Center for Transportation Research and Education

Bridge Engineering Center (BEC) researchers recently wrapped up two projects sponsored by the Federal Highway Administration (FHWA) to support its Office of Infrastructure (HIF) program.

The Guide for Orthotropic Steel Deck (OSD) Level 1 Design and Advancing Bridge Load Rating: State of Practice and Frameworks both concluded in December and are part of the Infrastructure Research and Technology Deployment Program.

Though the projects do not set national standards for their respective topics, they both aim to further standardize and simplify the processes in their respective areas.

“OSDs are durable, redundant, and lightweight, making them a popular option for both new design and the rehabilitation of signature structures. However, the complexity of design, sophisticated analysis requirements, large fabrication costs, and the possibility of owner-mandated experimental testing generally makes OSDs prohibitive for use with commonplace bridges,” said BEC Acting Director Justin Dahlberg, who served as principal investigator (PI) on the OSD guide project.

Dahlberg added that the intention of the guide is to further develop details of Level 1 design—using proven OSD solutions without the need for analysis—and to encourage the implementation of OSD systems.

Similarly, the bridge load rating project helps address the need for improved processes and consistency in standards via the identification and development of state of practice and future frameworks.

“Due to the vast bridge inventory in the US, establishing an efficient framework for the load rating, posting, and overweight permitting of bridges may be of great benefit to state agencies by providing consistency and by helping to optimize technological advancement capabilities,” said Bridge Research Engineer Brent Phares, who served as PI on the bridge load rating project.

Phares added that the technological advancements should improve the efficiency of decision-making while taking advantage of better load rating tools, which could also improve management of rehabilitation and replacement budgets.

More details about the respective projects are given in the following sections.

OSD Design Guide

The OSD design guide provides typical details similar to those for other bridge deck types. It includes design options for open-rib and closed-rib systems. Throughout the document, short summaries on the performance of several in-service OSD bridges are provided. Key points are also provided to highlight some of the benefits and drawbacks of one system over the other.

“Through the development of Level 1 design with typical details, the use of OSDs may become more common and fabrication costs may decrease as fabricators work with a small number of designs to establish economically viable fabrication processes,” said Dahlberg.

He noted that there are some negative perceptions of the OSD deck type given their complexity and cost as well as other factors, but the guide aims to provide clarity and note new technologies and methods that expedite rib fabrication and reduce costs.

The guide also notes that OSDs are highly redundant, which helps alleviate potential concerns that fatigue cracking or section corrosion loss will become an issue.

Additional details about the OSD guide are available at the project page.

Advancing Bridge Load Rating

The final report for the bridge load rating project addresses the future bridge rating needs through a review of the state of practice and the development of frameworks for next-generation bridge load rating, posting, and permitting.

Based on the extensive findings during the information collection processes for the project, the developed frameworks for future bridge load rating, posting, and overweight permitting aim to improve productivity, efficiency, and consistency by closing process gaps and through the application of newer technologies.

“Being able to load rate bridges efficiently and accurately is a necessity, particularly in the use case of permit load routing. In many instances, the permit office within different agencies evaluates non-standard loadings that potentially traverse complex structures to avoid negative impacts to commerce,” said Phares.

He added that the distributed load rating and posting processes across the nation are a significant effort that does and can benefit from improvements in efficiency, especially given that the US has more than 600,000 bridges. These processes have evolved individually in many states, but it is important that the states learn from one another and provide consistency.

Additional details about advancing bridge load rating are available at the project page.