Seismic Shifts in ReliabilityEARTHQUAKE
How is reliability managed when the very ground underneath is unstable? Earthquakes and landslides are a fact of everyday life for New Zealand designers and engineers. This issue was readily apparent during a recent visit to Wellington and Parliament. While walking downtown, I observed a number of buildings marked with an “Earthquake Prone Building” notice and warning as shown in Figure 1. The posting warns the occupants and notifies the owner that strengthening or demolishing the building is required – though not for a while. This particular notice provided a 10 year deadline. Given the frequency and intensity of earthquakes, it appears to be a relatively generous timeframe.
In 2015 alone, New Zealand recorded over 37,500 earthquakes with eight quakes having a magnitude greater than 6.1 Table 1 shows the 55 year historical frequency of earthquakes with the “rule of thumb” guideline that magnitude 4 or greater quakes occur once per day!2
Figure 2 shows the data in a graphical form. Earthquakes around magnitude 6 are where building damage begins to occur. A guided tour of Parliament, the Parliamentary Library, and the Beehive drove home the earthquake infrastructure challenges even more. The photo below shows the exterior of these buildings.
New Zealand realized the vulnerability of these important buildings to earthquake damage and undertook a massive retrofit process to add a base isolation system. Base isolation reduces the transfer of earthquake forces from the foundations to the building above and reduces the need for extensive and intrusive strengthening concrete shear walls throughout the building. I was unable to take photos inside the buildings but images of this project can be found at www.parliament.nz/en/visit-and-learn/how-parliament-works/fact-sheets/earth-move. Four hundred and seventeen base isolator bearings were installed in the existing foundations under Parliament House and the Parliamentary Library and the buildings were separated from their .original foundations by a 20mm seismic gap. Installing the base isolators involved propping up the whole building section by section, cutting out large 7 ton blocks of the existing foundations and building new concrete foundations to hold the base isolators. Original foundations above and around the base isolators were strengthened by heavily steel reinforced concrete sandwich beams. It was quite impressive to see the scale of this retrofit!
Although New Zealand is at the cutting edge of seismic design standards, the nation has not yet solved the problem of finding all the potential ways a quake can occur and a building can fail. Models, building codes and standards continue to be revised as lessons are learned.3 While much of the focus is on building stability and safety, earthquakes pose a significant hazard to countries all over the world and to all kinds of electronic infrastructure.
Given our dependence on electronics in all types of mission critical systems, I found surprisingly little seismic guidance for the electronics industry.
The Electronics Handbook notes that seismic accelerations cause objects to make sudden drops under the influence of high G forces at very high speeds where “cables can be pulled loose, monitors can implode, and delicate electronics smashed into scrap.”4 Bolts, anchors, fasteners, and cabinets have been designed to protect everything from TVs and speakers to servers. Since electronics control many commercial, industrial and military applications, continued functioning during and after earthquakes is essential. Several standards exist to aid in the protection of telecommunication electronics in seismic zones including the Network Equipment-Building System (NEBS) requirements. Furthermore, in high seismic zones like California, for example, it is required by law that computer rack enclosures have earthquake restraints. Telcordia provides numerous NEBS standards and design guides for the industry while some companies choose to develop their own.
In the US, the Federal Emergency Management Agency (FEMA) provides some guidance for both telecommunications and electrical transmission facilities as well as administering the National Earthquake Hazards Reduction Program5 but given the age of much of the US infrastructure, there appear to be many vulnerabilities. John Ufford, a preparedness unit manager for Washington State Emergency Management Division, said electricity, communications and roadways are central to a 21st Century society. “Which of those are impacted by a massive earthquake?” Ufford said. “All of the above.”6 The American Public Power Association went so far as to consider earthquakes a “hidden disaster.”7
Given our dependence on electronics in all types of mission critical systems including electricity, water, gas, transportation, food, and medical services, I found surprisingly little seismic guidance for the electronics industry. The Southern California Earthquake Center at USC provides a very basic one page listing of consumer recommendations for TVs, computers, and electronics basically recommending securing them using Velcro, straps or bungee cords.8 The remaining advice focused on the use of rugged enclosures, racks and cabinets. It seems like there is significant opportunity for the industry to develop recommendations for both businesses and consumers on preventing, managing and recovering electronics from the hazards of seismic events.
Cheryl is a reliability engineering consultant with over 20 years of experience in electronics manufacturing focusing on failure analysis and reliability.
4. Whitaker, Jerry C. The Electronics Handbook. Boca Raton, Fla: CRC Press, 1996. Print.