United States Department of Transportation
i
Remaining life assessment of in-service luminaire support structures : final report, January 2010.
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2010-01-01
[PDF-4.15 MB]
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OCLC Number:664685082
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Edition:Final research report.
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and Structures;NTL-SAFETY AND SECURITY-Highway Safety;
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Abstract:Recent fatigue failures of in-service luminaire support structures in Washington and around the country have
prompted concern about their fatigue resistance. Most luminaire support structures in Washington were designed
without attention to fatigue or with vague and incomplete fatigue design provisions. Furthermore, most luminaire
support structures were installed during the construction of the Interstate system in the 1960s, and as many as half
are estimated to have exceeded their 25-year design life. This research was initiated to help the Washington State
Department of Transportation (WSDOT) prioritize the inspection and replacement of luminaire support structures
throughout the state and to develop rational inspection procedures.
The research had four primary components: a literature review, experimental fatigue testing of two in-service
luminaire poles, a finite element analysis of the pole base, and development of a framework for estimating
remaining life. The extensive literature review found previous experimental studies, which were used to identify
details in older WSDOT luminaire support structures that may be critical and to help inform the selection of test
specimens. Quasi-static and high cycle fatigue testing were performed on two previously in-service luminaire poles
to determine the stress concentration factors (SCF) in critical details and determine fatigue resistance. The results
were then compared to the finite element analysis and the fatigue classifications used in design. The finite element
model was also used to determine the impact of parameters including base plate thickness, hand hole stiffener
thickness, and location of anchor bolts. The individual components of a framework for estimating the remaining
life of luminaire support structures in Washington were developed on the basis of a procedure established by Foley
et al. (2004) in their study of the remaining life of sign bridge structures.
The remaining fatigue life of the critical details in the previously in-service luminaire support structures were
found to exceed their design life. Cracking at the stiffened hand hole detail was found to be the ultimate limit state
for both specimens but was observed at cycle counts that were well beyond the design life. High SCFs were
measured in both compression and tension at the CJP weld toe, indicating the importance of base plate flexibility,
anchor bolt layout, and a uniform bearing surface. While it was not possible to know the load history for the
selected specimens, it is clear that the number of damaging cycles was low and that the fatigue design life for these
details is conservative. Recommendations for luminaire inspection are provided.
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