Shaking up civil engineering

Patrick Laplace in the structures lab

Custom-designed shake table supports earthquake engineering lab's innovation and success

Patrick Laplace and his team at the Large-Scale Structures Lab (LSSL) have never been known to turn down a challenge.

Together with researchers from the University's nationally ranked civil engineering program, Laplace and the lab staff have pushed the boundaries of earthquake engineering, becoming the first lab to simulate a curved bridge under an earthquake and the first lab to test a four-span bridge.

So when faculty asked Laplace to modify one of the lab's existing biaxial shake tables so it could move vertically as well, he was ready for the challenge.

In fact, Laplace decided to go a step further, custom designing a six degree-of-freedom shake table from the ground up and overseeing its manufacture on site in the LSSL

Compared to the lab's biaxial shake tables, which only move in the horizontal plane, the six degree-of-freedom table not only moves horizontally and vertically but also rolls, pitches and yaws, allowing it to simulate the natural motion of a ship on the sea, for example.

That kind of added movement allows the lab to diversify the kind of test projects it can take on, including both large-scale research projects and qualification testing of equipment for manufacturers. The table allows manufacturers to test their products under a simulated earthquake conditions to ensure they meet state or federal codes.

"Basically we're providing a service to the manufacturers to improve the quality of their product, and that's really the end goal," said Laplace. "It's a test machine that tests other machines."

In order to provide that service, Laplace had to first overcome a number of manufacturing challenges himself. Using a range of modeling methods, Laplace simulated every aspect of the machine and its performance under a wide range of conditions. The modeling took over two years to ensure that the table could meet the rigorous standards required to qualify equipment for use in hospitals, schools and other critical sites.

"I had to make sure that my test machine doesn't influence their test machine, and that my test machine can test what they want and improve their manufacturing processes," said Laplace. "Most of my time on the six degree-of-freedom table was spent on the initial design and simulation. The intent was to numerically model everything about the machine before I had the first weld laid down on metal."

After designing the table, Laplace worked with a wide range of Nevada companies on the construction in manufacture, tapping into a range of diverse industries to source and construct the unique machine. For example, the 9ft x9ft steel platen that the test units ride on, was sent to a mining company in Elko to ensure that the top was machined perfectly flat.

"As far as possible I kept everything in Nevada, which worked out great," he said. "Only the actuators, the controllers, were bought from MTS out of Minneapolis, but those parts are so unique they had to be outsourced."

While the six degree-of-freedom table was designed to test equipment and machines, it also played a key role in the 2011 large-scale bridge project, led by Civil Engineering Professor Ian Buckle, that tested how a curved bridge, loaded down with trucks, stood up to forces from an earthquake 50% larger than the 1994 Northridge, Calif. earthquake. Having the fourth shake table available allowed the researchers to test at a larger scale than previously possible and obtain very realistic results of how an actual bridge would react in a strong earthquake.

"I had to make some modifications, but it worked out great," said Laplace. "Without it, the curved bridge project wouldn't have happened. We would have had to have done something different. So that was a major research project for which it was fantastic ."

To Laplace, that kind of flexibility and innovation is what sets the Large-Scale Structures Lab apart from other large-scale earthquake testing facilities.

"We will take any and every project, the most complex projects, and so far we have succeeded every time," said Laplace. "I think that's what's unique about our facility."