Virginia Tech Takes on Earthquakes

A team of Virginia Tech researchers, lead by Finley Charney and Mahindra Singh, are developing new guidelines for the performance of structures during earthquake events of all sizes. The problems, they say, with existing structural codes, are that they are only designed to take into account collapse prevention during a large seismic event. What is needed are design provisions that take into account the building’s performance under repeated exposure to smaller events.

To that end, Performance-Based Earthquake Engineering is the design process that assures a building’s integrity is ensured throughout its lifetime of exposure to the kinds of earthquake activity it’s likely to see. The buildings should be able to weather repeated exposure to small events, sustain moderate but acceptable damage during less-frequent medium-sized events, and avoid collapsing under infrequent, large-scale earthquake activity.

Charney et al recommend the incorporation of four classes of earthquake-resisitance systems into the structure of new buildings in areas at risk of damaging seismic activity. These include:

• Hybrid Yielding systems, where the components are designed to fail at specific, controlled times, allowing the energy of the earthquake to be dissipated safely,
• Standard Augmented systems, where the building incorporates damping mechanisms, aimed at dealing with the moderate-case vibrations encountered during an earthquake,
• Advanced Augmented systems, incorporating damping mechanisms and yielding devices, so the building can cope in a two-tiered approach, and
• Collapse Prevention systems, an active system that only comes into play during the most crucial moments of the largest earthquakes, described by the researchers as, “being analogous to an air bag in a car.”