Introduction
Earthquakes are not limited to California and The Discovery Channel. Neither are they infrequent; Weather Channel watchers know that seismic events take place on a daily basis throughout much of the continental western United States, as well as in Alaska. When combined with all the seismic activity that occurs on a global basis, scores, sometimes hundreds, of incidents of the earthquakes of a wide range of Richter values take place each day. It's only the Big Ones that make the front pages. And neither is California the sole prime seismic location in the U.S.; the New Madrid Fault, which runs through parts of Missouri, Tennessee and Illinois, has as much if not more kinetic potential than the much more widely known San Andreas Fault in Northern California. In fact, records indicate that it actually changed the course of the Mississippi River when a slip in the fault produced a massive earthquake in the 19th century. And residents of New York City, which is proud of its deep bedrock foundation, were surprised to read in the papers one morning earlier this year that Manhattan had experienced its own temblor the previous day.

The amount of seismic activity going on all around us, on a daily basis, is quite remarkable. And no one needs to be more aware of this fact than professionals who design, specify and install racks of equipment for audio, video, data and multimedia presentations. Those responsible for every type of structure, from sophisticated restaurants running paging systems, multi-zone music programs and house video; to mega-stadiums where computer-based multimedia systems run everything from audio at concession stands to the 60-foot scoreboard, need to understand what's required to meet the minimum standards which will keep them up and running - and safe - in the event of significant seismic activity. In many instances, millions of dollars of technology depend upon the quality of the racks they are stored in for their continued viability when Mother Nature gets riled.

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When is a Seismic Rating Needed?
All facilities classified as "essential" - i.e. fire and medical structures, police facilities, critical government agencies, etc. - must be seismically rated. Since those same facilities also require internal audio, video and data intercommunication, systems designers are increasingly interfacing with the architects and engineers who create and renovate such facilities. In addition, even facilities which don't fall into this classification, so-called "non-essential" structures, are implementing more and more highly sophisticated - and expensive - audio, video and data gear whose electronics would benefit greatly from the overall higher level of protection implicitly offered by seismically rated racks or enclosures.

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What Seismic Ratings and Standards are Used?
The guidelines for seismic ratings are derived from two sets of specifications established by independent organizations. The 1997 Uniform Building Code (UBC) is a refinement of a UBC specification issued three years earlier. That 1994 version was relatively general in scope, and broadly divided the U.S. into four geographical zones, of which Zone 4 - comprising most of central and coastal California - was rated the most prone to earthquake activity.

The other standard, the 2000 International Building Code (IBC) is considerably more precise: in addition to viewing the entire continent as a series of potential seismic locations, the specification has also resulted in maps that measure a given location's potential for experiencing seismic activity relative to an identified fault, along with probability maps for every 100-foot section relative to that fault's location. This enables seismologists to determine the "S factor" for a location - the degree of likelihood that that location will experience seismic activity. The two code specifications are different in philosophical approach, but are ultimately complimentary in practice; the IBC is in essence a more focused and refined view of the UBC. While the UBC as it was originally developed was somewhat rigid in its application, it also provided the basis for the calculations that determine a structure's rating. The IBC specification then allows the output of these calculations to be more precisely applied to physical structures taking into account but not limited to their geographical situations. Having this information, along with historical information about the severity and duration of previous seismic events, enables physical engineers and architects to determine the level of seismic resistance and endurance that equipment racks will require.

The project engineer (P.E.) involved in the design and construction of a facility is responsible for determining the rating of the facility, because the rating is applied to the structure itself (which is viewed as a system with numerous components). That observation then becomes part of the specifications of the bid put out for the job. But note well that it is the audio/video/multimedia systems designer/installer who is responsible for assuring that the enclosures and racks that will be used are ones that comply with and conform to any seismic specifications that the engineers and architects have laid out.

How do you know if the racking you're considering will withstand the seismic activity? The racking should come already evaluated, rated and certified for seismic applications. Middle Atlantic's products are rigorously evaluated and certified by a highly respected independent seismic engineering and rating firm. That same firm tested our MRK-4436 enclosure last February. The certified results from that evaluation showed that the MRK series enclosures are capable of withstanding the highest recordable seismic activity in an essential-facility environment with up to 1,000 pounds of equipment uniformly distributed in the racks. In fact, I want to use those tests to point out the fact that bidding on projects that have significant seismic implications need not be intimidating, precisely because products like Middle Atlantic's MRK and WRK come with the assurance that they're up to meeting the seismic challenge.

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Keys To Safe & Successful Racks
I also mention the tests because they underscore two critical aspects of racks in a seismic situation: installation of the racks - more precisely, the interaction of the rack and the physical plant of the building - and how equipment is distributed within those racks. Both of these considerations will have significant effect upon the performance of the racks and enclosures under stress.

To achieve maximum protection for equipment in the rack, and to comply with the code specifications outlined by the IBC and UBC, the rack itself needs to be properly and firmly anchored to the facility floor. In choosing fasteners, the type of flooring first needs to be determined - concrete, wood, etc. But choose the quality of the fastener with the same degree of care you would any critical component of any system. Fasteners with high shear rating and high tensile strength are the best choice. Quality fasteners combined with proper installation creates a synergy between the rack and the physical structure around it.

Though not as critical as the floor anchors, anchoring the top of the rack is also important. But there are additional efficiencies you can achieve here. For instance, if you anchor the top of a rack or enclosure to the side wall using a cable ladder, it reduces the tension load on the floor anchors to a measurable degree. That can act as an extra level of security in the installation process.

Other specifications determine how and to what extent a component within the rack or enclosure requires rear support. A unit must be rear-supported if all of the following three criteria apply:

1. The unit exceeds 10 pounds per rack space, and
2. The center of gravity is towards the rear, and
3. The overall depth of the unit is greater than 2.5 times the racking height.

In addition, rear support is required if the rack mounting ears of an individual piece of equipment are incapable of cantilevering the weight of the unit. Furthermore, if the unit flexes when it is pushed down or when the rear of the unit is lifted, rear-hanging or blocking will prevent the equipment from "whipping" during a seismic event.

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Rack Types
It's a good idea at this stage to point out that having an array of choices in terms of rack types is very desirable. Depending upon the type and amount of equipment, an installer may want a rack design that offers good capacity but which also allows significant space for cable management, such as Middle Atlantic's WRK series. Smaller areas benefit from racks designed for higher density storage, like the MRK series. Incidentally, all the racks in both the MRK series and WRK series are seismically rated to hold up to 1,000 pounds in an essential-type facility.

If you adhere to all the seismic guidelines, you can even certify racks that are designed to pull out to allow rear access to racked equipment- very useful as equipment gets more complex and has to be reconfigured more often. In fact, a large number of our sliding AX-S series enclosures are installed at the Getty Museum in California in what is a seismically rated job.

The trend over the last several years has been toward deeper, less tall components as more digital audio and video processing gear, which tends to be much lighter and more compact than its analog predecessors, has come to the market and been put into wider use by systems contractors. Companies like Compaq are marketing one-rack-space servers and control systems, which are less tall and deeper than previous systems, but just as heavy. What's happening is that as systems evolve, their weight is being redistributed. Racking has to keep pace with that evolution, and it is. We discussed center of gravity before. This is also crucial to maximizing the rack's protective potential and its resistance to seismic volatility. Keeping the center of gravity as low as possible puts less strain on both the footing and wall anchors. Thus, heavy equipment such as amplifiers must be placed at or near the bottom of the rack. The rule of thumb is easy and logical: the heavier the individual piece of gear relative to all the other equipment, the lower the placement. Anyone who has ever helped a friend pack a truck on moving day will understand this principle vividly.

In short, a seismically ready rack should always be filled from bottom to top and no rack space should be left unfilled with either equipment or a blank rack panel as this would take away from the support. During the assembly and installation process of racks and enclosures, it's important to ensure that all of the fasteners - both those fastening the enclosure system to the physical plant and the rack screws - be tight and remain tight. The fundamental reason for this is to make sure that the rack is assembled and remains square - even if it's assembled off site (one of the collateral benefits of a seismic design is that it travels well) - so that the torsion due to travel or misplaced weight does not distort this shape and keeps it - literally - in shape and ready to deal with the seismic challenge it was intended for. When the rack is properly squared, all of the side-to-side motion that a rack system will experience in an earthquake will travel right down to the floor. In fact, in a well-bolted enclosure system, the floor and to a lesser extent the walls actually become part of the enclosure system, and vice versa. This adds exponentially to the survivability of a enclosure system even in the most severe of seismic events. It's also suggested that the enclosure system's plumb be checked at installation.

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Summary
These are some of the major considerations to keep in mind in choosing the right rack system for the seismic circumstances that your facility resides in. The thing to keep uppermost in mind is that any system will only perform as well as its weakest link will allow. Racking may not be as glamorous or as technically fascinating as the equipment that those racks will hold. But it is the first line of defense that will keep that equipment - and the business of the clients of systems installers and designers - working without interruption in the event of seismic activity. Dollar for dollar, it's the best insurance a facility can buy.