NUTS + BOLTS BILL DUNDAS CRUCIAL CONNECTIONS is a sign-industry consultant and the former manager of technical and regulatory affairs for the ISA. Email him at wsdundas296@gmail.com 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 J Because twin-pole signs are structural arches, their damping properties typically exceed those of singlepole signs. 30 SIGNS OF THE TIMES OCTOBER 2017 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 and durability. SINGLE-POLE CONCERNS An engineering research project conducted by the Intl. Sign Assn. (ISA) during the period 2008-13 (www.signs.org/ Resources/TechnicalRegulatoryResources/EngineeringandInstallation/SignStructureResearchExecutiveSummary.aspx) 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.http://www.signs.org/Resources/TechnicalRegulatoryResources/EngineeringandInstallation/SignStructureResearchExecutiveSummary.aspx http://www.signs.org/Resources/TechnicalRegulatoryResources/EngineeringandInstallation/SignStructureResearchExecutiveSummary.aspx