Researchers at NC State are developing a way to construct bridges faster and make them more resilient against natural disasters. 

In a recent study, Department of Civil, Construction and Environmental Engineering (CCEE) researchers investigated a new type of structural connection used to reduce construction time, minimize traffic disruption and improve material quality.

The research team consists of:

• Julio Samayoa, postdoctoral researcher in the Department of Civil, Construction and Environmental Engineering (CCEE)
• Giorgio Proestos, CCEE associate professor
• Mervyn Kowalsky, Christopher W. Clark Distinguished Professor of CCEE

The connection, coined “external socket connections” by the researchers, will allow structural pieces to fit together quickly and seamlessly, almost like Lego pieces.

Through a series of large-scale experiments, the research team found the external socket connections to be resilient against seismic forces, or earthquakes. It’s a full-circle moment for Samayoa, who has dreamed of creating earthquake-resistant infrastructure since childhood.

“When I was 12 years old, there was a big earthquake in the town of my grandparents, and their house was completely destroyed,” the El Salvador native said. “That was impactful for me. As a child, I thought, ‘I would like to do something to fix this or to help these people,’ and that’s how I decided to pursue structural engineering.”

External Socket Connections

Socket connections are essential in accelerated bridge construction (ABC), an innovative approach to building bridges quickly and efficiently.

In a socket connection, a concrete column is embedded into a precast socket, or opening, within a structural element, such as a cap beam or foundation. The gap is then filled with cast-in-place concrete or grout, eliminating the need for additional reinforcement.

“The socket connections are external, meaning it’s outside of the other structural element, which is a beam or a footing,” Samayoa said. “Normally, those pieces were inside the structural element, which caused problems like congestion of steel during construction.”

This type of connection makes for quicker construction times, as it allows components to be prefabricated, or manufactured in a factory, and then transported to a site for easy assembly. Prefabricating components eliminates external factors, like weather, that can delay construction timelines.

Large-Scale Tests

The researchers conducted six tests to examine how the external socket connections hold up against earthquakes.

The large-scale tests took place at NC State’s Constructed Facilities Lab. The 20,000-square-foot research complex is home to extensive equipment, such as 20-ton overhead cranes and 25-foot tall column-testing frames.

“It would not be possible to do this type of research without the lab and the equipment that we have,” Samayoa said. 

Over the span of three years, the researchers ran earthquake simulations on six concrete columns, measuring roughly 7 feet 6 inches in height, with external socket connections. 

“We apply a force at the top, simulating the earthquake, and we test three times in one direction,” Samayoa said. “Then, we test three times for a specific force, and we increase the force, testing by three cycles, until failure.”

Through the experiments, the researchers found the external socket connections perform well against earthquakes due to its ability to dissipate energy, or ability to accumulate damage without failing abruptly. This adds valuable time during an earthquake to evacuate before any collapse.

“When an earthquake comes, you want the structure to move and to dissipate energy,” Samayoa said. “If designed properly, external socket connections can be used to reduce the size of a column to sustain the same earthquake a larger column could sustain. That means you can save money and use less material, having less impact on the environment.”

In Alaska, where the construction window consists of only a few months, engineers plan to build using the external socket connections in the next couple of years.

“It is rewarding to see that the research developed at NC State’s Constructed Facilities Lab can have a direct impact on real bridge projects and contribute to safer and more reliable infrastructure,” Samayoa said. “I feel proud knowing that these external socket connections can be applied not only in Alaska, but also in seismic regions around the world, providing confidence that the connections will perform as intended throughout the design life of the structure.”

This post was originally published in the Department of Civil, Construction, and Environmental Engineering.