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NONSTRUCTURAL HAZARD MITIGATION:
By Guna Selvaduray, Ph.D.
To most people, earthquake damage
means collapsed buildings and freeway overpasses. These are structures.
But even if the structures are not damaged, buildings can be rendered
useless by damage to nonstructural components, including architectural
features, ceilings, partition walls, HVAC systems, and office or production
equipment. After the Northridge earthquake, at least one hospital closed
because of nonstructural damage. All patients were evacuated. Even minor
earthquakes can cause nonstructural damage to household items, office
equipment and production equipment. Secondary effects arising from nonstructural
damage include threats to life safety, fires and hazardous materials releases.
The first TV report after the Kobe earthquake featured a 74 year old man
killed by shifting furniture. Numerous hazardous materials releases have
occurred after earthquake ground motion. Some of these releases, especially
at university laboratories, have resulted in major conflagrations.
LACK OF UNIFORM CODE
The threat of structural damage is addressed in building
codes, especially in the US and Japan. The issue of nonstructural damage,
however, has received far less attention. Strict codes of practice do
not exist. There has not been uniform recognition of the issues with or
solutions for earthquake damage to building contents among the "bodies"
responsible for these codes.
FIVE AREAS OF MITIGATION
Nonstructural hazard mitigation can be very cost effective
and at the same time relatively easy to implement. The up-front cost for
design, fabrication and installation is small in comparison to the benefits.
This article will address hazard mitigation for five major groups of nonstructural
components: Office equipment, production equipment, warehouses, emergency
power and utilities, and glass. (See expanded article in the Online GUIDE
for information on issues not covered in this article.)
Office Equipment
Tall bookshelves, filing cabinets, desktop computers,
and similar items are most prone to damage. Bookshelves and filing cabinets
should be anchored to the wall studs (not drywall). The materials needed
include strong angle brackets, readily available in hardware stores, and
approximately one half to one hour per bookshelf. The office computer
is essential for most businesses. After the Kobe earthquake, several major
companies shut down because of computer damage. Sliding off desks is the
primary problem. Damage to printers and scanners, with low centers of
gravity, can be reduced by increasing the friction with the desktop—special
mats can accomplish this. Taller items need greater restraints, such as
strapping to the surface.
Production Equipment
It is more difficult to outline general rules
for production equipment, which comes in a variety of sizes and shapes.
Nevertheless, the most important general rule is to make sure it is anchored
to the structure, with anchor bolts that are engineered for the anticipated
ground accelerations. Installation of snubbers and other restraining devices
should also be engineered if adequate protection is to be provided. In
the case of equipment where alignment is important, such as motor-generator
sets with sensitive couplings, it is advisable to mount both the motor
and generator on a common base and anchor the base.
Warehousing Facilities
Most production facilities and retail outlets are dependent
on their warehousing facilities in order to conduct business. Since materials
are in transition, hazard mitigation tends to be overlooked. Referring
again to the Kobe earthquake, the most common locations with the worst
hazardous materials releases were warehousing facilities. Shelving that
has not been bolted to the floor will typically tilt, spilling contents
on the floor and blocking the passages at the very least. Direct damage
to shelving, especially from buckling or deformation of shelving components,
is also very common.
Prevention of shelving collapse is best achieved by:
• Strengthening shelving components to prevent buckling
and bending
• Anchoring shelving to floor
• Bracing the shelves together, and possibly to structural walls as well,
so that a new configuration with greater stability is created.
Emergency Utilities
The unavailability of emergency utilities such as power,
fuel, water and communications has also resulted in post-earthquake shutdowns.
If emergency power generators are installed, the battery set needed to
start the generator must be protected from earthquake damage. The same
goes for the fuel tank and the fuel lines.
Glass Protection
Glass damage to buildings and storefronts accompanies
every earthquake—even moderate earthquakes. Fracture of glass panes should
be prevented for the simple reason that chards flying out can cause serious
injury. Glass panes are also used to isolate one area from another inside
the building; most clean rooms in high-tech production facilities are
dependent upon glass to provide visibility while maintaining the environment.
Glass used for interior partitions can be replaced with other transparent,
but shatter-resistant materials such as polycarbonate. Where the glass
cannot be replaced, adhesive transparent films can be applied on the surface.
These films do not prevent glass fracture, but they do significantly reduce
dispersion of the fragments. In new construction, the use of wired glass
would reduce dispersion, though wired glass is generally more expensive
than plate glass.
Nonstructural hazard mitigation is extremely cost-effective
and very easy to implement. For many items, such as bookshelves and the
like, "self-help" approaches work very well and contribute to significant
hazard reduction. However, for more complex items, such as production
equipment and warehouse shelving, it is important to develop engineered
solutions to assure a valid improvement in safety.
About the Author
Guna Selvaduray, Ph.D. is professor in the College
of Engineering at San Jose State University. He can be reached via E-mail:
gunas@email.sjsu.edu
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