Rack: Secure rack against seismic events
At this testing facility, the goal of seismically engineered rack is to make it able to absorb the shock caused by a seismic event.
February 01, 2012 - MMH Editorial
Terra firma isn’t all that firm. Every minute of every day there’s an earthquake rumbling beneath the surface of the earth. In fact, the United States Geological Survey (USGS) locates about 50 earthquakes daily, or 20,000 annually. However, it estimates that millions of earthquakes go undetected each year because they happen in remote areas of the world or measure such a small magnitude on the Richter scale.
Those earthquakes aren’t the ones that worry us.
And they happen in all states, not just California. From Alaska to Alabama, Oregon to Ohio, an earthquake can hit anywhere at anytime.
“The earth is always shaking and moving,” explains Sal Fateen, a structural engineer and the president of Seizmic Material Handling Engineering. “It’s actually a good thing for the earth to release tension, but the problem is that nobody knows exactly when the earth will decide to misbehave.”
That erratic behavior can wreak havoc with our warehouses and distribution centers if we aren’t prepared. Rack systems that support the materials handling industry are particularly vulnerable to damage caused by seismic events. But, there are strategies and solutions that can protect people, property and products.
Identifying high-risk seismic areas, conducting inspections, and keeping rack equipment in good repair can help minimize the damage caused by an earthquake.
Over the years, high- and low-risk seismic zones have been identified based on history and testing. Being in a low-risk area, however, doesn’t guarantee you’ll be spared. For example, in October of 2011, low-risk southern Texas experienced a 4.8 magnitude quake.
Still, the zones are a valuable guide. “When we consider seismic forces, we reference the zip code of where the rack will be built, and, depending upon the area, significant upgrades may be required to comply with the seismic forces,” explains Bob Novak, area market manager for Interlake Mecalux.
But because every rack installation is unique, there are no hard and fast rules for specific upgrades in any particular area. According to Dave Olson, national sales and marketing manager for Ridg-U-Rak and president of the Rack Manufacturers Institute (RMI), highly refined values for specific locations, which are publicly available, weigh heavily into rack designs. And, along with the rack structure height, depth of the frame, load weight, application, and type of rack, these values play a vital roll in seismic consideration.
The purpose of the identifying high-risk areas and establishing building requirements within those areas, however, is not to “earthquake-proof.”
According to Fateen, that’s not possible. The purpose is to minimize the damage that may occur from an earthquake. “It all boils down to developing a force that gets applied to a structure. Once you get that force, you have to develop equipment that can stand up to the test,” he says.
The force is calculated using a formula that includes a number of factors. While the calculations are extremely complex, Fateen explains, the force is a percentage of the weight of the structure and the load it carries. The rack structure has to be designed to resist the forces applied to it, including seismic ones.