Earthquake network sensors may improve building safety

Researchers at the University of California, Los Angeles (UCLA) are developing testing and monitoring equipment that will serve as the ‘eyes and ears’ of an earthquake engineering research network in the US.

The George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES), an $87 million project funded by the US National Science Foundation, brings together 11 institutions in a co-operative network that will allow them to share data and equipment.

Eventually the network will allow researchers to observe and sometimes even participate in experiments as they are being conducted in other parts of the country.

The field-testing and monitoring equipment being designed at UCLA’s Henry Samueli School of Engineering and Applied Science will provide researchers with real-time information on what happens to structures such as buildings, dams and bridges during simulated earthquakes.

According to Professor John Wallace of the civil and environmental engineering department and principal investigator on the project, sensors capable of monitoring up to 100 different conditions, including acceleration, strain and displacement will be placed in the buildings and the soil surrounding the buildings.

Information from these sensors will be transmitted wirelessly to a mobile command centre that, in turn, will transmit the data via satellite to the Internet. That way, other researchers elsewhere in the country ‘will be able to read our data almost as quickly as we can,’ Wallace said.

UCLA researchers were chosen to build the field-testing and monitoring equipment because of their expertise and previous work in this area and because its frequent seismic activity makes Southern California an ideal environment for developing and integrating the testing equipment, Wallace said.

By attaching large masses to a roof or floor of a building, and then using control systems to rotate these masses, the researchers will be able to exert forces up to 200,000 pounds and use the sensors to measure how the structure shakes.

In addition to the rotating shakers, Wallace said, they will also be obtaining a ‘linear shaker,’ which creates a random vibration pattern more typical of what you would see in an earthquake, but has lower force capacity.

By using different types of shakers, Wallace said, researchers will be able to create ‘small-to-moderate, and in some cases, significant building vibrations’ to address a spectrum of important issues relating to the response of structures to earthquakes.

Along with new buildings and those being remodelled, Wallace said, they also hope to experiment on structures that are to be demolished – some of which they may destroy in the process.

With the number of sensors to be purchased, and the use of wireless data transmission Wallace envisages being able to provide relatively dense instrumentation to obtain very detailed information that is not currently available.

Many of today’s computer simulations or laboratory tests are done on what Wallace calls ‘idealised buildings,’ which are the simulations that do not include a realistic model of the foundation system, or the influence of partitions, windows or the exterior facade.

Using real buildings as a laboratory has the potential to greatly improve the accuracy of these computer simulations, claimed Wallace. And more accurate simulations will reduce the loss of life and property by producing safer buildings that can better withstand earthquakes.

In addition, the researchers will use the equipment to vibrate a number of structures and catalogue the results so that in the event of another earthquake, the sensors can be quickly reattached to measure the vibrations during earthquake aftershocks.

Because the equipment is mobile, it can be moved to the site of earthquakes throughout the region and lent to other institutions. Sharing equipment as well as data are major objectives of the project, said Wallace. This way, all interested researchers will have access to a vast array of equipment and data.

Instead of providing funds to institutions to purchase the same equipment – which duplicates not only purchase costs, but also those of maintaining the equipment and training people how to use it – this program provides funds for special equipment to be housed at each of 11 national laboratories.

Access to the equipment at all NEES sites will be under the control of a consortium, which is under development, Wallace said. In theory, the equipment at all sites will be available to anyone conducting National Science Foundation -sponsored research, and possibly for research sponsored by others.

Once the program is fully operational, it is envisioned, for example, that a bridge column could be tested at one location, while a footing is being tested at another site and a model of the bridge is being analysed at yet a third location.

‘All three of these components could be run simultaneously and the resulting data updated at all locations in near real time,’ concluded Wallace.