wind, no traffic load is typically considered, assuming that bridges will be closed to traffic at high wind speeds. Therefore, bridges are usually tested in wind tunnels or analyzed numerically without considering moving vehicles on them. On the other hand, when assessing bridge performance in routine service, such as fatigue damage, wind effects are not usually considered. However, there are numerous possible scenarios under which both vehicles and winds may simultaneously contribute to bridge responses and cause significant serviceability and bridge fatigue damage issues.
Approach
We develop a comprehensive framework for wind-vehicle-bridge interaction analysis. This includes both the experimental identification of the key parameters, and the development of numerical simulation tools to quantify the system performance. Along the way, we thus have developed a comprehensive approach to address vehicle and bridge safety issues, through the development of a three dimensional finite element analysis framework that considers the interaction of wind, bridge, and vehicles; the establishment of an experimental framework for both static and aerodynamic tests of bridge section models and vehicles. In the course of these developments, we conducted CFD prediction of wind loading on vehicles, evaluated the performance of vehicle safety and bridge fatigue in service, and bridge safety in extreme wind conditions. We also developed mitigation measures for bridge vibrations, studied vehicle dynamic impact on different bridges, and provided system identification based on vehicle-bridge interaction.
Recent Findings
The dynamic effects from vehicles are significant for short span bridges. When the road surface deteriorates or faulting forms at the bridge ends, bridge design codes may underestimate the dynamic impact factors and new specifications are needed for performance assessment of existing bridges. However, the vehicle dynamic impact effect is relatively small for long-span bridges and the effects from vehicle speeds and road roughness conditions can be neglected. Vehicle dynamic effects for FRP bridges can be significantly compared to traditional concrete and steel bridges. The combined dynamic effects from winds and vehicles might result in serious fatigue problems for long-span bridges, though the traffic or wind loads alone may not be able to induce serious fatigue problems.
Impact
This research provides a basis for improving bridge design codes. The developed relationship between safe driving vehicle speed and wind speed provides a starting point for developing a scientific traffic management strategy in windy environment, which can ultimately replace the current practice of closing a bridge or highway due to strong wind based on experience only. Finally, the strategy of using vehicle-bridge interaction to identify bridge or vehicle parameters will provide a new direction for bridge damage detection or vehicle law enforcement.
Selected Publications
1． Yin, X.F, Fang, Z., and Cai, C.S. (2011) ”Lateral Vibration of High-Pier Bridges under Moving Vehicular Loads” Journal of Bridge Engineering, ASCE, 16(3), 400-412.
2． Deng, Lu and Cai, C. S. (2009) “Identification of Parameters of Vehicles Moving on Bridges” Engineering Structures, 31(10), 2474-2485.
3． Zhang, Y., Cai, C. S., Shi, X. M. and Wang, C. (2006) “Vehicle induced dynamic performance of a FRP versus concrete slab bridge” J. of Bridge Engineering, ASCE, 11(4), 410-419.
4． Cai, C. S. and Chen, S. R. (2004) "Framework of vehicle-bridge-wind dynamic analysis."Journal of Wind Engineering and Industrial Aerodynamics, 92 (7-8), 579-607.