There aren’t very many rooms in the world that can successfully reproduce the devastating effects of an earthquake. But come May 1, a laboratory on the University of Alabama campus may be able to do just that.
Work is under way to outfit the laboratory within UA’s South Engineering Research Center with what is called a shake table to subject building design codes and materials to nature’s wrath in a controlled environment.
“In essence, the table is a large piece of steel that moves back and forth and represents the motion of the earth. This particular table is designed to be used to collapse structures,” said John van de Lindt, professor and endowed chair of UA’s civil construction and environmental engineering program.
“We want to know the margin against structure collapses. We can’t know that unless we know exactly how these structures collapse.”
Some might argue that Alabama is an odd place for an earthquake lab. However, van de Lindt left Colorado State University, a place with a lot more seismic activity, to work at UA.
“We’re doing this work here because, from an educational standpoint, we’re educating global engineers,” he said. “The engineers we put out into the world are ready to go out and meet anything, and this is a global problem.”
Van de Lindt said once the lab is outfitted with the table, it will be one of a kind in the Southeast and one of no more than 10 similar laboratories nationwide.
With such capability, it should come as no surprise that the lab has such an imposing appearance. The ceiling of the lab reaches some 30 feet up, and just below it are twin cranes capable of lifting 15 tons, not to mention two more cranes capable of lifting 5 tons.
The 3-foot thick concrete floor of the lab is actually porous. Every 3 feet in all directions there is a hole in the floor that can be uncapped in order to anchor the shake table and other equipment used in the lab with long rods that descend into the basement of the facility.
Lining the walls of the lab are pipes capable of funneling 720 gallons of hydraulic fluid into the shake table each minute.
Van de Lindt said he designed the shake table himself. The system is composed of several steel blocks placed on rails attached to the floor. Those blocks are then fastened to actuators, the large rods that do all the shaking.
The table itself is solid steel, measuring 17 feet long by 17 feet wide and weighing in at 32,000 pounds, Van de Lindt said. It hasn’t arrived at the lab yet, but will be placed atop the steel blocks.
Once the table is in place, UA researchers can begin building structures and parts of structures atop it for testing. Van de Lindt said the table is capable of supporting structures of upwards of 50,000 pounds.
Van de Lindt said that what makes UA’s shake table system so unique is that it’s capable of doing hybrid testing that other labs can’t do.
A few yards away from where the shake table will be built is a pit measuring 10 feet deep, 10 feet wide and 10 feet long. Called the “soil pit,” it will allow UA researchers to not only test the effects of an earthquake on structures but also to measure its effects on soil or other foundations that lie beneath structures.
Researchers will build a foundation within the soil pit and attach an actuator to apply motion to it. Once the test begins, Van de Lindt said researchers can measure the response of both the structure atop the table and whatever is inside the soil pit, all while changing the motion of the shake table accordingly.
“It’s an extremely different test and something that hasn’t been done before,” he said.
Van de Lindt said this hybrid testing is important because it would shed light on whether or not design codes in earthquake engineering have been too strong or not strong enough.
“These design codes have been calibrated without the information of such a test that includes the soil information. It’s possible that these codes could be conservative. We could be building structures that are too strong. Some might ask how is that a bad thing, but that’s potentially a waste of money,” he said.
“But what is more likely is that we are not designing structures as safe as we could be.”
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