Seismic Restraint is Really Important

Not just buildings are affected by seismic events but essential services located within the buildings can be majorly affected too if not properly restrained. We aim to ensure essential services in important buildings. equipment are adequately restrained so that the essential services continue to run even after a major earthquake.

Some reports note that at least 50% of the cost of damage to property after a major earthquake is due to insufficient restraint to secondary structural items or parts and portions such as suspended ceilings, air conditioning and ventilation systems, HVAC pipe work and computer data storage equipment. It makes sense to ensure that these items are properly restrained so as to minimize the damage and maintain the essential operational services necessary to keep your business moving.

The damaging effects of earthquakes are of significant concern in many areas of the world. Earthquake damage to inadequately restrained mechanical and electrical systems within buildings can be extensive. Mechanical and electrical equipment knocked off of its supporting structure due to earthquake-related building movement 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.

With a set of restraint systems which serve to limit the movement of equipment and to keep the equipment captive 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.

A thorough analysis of seismic restraint hardware and seismic rated vibration isolators requires the best consideration of:

1. The equipment must be securely attached to the restraint, and this attachment must demonstrate sufficient strength to withstand the imposed forces and to allow for transfer of seismic forces into the restraint.
2. Restraint Design: The strength of the seismic restraint must be sufficient to withstand the equipment imposed forces.
3. Attachment of Restraint to the Building Structure: This attachment is typically via bolts, welds, or concrete anchors. In addition, the building attachment interface must be reviewed to ensure that it is capable of withstanding the imposed seismic forces.
4. Equipment Fragility: The ability of the equipment to continue to operate after being subjected to seismic force. Fragility information must be obtained from the equipment manufacturer.

Review of Building Seismic Codes

The equations used to determine Seismic Design Forces are based on historical data that has been collected during past earthquakes. As the level of knowledge and data collected increases, these equations are modified to better represent these forces. Major shortcomings in the force levels predicted by the codes in effect at the time have led to the development of considerably more complex equations that more accurately address items such as equipment locations within a building, soil factors, etc.

The first code version significantly affected by the seismic data collected in the early 1990's was the 1997 UBC. Several new factors were introduced to the design equations to account for soil, fault proximity and type, specifics of the equipment location within the structure, and typical dynamic response characteristics for particular kinds of equipment. In 2000, the International Building Code or IBC was released. This new code was developed as a collective effort by the three independent code bodies. The IBC was intended to, and has been replacing the three independent codes countrywide.

It is important to recognize that the newer codes predict a significantly higher seismic design load than past codes. This is particularly true for equipment located in upper levels of buildings. In some instances using the newer code criteria it will be found that attaching heavy, unstable equipment located on an upper floor will not be practical with concrete anchorage. A connection directly to steel will be required.

Depending on the geology of the installation site, a vertical force component may also need to be considered when evaluating seismic loads. When incurred in the codes, this force is typically a fixed percentage of the horizontal seismic load.