a sign that is safe, practical, and durable is no small task
especially in a fast-paced, demanding business world
where everything is expected instantly. Speed should never
come at the price of safety and quality, especially when installing
and maintaining signage that thousands of people may look
at on a daily basis for a long time.
Public safety is the primary concern for any signage project.
To be safe, the sign and its foundation must be strong enough
to offset natural forces, or loads, that maycontinually challenge
Of environmental loads, which provide the greatest impact
on signage design, wind is often considered the most significant
because it can cause the most damage for the most geographic
areas. Ice and snow, on the other hand, are climate-specific
concerns. In cold weather areas with high snowfall, frost
heave, a condition in which soil with a high-moisture content
expands as water freezes, must be considered when determining
design requirements and selecting foundation depths for signage.
loading, the major damage-doer, occurs when a
rotational force, called a moment, is applied to the sign
and its foundation, causing the sign to pivot from its column.
The stronger the wind, the stronger the moment that weighs
against the sign.
If the engineer overseeing a sign installation does not accurately
account for wind loading, over time the sign may suffer from
fatigue stress damage, particularly in areas with frequent
high wind conditions. Fatigue stress damage can lead to structural
failure because it causes signs to keep bending back and forth
until they eventually weaken and fail.
Incorporating a decreased allowable stress level into the
signs design can prevent such damage. In areas with
constant high winds, such as Las Vegas or Chicago, it may
be beneficial to design for an even lower stress level than
what the local building code specifies, just to be extra cautious.
It is often assumed that once a sign is engineered and built,
it will last forever. However, lack of maintenance is a major
reason why signage structures fail to maintain intended longevity.
Signs should be regularly examined for weakened connections
and overstressed members by a qualified inspector with the
construction documents readily available to determine if original
design requirements were met accurately and to make any adjustments
for future maintenance.
Proper maintenance and inspection can help identify potential
risks for sign failure. Signs should generally be inspected
every six months to a year to identify potential problems
or risks imposed by the environment. In addition to wind damage,
other risks include corrosion due to water, salt, and acid
An inspector should be able to identify rusted or broken bolts,
corroded welds, and loose connections. The sign base needs
to be checked for proper drainage away from base metals. Pedestals
can be over-landscaped and buried and should be routinely
cleaned and maintained. Owners also should incorporate a routine
painting schedule as part of their maintenance, using rustproof
paint to keep steel and metal signs healthy.
Agost, P.E., is senior engineer for Structural Technology
Consultants, a structural engineering firm with a full-service
sign division located in San Diego (www.stcsd.com).