At the University of California a group of engineers are analyzing a lightweight steel-frame structure that is six-story high. The building is tested on the biggest external seismic shake table in the world. The objective of the experiment is to determine how well cold-formed steel buildings are able to sustain fires and earthquakes that may occur. As of date the six-story structure is the largest of its kind to be subjected to a shake table test.
The six-story steel frame building undergoes seismic testing on world’s largest outdoor shake table. (Credit: Erik Jepsen/UC San Diego)
The team is led by Professors Tara Hutchinson and Gil Hegemier, from the Center for Extreme Events Research at the Jacobs School of Engineering at UC San Diego. As part of the test, the building will be subjected to a number of earthquake simulations of varying and increasing intensity. After the earthquake testing the building will be tested to evaluate how it withstands a fire by researchers from Worcester Polytechnic Institute. During the period of tests, small drones monitored by UC San Diego researchers will be in the air mapping and determining the damage.
The funds $1.5 million funds from the project come from sponsors by industrial partners, foundations and government agencies, such as the California Seismic Safety Commission and other partners from the steel industry, the U.S. Department of Housing and Urban Development and insurance companies. Roughly $1 million has been sponsored to the researchers in the form of in-kind donations in order to outfit and build the cold-steel structure.
The California Seismic Safety Commission is charged with supporting research and education that improves the safety of the citizens of The State in the event of an earthquake. We were happy to support this innovative research studying how this type of construction, in increased use in California, can be made safer in the case of an earthquake or fire. This testing sequence illustrates how applying cost-effective partnerships effectively and new technologies such as drones and remote sensing can help reduce the earthquake risk to people and property.
Richard McCarthy, Director, California Seismic Safety Commission
More than 40 video cameras, 250 sensors, and one GPS system, provided by the Orbit and Permanent Array Center at UC San Diego’s Scripps Institution of Oceanography, have been installed and are to be used by the researchers to collect the data required during the tests. Some of the sensors used are even capable of detecting movements caused by the wind.
“What we are doing is the equivalent of giving the building an EKG to see how it performs after an earthquake and a post-earthquake fire,” said principal investigator Tara Hutchinson.
The team is interested in studying the effects of the stimulated tremors on the six-story lightweight steel structure during the test and the building’s condition after the temblor. The team also believes that due to its comparatively lighter mass, the building will perform well in the tests. After the test, the building will be subjected to tremors more intense than it was built to endure. This experiment will help the researchers understand where the building may fail and to study the structural response through computer models that can be used to anticipate the performance of the structures under different earthquakes.
The structure is designed in the model of a multi-family residential building. However, the researchers are extending the structure’s height, placing it 64 feet above the shake table platen. In 2013, a residential structure two-story high was tested on the shake table, and this was the largest structure to be tested before.
Shake then Fire
The seismic testing would involve subjecting the building to temblors of varying and increasing intensities. Earthquakes that occurred in California 1994 Northridge earthquake of 6.7 magnitude, the 1992 Cape Mendocino Earthquake of 7.2 magnitude, and the 2010 Maule, Chile Earthquake of 8.8 magnitude are the various simulations that are going to be created by the researchers.
After the seismic tests, the structure will be put through live fire tests. A team of researchers, headed by Brian Meacham, a professor at the Worcester Polytechnic Institute, will light pans of a liquid fuel called heptane to achieve a temperature of 1000°C which is nearly 2000°F. These fires will be lit in the sixth and second floors of the seismically damaged building. The damaged incurred will be evaluated using video cameras and temperature probes to ascertain how the fire protection systems are able to perform after the damage caused through earthquake in preventing the spread of smoke and containing the fire.
Unmanned aerial vehicles (UAVs) will be deployed during both the tests by Falko Kuester, a structural engineering professor in the Jacobs School. This will help to create a 3-D video and model to assess the damage. The data collected during the tests will help the researchers to evaluate the thermal profile of the building. This measure is taken to see if drones that are have heat-detection cameras can be used to locate survivors and evaluate the damage suffered by the structure after earthquakes and earthquake-induced fires.
Fire-Ignition Source Appliances and Shut-Off Systems
The building that is tested also has appliances like stoves and water heaters that may catch fire if they are moved excessively due to the tremors of earthquake. Funding for these appliances, unbraced and braced, have been provided by the Insurance Institute for Business and Home Safety and State Farm Insurance. By doing this, researchers hope to assess the effectiveness of the restraint systems. A smart device capable of detecting seismic waves has also been installed by State Farm, inside the building. This system must shut down others that can potentially cause trouble when the tremors reach a certain level.
Additional unique features of the test program
UC San Diego’s shake table is part of the Natural Hazards Engineering Research Infrastructure Network that is funded by the National Science Foundation and supported through a NSF grant of $5.2 million, for five years, to be used for the maintenance and operation of the facility.
For the first time a six-story building made of cold-formed steel (CFS) is being put to seismic tests. The structure is taller than other buildings made of CFS and containing non-structural components such as doors and windows. In the building’s exterior, CFS window and door frames and sheetrock padding that are used in residential constructions can be found.
This is also the first time a six-story CFS building will be put to a fire test after undergoing seismic tests.
The research is also the first of its kind to use UVAs to monitor a CFS building and engage in multi-spectral imaging to evaluate damages caused through earthquakes and fires.