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:
- 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.
- Restraint Design: The strength of the seismic restraint must be
sufficient to withstand the equipment imposed forces.
- 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.
- 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.
-
Seismic Cable Restraint Connector.