JMG Consultants

What Is Seismic Bracing and Why Is It Needed?

During an earthquake, seismic forces are exerted on a building and the contents within. These forces act horizontally upon the structure itself, as well as on the floor mounted equipment, wall mounted equipment, the piping, ductwork, electrical conduit and other systems within the building. Typical supports for all of these systems are designed for the gravity, or vertical, loads but do not take into account the horizontal loading caused by earthquakes. Seismic restraints (i.e. braces) resist these horizontal forces and keep the systems in place and secure. The main purpose, then, of seismic bracing is safety; to minimize the loss of life and reduce the cost of damaged equipment due to an earthquake.

The damaging effects of earthquakes are of significant concern in many areas of the world. Earthquake damage to inadequately restrained equipment systems within buildings can be extensive. Equipment knocked off of its supporting structure due to earthquake related building movements can threaten both life and property. The cost of properly restraining this equipment is insignificant compared to the associated costs of replacing or repairing the equipment and to the cost of system down-time as a result of seismic damage to the building services.

Our engineering designs present restraint systems which serve to limit the movement of equipment and to keep the equipment captive, or fixed, during a seismic event. Proper utilization of these systems can reduce the threat to life and minimize long-term costs due to equipment damage and associated loss of service.

Resources

1. United States Geologic Survey has an excellent site that is constantly updated with information on worldwide earthquake activity, earthquake science and earthquake hazard reduction. The web site is provided by the USGS Earthquake Hazard Program as part of the effort to reduce earthquake hazard in the United States.

Visit: www.earthquake.usgs.gov

2. Building Seismic Safety Council develops and promotes building earthquake risk mitigation regulatory provisions. Seismic design maps can be purchased from this site.

Visit: www.bssconline.org

3. The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) advances the arts and sciences of heating, ventilating, air conditioning and refrigeration. It provides useful information on the seismic restraint of equipment, piping and ductwork. We recommend ASHRAE publication RP-812 – “A Practical Guide to Seismic Restraint”, which can be purchased from the web site.

Visit: www.ashrae.org

4. Vibration Isolation and Seismic Control Manufacturers Association is a professional organization of partnerships, companies and corporations who engage in the manufacturing of seismic restraint, vibration isolation and noise isolation products.

Visit: www.viscma.com

5. The Sheet Metal and Air Conditioning Contractors’ National Association, Inc. publishes “SEISMIC RESTRAINT MANUAL – Guidelines for Mechanical Systems”. This manual includes seismic bracing details for piping, sheet metal ductwork and conduit.

Visit: www.smacna.org