A report by Portland State University (PSU) researchers offers an improved framework for assessing the seismic risk of transportation structures. Earthquake preparedness is a high priority for the Pacific Northwest, and cities and state agencies will benefit from having a more accurate and consistent way to prepare.

In collaboration with the Oregon Department of Transportation (ODOT) and the Federal Highway Administration (FHWA), the researchers developed a method to manage bridges and tunnels using various data sources and rigorous risk definitions. Traditionally, decisions about retrofitting existing structures have been based on expert opinion, past experience, or limited data, which can be subjective and incomplete for the estimation of seismic risk. This new research developed an automated method, underpinned by scientific understanding on seismic hazard and structural fragility, to make risk assessments more accurate, consistent, and helpful for choosing which retrofitting interventions should be a priority.

The research was sponsored by the FHWA Office of Bridges and Structures, and conducted by David Yang, Arash Khosravifar, and Diane Moug of PSU's Maseeh College of Engineering and Computer Science and Avinash Unnikrishnan at University of Alabama, Birmingham (former faculty at PSU) .

"Previously a lot of risk assessments were based on empirical assumptions or panel sessions where engineers sit together and try to evaluate what will be the hazard scenarios for our region, what are their frequencies, and what are the damage likelihood and extent to our transportation structures.. While this is useful, latest advances on earthquake engineering and  performance-based engineering can offer more reliable ways to assess risk," Yang said, “The challenge is how these latest advances can be incorporated into the asset management practice and bridge management systems (BMSs) used by transportation agencies. Our research aims to fill in this research gap.”

Existing BMSs use a table of expert-elicited hazard scenarios. Keeping the format of a risk table, the new method selects scenarios, evaluates likelihoods and consequences of scenarios, and weights their importance to overall risks, all based on well established information on hazard and structural characteristics from e.g., USGS and FEMA. This makes it more consistent and objective.

WHO CAN USE THIS RESEARCH?

Who are the stakeholders for accurate seismic risk assessment? It encompasses many: communities at risk, structural engineers, insurance and reinsurance industries, and various federal, state, and local agencies, such as the Federal Emergency Management Agency (FEMA), ODOT, Portland Bureau of Transportation (PBOT), and state and local emergency management offices.

The framework developed by the team accounts for direct monetary impacts due to both deterioration and natural disasters, as well as for indirect impacts on the functionality of highway networks. This lets various stakeholders identify which bridges, tunnels, or routes pose the greatest risk to the system performance — and make smarter, more cost-effective decisions to keep people and transportation networks safe.

The methods developed by the research team can handle large, complex networks and account for low-probability but high-impact events, and they outperform previous, more subjective approaches in both accuracy and robustness.

To facilitate application,  the model's source code is shared with FHWA and is accessible by agencies who wish to use it.

While this report focuses on earthquakes, the general theory can be adapted for other hazards as well, making it potentially useful for a wide variety of resilience efforts.

The report, "Framework and Methodology for Risk-Based Bridge and Tunnel Asset Management: Objective Risk Assessment and Network Level Evaluation," represents the first of a two-phase research project aimed at assessing and managing the condition and risk of bridges and tunnels. In the second phase, the research team will prepare a repository of risk tables for all the bridges in Oregon, creating a case study for the new method and helping ODOT to prioritize retrofits and repairs.

Portland State University's Transportation Research and Education Center (TREC) is a multidisciplinary hub for all things transportation. We are home to the Initiative for Bicycle and Pedestrian Innovation (IBPI), the data programs PORTAL and BikePed Portal, the Better Block PSU program, and PSU's membership in PacTrans, the Pacific Northwest Transportation Consortium. Our continuing goal is to produce impactful research and tools for transportation decision makers, expand the diversity and capacity of the workforce, and engage students and professionals through education, seminars, and participation in research. To get updates about what's happening at TREC, sign up for our monthly newsletter or follow us on social media. 

An Oregon Department of Transportation (ODOT) report, Resilient and Rapid Repair Measures for Seismically Vulnerable Bridges Following Major Earthquakes, introduces a rapid repair method for bridges in the event of a major earthquake.

The Cascadia Subduction Zone earthquake threatens bridges across the Pacific Northwest. Damage is expected to be geographically spread throughout the region and will have a nearly simultaneous impact on transportation through several important corridors. While bridge repair and replacement will ultimately be needed, an immediate priority will be resuming mobility. With that in mind, the project team developed a method for repairs to be implemented quickly.

The quick repair involves encasing a damaged bridge column in a steel jacket, which is then anchored to the foundation through replaceable ductile fuse hold-downs. In full-scale cyclic tests, the team applied this repair method to a damanged column and then subjected it to the cyclic loading it would encounter during a Cascadia Subduction Zone event. The experiments validated the design goal, resulting in restored or controlled strength while also exhibiting no additional damage.

The proof-of-concept experiments have shown the potential of this methodology to rapidly repair earthquake-damaged columns with a relatively generic approach.

Led by Peter Dusicka of Portland State University, the research team included AKM Golam Murtuz, Ilya Palnikov and Gregory Norton. Murtuz and Norton are currently graduate research assistants, Palnikov is a structural research engineer, and Dusicka is a professor and chair of civil and environmental engineering. All four team members work in the Maseeh College of Engineering & Computer Science at Portland State. Dusicka has worked on several other earthquake structural engineering projects, with a focus on infrastructure resilience.

Photo by Cait McCusker

The Transportation Research and Education Center (TREC) at Portland State University is home to the National Institute for Transportation and Communities (NITC), the Initiative for Bicycle and Pedestrian Innovation (IBPI), and other transportation programs. TREC produces research and tools for transportation decision makers, develops K-12 curriculum to expand the diversity and capacity of the workforce, and engages students and professionals through education.

David Yang, an assistant professor in the Department of Civil and Environmental Engineering at Portland State University, is the principal investigator on two newly-awarded research projects for the Federal Highway Administration (FHWA) in support of its structural engineering programs.

"As the transportation infrastructure continues to age in an ever more uncertain future, it is essential to assess and manage infrastructure risk during the evaluation, maintenance, and rehabilitation processes. These two projects are dedicated to the development of such risk-informed approaches for existing culverts, bridges, and tunnels," Yang said.

In the first project, Framework and Methodology for Risk-Based Bridge and Tunnel Asset Management, an infrastructure team led by Yang with co-PIs Diane Moug, Arash Khosravifar, and Avinash Unnikrishnan will use a three-year grant from the Federal Highway Administration to develop a framework and a methodology for asset management of bridges and tunnels.

Bridges and tunnels need to address the daily transportation needs of the traveling public and provide capacity and emergency service before/during/after extreme events. States may achieve the best possible transportation network performance through a properly planned asset management strategy. This project aims to develop a comprehensive and risk-based methodology that can consider all credible risks and their variations when maintenance and retrofitting actions are selected and implemented. This project will examine both regular operation, such as daily traffic fluctuation or planned maintenance/construction, and extreme events that have recurring intervals significantly greater than bridge design life span.

In the second project, Risk-Based Methodology for Structural Evaluation of Bridge-Sized Culverts, Yang and co-PIs Kevin White of E.L. Robinson Engineering of Ohio and Timothy Wood of The Citadel Military College of South Carolina will use another three-year FHWA grant to evaluate the structural integrity and assess risks for long-span culverts.

Many long-span culverts are subject to loads from heavy trucks, and thus need to be evaluated for their load carrying capacities to estimate safety margins. However, the current manual on bridge evaluation provides limited guidance for bridge-sized culverts due to their distinct structural configurations and different consequences of culvert overload. The project will develop a risk-based approach that can calibrate the varying target reliability levels of culverts and the associated load and resistance factors used for structural evaluation. By investigating all critical risk factors relevant to culvert safety under vehicle load, this research will formulate a risk-based methodology for evaluating bridge-sized culverts.

These two projects will support respectively the seismic and multi-hazard resilience program and the load rating program of FHWA, addressing its strategic goals and objectives in safety, infrastructure, innovation, and accountability.

The Transportation Research and Education Center (TREC) at Portland State University is home to the National Institute for Transportation and Communities (NITC), the Initiative for Bicycle and Pedestrian Innovation (IBPI), and other transportation programs. TREC produces research and tools for transportation decision makers, develops K-12 curriculum to expand the diversity and capacity of the workforce, and engages students and professionals through education.

Photo by Glen Richard/iStock