Monday, August 15, 2016

Faculty Members Help ODOT Save Time and Money on Post-Earthquake Bridge Inspection

Earthquakes affecting Oklahoma in 2016. (Source: U.S. Geological Survey).
Over the last decade, Oklahoma has experienced an alarming increase in earthquake activity. We are now the earthquake capital of the United States, having registered 907 magnitude 3 or larger earthquakes in 2015 (Fig. 1)—more than California and Alaska. The increased activity has heightened the public’s awareness, as well as researchers’ interest.

In light of this increasing threat, the Oklahoma Department of Transportation hired a team to revise its post-earthquake response plan. The team is composed of industry partners and university researchers. Led by Gregg Hostetler of Infrastructure Engineers Inc., the team includes CEES assistant professor Scott Harvey and professor K.K. “Muralee” Muraleetharan. Harvey and Muraleetharan played a key role in updating the ODOT’s post-earthquake inspection protocol and analyzing three critical bridges to understand the structural vulnerabilities of these bridges during earthquakes. They were supported by two CEES students: graduate student Ivanna Kaid Bay Cortez and architectural engineering accelerated master’s student Samantha Heinrich.

ODOT’s previous protocol dictated that all bridges within a five-mile radius from the epicenter were to be inspected for all magnitude 4 and larger earthquakes. In 2015, inspection crews had to be mobilized a total of 31 times, placing a burden on the department’s resources and inspectors’ morale as no damage due to earthquakes was ever identified. To revise ODOT’s inspection radii, the OU researchers examined both the capacity of and seismic demand on ODOT bridges. Bridge capacity was measured using standard fragility curves, which give the probability of a bridge being in a certain state of damage based on the intensity of shaking, while the seismic demand on the bridges was characterized by the expected intensity of shaking. In order to predict intensity of shaking, Heinrich calibrated an existing ground-motion prediction equation for Oklahoma based on collected Oklahoma ground motions.

The results of the research indicated that ODOT’s previous protocol was overly conservative and led to a recommendation for ODOT to update their protocol. For example, the research showed that earthquakes of magnitude 4.6 or smaller are unlikely to cause damage to ODOT’s bridges. The research also led to reduction in inspection radii. The department officially enacted the proposed protocol when the results were publicly released on March 31, 2016. ODOT chief engineer Casey Shell said, “We were conservative in our approach to bridge inspections, but now we have the science to know with more certainty that 4.0- to 4.6-magnitude earthquakes present no danger to transportation infrastructure in the state. This change in protocol allows the department to better focus its resources.”

In addition to revising ODOT’s inspection protocol, the team was responsible for conducting detailed structural analyses of three ODOT bridges to assess their seismic vulnerability. Heinrich analyzed the I-35 bridge over the Cimarron River, and Kaid Bay Cortez analyzed the SH-11 bridge over I-35 as well as the I-35 bridge over the Canadian River. The results of the research also will be used to validate fragility values essential in the development of ShakeCast-OK, a real-time situational awareness program for post-earthquake response.

“This has been an incredible opportunity for the University of Oklahoma to play a central role in addressing a problem of state significance and national interest,” said Harvey. “My colleagues and I are very excited that we have been able to save ODOT time and money, as well as easing some of the concern surrounding Oklahoma’s earthquake activity.”