Researchers Predict the Impact of Climate Change on Bridge Safety

A known fact is that climate change will eventually affect bridges. However, a lesser known fact is the extent to which bridges may be affected. This key question is addressed by scientists David Yang and Dan M. Frangopol in a study recently reported in ASCE Journal of Bridge Engineering.

We know climate change will increase the frequency and intensity of natural hazards like hurricanes, heat waves, wildfires, and extreme rains. For this paper, we’re looking at increased temperature as well as increased precipitation and their impact on bridge safety. The challenge here was that we didn’t know how to quantify those impacts to predict scour risk.

David Yang, Postdoctoral Research Associate, Civil and Environmental Engineering, Lehigh University

In the United States, scour is the main source of bridge failure. It occurs when floodwaters wash away the materials on all sides of the foundation of a bridge, forming scour holes that weaken the structural integrity.

In the study, Yang and Frangopol, a professor of civil engineering and the Fazlur R. Khan Endowed Chair of Structural Engineering and Architecture, had to fill the gap between the structural safety quantification and the climate data.

This was accomplished using hydrologic modeling that transforms climate simulation data into flow discharge data in the Lehigh River. The Lehigh River, a 109-mile-long tributary of the Delaware River, flows through the city of Bethlehem, Pennsylvania, where Lehigh University is situated.

We took a holistic approach. It started with a global climate model that was downscaled to regional hydrology, then we used structural engineering to get the failure probability of a structure in a future flooding event. From that, we could assess, does this structure failure pose certain risks to a community? So our model included these four steps of climatology, hydrology, structural engineering, and risk assessment.

David Yang, Postdoctoral Research Associate, Civil and Environmental Engineering, Lehigh University

He said this was the first study so far that has grouped all four steps to quantitatively analyze the effect of climate change on bridges. They developed their model by taking into account various climate futures and global climate models offered by the Intergovernmental Panel on Climate Change.

For evaluating the foundation depth of older bridges spanning the Lehigh River—data that is usually unavailable—they designed a method that can back-calculate the depth according to the condition ratings from the National Bridge Inventory. In addition, they took a regional and life-cycle approach to their study.

Frangopol is internationally famous for his groundbreaking work in life-cycle engineering, in which computational analysis is used to find the long-term value and hazards associated with infrastructure investments. In 2019, he was awarded the George W. Housner Structural Control and Monitoring Medal, one of many awards and honors presented to him by many professional organizations, in honor of his innovative work and leadership in the field.

Frangopol, as part of a research team including his former and current PhD students, will in fact receive the 2019 State of the Art of Civil Engineering Award during the forthcoming annual convention of the American Society of Civil Engineers (October 10–13^th, 2019) in recognition of their article, “Bridge Adaptation and Management under Climate Change Uncertainties: A Review.” He will receive this esteemed award for the third time.

According to Yang, choosing such a regional and life-cycle approach was a breakthrough for this study. “Bridges have a lot of microenvironments, and if you only look at one bridge, it’s really hard to capture the trend and get the increased risk from climate change,” he stated. “So we broadened this analytical horizon both spatially and temporally to capture long-term trends.”

Yang and Frangopol’s model resulted in eight conclusions. Of which, the most surprising was the degree to which the frequency of flooding might change.

“We realized that a 20-year flood may now become a 13-year flood at the end of the century, so that frequency nearly doubled,” stated Yang. “This is why climate change may induce an increased risk to infrastructure.”

Probably their most significant conclusion comprises the question of mitigation—in particular, what engineering measures should be employed to reduce hazard, and in which bridges.

“The reality is that budgets are limited,” remarked Frangopol, who is also associated with Lehigh’s Institute for Data, Intelligent Systems, and Computation (I-DISC) and the Institute for Cyber Physical Infrastructure and Energy (I-CPIE).

So it’s important to be able to determine, what is the priority here? You need to know the location of the bridge. For some communities, the failure of a bridge could be disastrous. For others, a bridge may not be as critical.

Dan M. Frangopol, Professor of Civil Engineering, Fazlur R. Khan Endowed Chair of Structural Engineering and Architecture, Lehigh University

Frangopol continued, “This model helps you make that kind of decisions because risk is not only based on safety but also on the consequences of failure. You might have two bridges at the same probability of failure, but the consequences of that failure could be very different.”

Although a focus on bridges along the Lehigh River was a clear choice due to their location, Yang and Frangopol were eager to share their model not only locally but also with all communities seeking to assess their infrastructure.

“We were inspired to do this research in part because historically Bethlehem was hit by multiple floods since 1902, and they had a significant impact on the community, so flooding is a significant hazard throughout the Lehigh River watershed,” stated Yang. “We wanted to devise something that the community can use to become adaptive to future climate change,” stated Frangopol.

The study was supported by the US National Science Foundation Grant CMMI 1537926 “Life-Cycle Management of Civil Infrastructure Considering Risk and Sustainability,” (2015–2020) with Dr Dan Frangopol as the only principal investigator.

Source: https://www1.lehigh.edu/