Scientists at the University of Nevada, Reno have started to test new bridge designs with connectors that are meant to better withstand violent earthquake tremors. They also believe that their innovative approach will be able to speed reconstruction efforts after major earthquake damage.
For the researchers, these tests couldn’t have come at a better time. They were conducted one day after a deadly quake hit Mexico, and their goal is to help prevent any fatalities as a result of falling structures.
Even though bridges are designed to withstand earthquakes, they often become unstable and unsuitable for travel after they have been hit by one. And considering that over two hundred million trips are taken daily across deficient bridges in the United States’ 102 largest metropolitan regions, a lot of people are putting their lives at risk every day around the country without even realizing it.
Saiid Saiidi is a researcher with the Nevada Earthquake Engineering Lab and has over 30 years experience looking at the structural soundness of bridges across the world. According to him, it is important to focus on creating a strong bridge in the first place since earthquakes don’t necessarily kill people, but unstable structures do.
To perform their experiments, the Reno researchers used a giant shake table to stimulate the violent motions of an earthquake. Their model weighed 100-tons and was 70 feet long. During the shake test, the columns and beams swayed back and forth for 30 seconds at a time — some were displaced nearly a foot, and others had small cracks in them. The graduate students studying on the project were able to use an electrochemical fatigue crack sensor system to detect cracks in the bridge as small as 0.01 inches.
However, they found that these fractures were minimal and didn’t result in major structural damage. This came as a surprise because the computer models they used before the test indicated there would be more bridge damage.
So what did the researchers do to create such a strong bridge? They used special connectors to link pre-fabricated bridge parts, including ultra-high performance concrete. These connectors cause the designers to place the prefabricated concrete directly onto the existing bridge foundation, making it easier for repair after a quake if necessary because they will be easier to get to.
Known as pipe pin connectors, the pin is made up of a steel pipe that is anchored into the column and extended into a piece of steel that is embedded into the bridge’s beam. But since there is a gap between the steel pipe and the piece of steel in the beam, the extended segment of the bridge is able to rotate freely during a quake. This flexibility means easier movement and less of a probability that the column will collapse on itself and crumble the entire bridge.
These special connectors make this bridge the first in the world that uses flexible columns and reinforcement bars made out of a metal alloy. While alloy steels can be divided into four classes: structural steels, tool and die steels, magnetic alloys, and stainless and heat-resisting steels, this metal alloy is made from titanium that bends and springs immediately back to shape after an earthquake hits.
The researchers at the quake lab are hopeful that this new technology can help earthquake-prone areas like the Western United States and Mexico in stabilizing their bridges for the future. As of right now, the California Department of Transportation is funding the project and is developing 10 projects with this new pipe pin connector technology.