Putting Panels in Perspective

April 1, 2001
A Sign of the Times: Engineering safe, durable, and effective signage

Engineering 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 their durability. 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.Wind 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 sign’s 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 rain. 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.Mark 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).

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