ISU Civil Engineering leads research for earthquake-resistant bridges

POCATELLO, Idaho (KIFI) - Drivers might be able to see a piece of groundbreaking concrete on Interstate 15 at Exit 80 in Fort Hall. It's thanks to the work of Idaho State University researchers.

The new interchange has a precast concrete pier supporting the 222-foot long and 88-foot wide bridge over the Interstate. Unlike cast-in-place piers, precast concrete components are cast off-site in controlled environments and taken to the construction site for final assembly. The pier is one of only a few like it in the Idaho.

"A precast pier system incorporates structural elements such as columns and girders in a Lego-like construction,” Idaho State civil engineering associate professor and principal project investigator Mustafa Mashal said. “The connections between the elements are crucial for seismic resiliency. They must be strong enough to resist forces and deformations during an earthquake.”

The first concept for the piers was created by Leonard Ruminski, a former bridge designer with ITD who now works as a senior bridge engineer for Burgess & Niple. Ruminski collaborated with Idaho State researchers and hypothesized that a concrete-filled steel pipe strategically placed in a critical location of the bridge inside the support would better disperse the enormous stresses put on the piers during an earthquake.

“At that time, the only method being used in Idaho for connecting a precast column with the pier foundation and pier caps required very precisely placed and proprietary couplers,” Ruminski said. “The precision needed to install the couplers was challenging and often resulted in construction delays. This new system uses only conventional materials and is much more straightforward to install, reducing amount of delays on a project.”

The piers started being large-scale tested in 2019 at ISU’s Structural Laboratory (SLAB). In the SLAB, Mashal and his students tested the idea, building 11-foot tall and 15-foot wide models and models of the more common cast-in-place bridges.

“The large-scale lab tests we carried out for this project were, and may still be, the largest ever conducted in Idaho,” Mashal said.

The team used a hydraulic actuator to see how much force each model could take and how the models deformed before breaking. The precast pier came out on top in the end. After a few promising tests, the precast pier was incorporated into the I-15 Fort Hall Interchange project's design.

“Constructing a bridge is a lengthy process, and it can have significant impacts on traffic and the Fort Hall Interchange is a stretch of the I-15 corridor that can have significant traffic delays due to construction,” Idaho Transportation Department State Bridge Engineer Michael Johnson said. “Typically, bridge piers take several months to construct and by using precast columns and bent cap beams, we were able to reduce this time to several weeks. In addition, most of the construction of the precast piers can be completed during lighter traffic hours, further reducing impacts on the traveling public and increasing safety for commuters and construction workers.”

The ISU research program was led by graduate students Corey Marshall, Ali Shokrgozar, Kathryn Hogarth and Jared Cantrell, former graduate student and current research engineer at Idaho State. The results were recently published in a paper created by Mahesh Acharya, doctoral candidate, Jose Duran, masters student, Arya Ebrahimpour, professor of civil engineering and co-principal investigator, Cantrell, and Mashal in the American Society of Civil Engineers’ Journal of Bridge Engineering.

“Thanks to the research performed by ISU, the new pier system promises to be adequate and quite superior in seismic performance compared to the conventional, currently used as a benchmark, cast-in-place piers,” Ruminski said. “The research results gave us enough confidence to incorporate this new system for the first time in the Fort Hall Interchange bridge replacement project, and I hope it will eventually gain in popularity in the upcoming projects in Idaho and other states.”

“It’s brought me tremendous joy seeing the research I contributed to in the real world,” Acharya said. “It’s motivated me even more, to work hard and continue my research into building effective concrete systems for structures in seismically active regions."

ITD funded a second research project at Idaho State in 2022 to investigate retrofitting precast and cast-in-place bridges with ultra-high performance concrete following an earthquake. Testing was done at the SLAB and finished in 2023. The researchers plan to publish the results soon. Mashal, principal investigator, Ebrahimpour, co-principal investigator, Cantrell, Hogarth and Manish Acharya are the members of the second research team.

“ISU has been a leader in precast concrete research and education in the country,” Mashal said. “We have several ongoing collaborations with industry partners and look forward to helping implement more novel precast concrete technologies that are both seismically resilient and durable."

More information on ISU's Department of Civil and Environmental Engineering can be found here.