Truck platooning happens when two or more semi-trailer trucks travel closely together in a convoy and is often utilized to save fuel, improve the environment, and improve traffic operations. While this strategy is effective in those areas, it can also potentially overload structures such as girder bridges. In his project “Truck Platooning Effects on Girder Bridges: Phase II – Service”, Dr. Joshua Steelman investigates this concept.
Dr. Steelman is an associate professor and Complete Engineer Fellow in the Department of Civil and Environmental Engineering at UNL. He is also a researcher and has been Principal Investigator on projects at UNL’s Midwest Roadside Safety Facility. His areas of research include roadside safety, bridging, and structures design and performance evaluation. He was joined in this project by faculty Dr. Jay Puckett, Dr. Daniel Linzell, and Doctorate student Bowen Yang.
His previous reliability-based studies have focused on the Strength I limit state and have shown that trucks may operate at weights exceeding standard legal load limits for bridges, even when their headways (distance between vehicles measured in space or time) meet the regulation. A Strength I limit state is a bridge’s operation under normal use of traffic, people, and environment (not including wind).
The AASHTO Manual for Bridge Evaluation does not currently have a target implicit reliability index, which indicates the reliability of code-compliant bridge designs. It also does not have a reliability-based evaluation guidance for the four service limit states, which are specific load combinations relating to stress, deformation and cracking and is met when the bridge can no longer function. There is also a gap in service limit state evaluation protocols for bridges subjected to platoons. This study aimed to address these gaps by considering girder spacings, span lengths, span numbers, structure types, truck configurations, truck numbers, and adjacent-lane loading scenarios in a Monte Carlo Simulation model to identify target reliability index values based on current design loads.
They began research by identifying three primary platooning scenarios and choosing four bridge types. Reliability analyses were performed for the platoon and bridge scenarios with a Service III limit state (when cracks are formed by tension in prestressed concrete superstructures and segmental concrete girders webs) and Service II limit state (applicable to steel bridges, when there are permanent deformations due to localized yielding or a slip of connections).
From these results, target implicit reliability index values were given for Service III and Service II platoon load ratings they could then use with examples of the four bridge types in Nebraska. The conclusion produced a headway guidance for service limit states that would illustrate potential safe operational strategies for varying truck weights and platoon uncertainties.
This project was funded by the Nebraska Department of Transportation and USDOT Federal Highway Administration and the report will soon be available for public viewing and download.