Signs of the Times - October 2017 - 30
NUTS + BOLTS
is a sign-industry consultant and the former
manager of technical
and regulatory affairs
for the ISA. Email him at
Safety and durability of sign structures hinge on multiple factors.
UST as a chain is only as strong as its weakest
link, the integrity of an outdoor sign depends on
careful consideration of various design factors
and faithful execution of these details by the
sign builder and installer. Because outdoor signs are exposed
to a variety of punishing environmental effects including
cyclic wind-loading (i.e., repeated fluctuations of loads
Because twin-pole signs are structural arches, their
damping properties typically exceed those of singlepole signs.
SIGNS OF THE TIMES
and corresponding stresses applied to the structure), both
the general type of structure and the specific geometry of
structural connections have substantial impacts on safety
An engineering research project conducted by the Intl. Sign
Assn. (ISA) during the period 2008-13 (www.signs.org/
represents a prominent example of this relationship. A
key finding of the study is that single-pole sign structures
are susceptible to dynamic wind effects which, in certain
cases, may lead to structural failures. Specifically, the
research cites structural damping as a key factor impacting durability of these signs.
Because wind-actuated movements of single-pole structures are relatively unrestrained compared to double-pole
Periodic inspections of anchor bolts and base-plate
welds are essential for proper sign maintenance.