faq's

Frequently Asked Questions

Q. My projects are located in areas that do not normally see Earthquakes and I have not had to restrain equipment before, why am I now being asked to do so?

A. In reviewing seismic events on a worldwide basis, it has been found that a tremendous amount of damage has occurred as the result of only moderately sized earthquakes in low seismic areas (where little or no seismic protection was incorporated during construction). In addition, as the stresses in the earth’s crust increase with time, many areas with infrequent earthquakes have also suffered when larger events have finally occurred. This has been deemed unacceptable by FEMA (Federal Emergency Management Agency), the regulatory group that is driving the code requirements.

Q. In the past, although the code specified some requirements for minor seismic restraint where my projects are located, the code officials frequently waived the requirement. Why have they suddenly become stubborn about waiving it on current and future projects?

A. FEMA, besides being the driving force behind the codes, is also the agency responsible for relief when an "act of god" event (such as an earthquake or hurricane) occurs. Over the last 10+ years, the relief dollars that were spent far exceeded expectations and one of the key findings was that the damage costs would have been reduced significantly, had the rules in place at the time of building construction not been waived. Insurance companies have also been pressuring localities for better enforcement as they have lost literally billions of dollars during recent earthquakes.

Q. If I follow the current code standards, will my building weather an earthquake without any problems?

A. The codes are based on the maximum "likely" earthquake that has a 10% chance of occurrence in the next 50 years. (There is a very small chance that an earthquake can occur that is larger than this.) The codes are also "life safety" based. This means that during the above earthquake, the building and equipment will hold together well enough so that lives will not be lost. There is no requirement (except in some rare cases in hospitals, etc) that the building and equipment will retain its functionality. If continued functionality is required, a performance-based specification should be considered. (Note: A performance-based spec will typically require that all of the equipment specified for the project be shake tested to levels consistent with the design seismic forces to ensure its continued functionality.)

Q. The seismic design forces have greatly increased with the advent of the current code in my area. In addition, there is a lot more information that I need to have to determine what force is appropriate. Why is this?

A. During the 1989 and 1994 earthquakes that occurred in California, considerable information was gathered that had not previously been available. When experts reviewed this data, it was found that factors such as soil type, proximity to a known fault, and equipment elevation in a building had a significant impact in the actual forces. The force equations were modified to take this into account.

Q. Why do I not have to restrain piping or ductwork that is hung 12' or less from the ceiling?

A. Items that are hanging on supports react to earthquakes act as though supported on a pendulum. If the pendulum is 12" or less, its natural frequency is outside the range generated by earthquakes. Because of this, the piping and ductwork will move back and forth during an earthquake, but the motion will not be amplified with time. As long as there is nothing that won’t prevent 3-4' of lateral motion and the hanger rod is allowed to swing freely (includes some kind of swivel), pipe/duct systems have consistently survived seismic events with minimal problems. If this motion is restricted by local obstacles, damage can occur and the system would require restraint.

Q. Why do I need to provide restraints on equipment that is hung 12" or less from the ceiling?

A. While from a philosophic viewpoint it would seem that it would perform similarly to the ducts and pipes, there is not enough data to back this up. Because of this, the exclusion does not exist in the various building codes for equipment at this point.

Q. The mechanical equipment is all located on grade outside the building or in a central plant. Do you still have to have earthquake restraints?

A. The location of the equipment does not change the requirement for seismic bracing. However, the design forces that we must resist will change based upon the location of the equipment in or around the building structure.