Researchers are testing the stability of commonly used structures by using the world’s largest outdoor shake table to simulate earthquakes. The series of tests, which began on Jan. 10, will measure the effects of earthquakes on three-story reinforced masonry structures, which are frequently used in apartment and hotel buildings.
The tests are being conducted at UCSD’s Englekirk Structural Engineering Center in Scripps Ranch. The shake table is a realistic simulation of earthquake conditions and will be instrumental in contributing to available data. It will also influence methods of analyzing structures, according to Benson Shing, the structural engineering professor leading the project.
The structure — made out of cinder blocks to fit California’s seismic standards — was tested on the shake table. The structures undergoing tests were designed in accordance to the requirements for buildings, which have changed over the years to minimize chances of collapse during earthquakes.
Shing said the tests have not yet concluded, but results so far are promising.
The tests simulate earthquakes modeled after the 1994 Northridge earthquake — which measured a 6.7 on the Richter magnitude scale — but will also simulate earthquakes up to 7.0 magnitude. This is the first time that current building structures, as well the structures present during the Northridge earthquake, have been tested under conditions of such extreme stress or on such a large-scale shake table.
The data will be incorporated into a larger database that is used to enhance the accuracy and precision of prediction tools and can be used to accurately simulate the performance of structures with similar designs but unique details.
“The structure performed very well,” Shing said. No significant damage has affected the structures as a result of the shake-table simulations. Although little of the resulting data has been announced, the testing website includes 11 live-action cameras currently streaming from the site of the shake table.
Due to the many lives that have been lost to earthquakes, engineers are attempting to make sure buildings are safer than the ones that have collapsed previously. Of special concern are the structures that serve the general public, such as hotels, schools, apartments and hospitals.
The project is funded by a $1.5-million grant from the National Institute of Standards and Technology through the American Recovery and Reinvestment Act program. The National Science Foundation is funding this testing through the Network for Earthquake Engineering Simulation (NEES) Program in light of recent concerns about the safety of such buildings.
Shing and his team are collaborating with earthquake engineers from the University of Texas at Austin and Washington State University as part of a national movement to help improve the safety of common building structures.
Part two of the project will begin at UCSD in early 2012, when Shing and his team will conduct comparable tests on a similar kind of building, a two-story, masonry structure with smaller windows.
These structures are more difficult to analyze, because current methods used by engineers do not reliably assess the effects of earthquakes. The lack of a standard prototype also makes analysis more difficult. Using the shake table on this structure can give engineers a more accurate idea of how it will respond to earthquakes.
