What if damaged precast concrete bridge columns and building beams or columns could be replaced instead of having to demolish the structure?
That is the possibility a South Dakota State University graduate student and his adviser are looking at. Kallan Hart is a first-year graduate student from Faribault, Minnesota, who earned his bachelor’s in civil engineering in 2019. Mostafa Tazarv is an assistant professor in the Department of Civil and Environmental Engineering within the Jerome J. Lohr College of Engineering.
Work has just begun on the project, which is largely being funded by an award from the Precast/Prestressed Concrete Institute. Hart received the $40,000 Dennis Mertz Bridge Research Fellowship for 2020-21 and became the first SDSU student to receive an award from the institute. It is to cover his tuition, fees and living expenses as well as project costs.
Supplemental funds come from the National Center for Transportation Infrastructure Durability and Life Extension.
They will undertake a two-year study within the Lohr Structures Lab on campus in cooperation with industry partner Gage Brothers Concrete, Sioux Falls.
Tazarv explained steel bars are traditionally embedded within the columns or beams of a concrete structure. However, when a catastrophic event, such an earthquake, hits the structures, those bars often yield, and sometimes buckle or fracture. When the damage is extensive, the entire structure must be demolished, he explained. Hart and Tazarv will experiment placing the bars on the outside of the bridge columns, which are the main source of resistance against earthquakes and other extreme events.
Their theory is that those bars could be replaced while leaving the structure in place and saving millions of dollars as a result.
In initial testing in the Lohr Structures lab, Tazarv said “the proposed repairable precast connections were investigated through cyclic testing of four half-scale beam-column specimens detailed based on a nine-story building designed for Los Angeles, which is a high seismic region. A reference cast-in-place beam-column specimen was also included for comparison.
The test results showed the repairable precast connections can withstand more than 14 times the design level earthquake with insignificant damage and ability to be repaired afterward.”
Furthermore, Tazarv found precast buildings using the repairable technology can withstand extreme earthquakes with minimal damage and repair need. Now, it is the time to test the idea on bridges.
In the next two years, Hart will develop 10 new repairable details for bridge columns, rank them based on constructability, cost and expected performance, and test the top two repairable columns, each 10-feet tall, to failure.
Hart is excited to begin the research and be selected for award.
"Assisting on work in the lab the past few months has given me new insight into the seismic applications of structural engineering, despite residing in a low-seismic zone. Hopefully, our new detailing will provide transportation departments and other bridge owners an additional design option to reduce replacement costs in the inevitable event of an earthquake in high-seismic zones while also cutting the amount of time that bridges will have to be closed to the public," Hart said.
Tazarv called Hart “a smart, outstanding and hardworking student. This fellowship will provide him an opportunity to perform an innovative research and also benefit from the industry partnership planned in the project.”