An 80 ft tall, five-story concrete structure outfitted as a hospital is being tested on the outdoor shake table at the University of California San Diego. Researchers are hoping to determine how to design such nonstructural components as elevators and medical equipment so that a building can remain functional immediately after an earthquake. Courtesy of UC San Diego
A five-story structure, portions equipped as a hospital, is being tested on the outdoor shake table at the University of California San Diego to help engineers understand the response of critical structures and their potential for remaining fully operational after an earthquake.
April 24, 2012—Shake-table testing that is currently under way at the University of California San Diego on a five-story concrete structure—two floors of which are designed and equipped to resemble a hospital with life-saving medical equipment and a working elevator—is producing useful results so far, researchers say. But there are still several weeks of testing and perhaps as long as a year’s worth of data analysis to go on this innovative project.
Seismic testing began on April 16 to help engineers determine how the nonstructural elements inside of a building that is critical to the functioning of a community will react in an earthquake. Live video of the tests can be viewed at this site.)
The 80 ft tall building, complete with a roof-mounted cooling tower, was constructed on the world’s first outdoor shake table at UCSD’s Englekirk Structural Engineering Center, part of the George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES) system, which is funded by the National Science Foundation and comprises 14 research facilities across the country. The building is instrumented with more than 500 high-fidelity sensors—including 230 accelerometers and 50 strain gauges—as well as more than 70 cameras and several Global Positioning System (GPS) receivers. The unprecedented level of instrumentation is expected to produce a vast quantity of data that will help engineers evaluate current building codes and improve the design of critical structures.
“The things that keep a building functional are the lights, the power, the plumbing, the egress system, the HVAC (heating, ventilation, and air conditioning),” says Tara Hutchinson, Ph.D., a professor of structural engineering at UCSD’s Jacobs School of Engineering and the project’s lead principal investigator. “And when we refer to buildings that are critical to society, such as hospitals, they need these services to keep their lifeline support equipment functioning.” Hutchinson points out that in the case of a hospital or other critical structure, being able to maintain a building’s functionality during an earthquake is equally important to maintaining its structural skeleton.
So although many tests have been done over the years to determine how the structural framing of a building will withstand earthquakes of all sizes, few have examined how the nonstructural elements will react and how to prevent damage to those elements from resulting in the closure of an important structure. “Most nonstructural components are very vulnerable to damage or loss of function at much lower levels of seismic demand than the skeleton,” Hutchinson says. “In the Nisqually earthquake, for example, it was water damage that dominated building performance—buildings were shut for weeks and months due to extensive water damage.”
And although some tests have been conducted in the past on individual nonstructural elements, this test represents the first time that such a broad array of a building’s nonstructural components will be tested as a system, she explains. “The thing that is unique about this test is that it takes a look at these components at the system level and how they interact with one another,” Hutchinson says. “A good example of that is the plenum space above your head; within this space the HVAC, the piping, the sprinklers, and the ceiling system itself are housed. And from past earthquakes, we have seen what sprinklers can do to ceilings—the most dramatic damage can be due simply to, for example, the [sprinkler] heads popping off and water going everywhere.”
The test also represents the first time that a working elevator will be examined under earthquake conditions. Stairwells will be tested as well, and that’s important because “you are limited in what you can test in a lab” when it comes to stairways and elevators, Hutchinson says. “To test a stair or elevator system its most useful to consider the system spanning multiple floors.”
In this regard, having access to the outdoor shake table is invaluable. “It allows us to go vertical,” Hutchinson says. “We have virtually no limits on going up.” And the building can be large enough to simulate realistic occupancy levels, and to test such components as sprinklers systems that have both a horizontal and a vertical component to them, she explains.
For now the structure is situated on four high-damping rubber base isolators, a method of seismic isolation that is more common overseas than within the United States. Researchers chose to submit the structure to motions that simulate those actually recorded during real-life earthquakes to give them an accurate sense of how the structure will behave during the type of event that is likely to happen along the West Coast or in the Pacific Northwest regions of the United States. Over the past two weeks, the structure was subjected to motions similar to those experienced in Northridge, California, in 1994, and Maule, Chile in 2010. “We can report that these tests were very successful,” Hutchinson says. “There was very minimal damage,” which was what the researchers expected.
In the coming weeks the structure will be tested using motions similar to other real-life earthquakes, and when this phase of the research is completed, the structure will be lifted, the isolators will be removed, and the building will be fixed to the table and tested again using the same motions. “We will have nearly direct comparisons” of how the elements behave when the building is isolated versus when it isn’t, she explains. Hutchinson says they expect much more story drift—and more damage—without the isolators.
And after all of the earthquake simulation testing is completed, the building will be put through one final humiliation: it will be set on fire. Or at least select floors will be. Hutchinson explains that gas pipe failures often lead to building fires following earthquakes, and researchers from Worcester Polytechnic Institute want to determine how a structure that has already been compromised by an earthquake—possibly losing its fireproof coatings or sprinkler system functions in the process—will behave during such a fire.
Although the $5-million simulation will only last a few weeks, it could easily take a year to analyze all the data from the hundreds of sensors that are monitoring the building’s reactions, Hutchinson says. “Many of the nonstructural design codes are integrated into the building design codes, but they are relatively ad hoc, simplified procedures that lack a scientific basis,” Hutchinson says. “We do not know if they result in acceptable or unacceptable designs. Our goal is to take the data generated and at first, assess how robust those codes are, and then after that, determine how we can improve those codes. And not only the codes, but the construction practice.”
Researchers will also compare the actual results with those predicted by computer simulations to help improve the accuracy of digital prediction tools. Calibrated models can then be used to extend the variability considered in the experiment simulation, Hutchinson says. “We want to come up with new guidelines for modeling that can be really beneficial to both the research and design communities,” she says.