The development and assessment of capacities for davit arms are crucia
l for uninterrupted electrical service, This paper addresses vertical
loads for davit arms, but the approach can be used also for horizontal
load capacity, The National Electrical Safety Code (NESC) method of d
etermining and assessing allowable capacity is based on ultimate capac
ity, and does not incorporate the variability of the population. Assig
nment of allowable capacity based on fiber stress and engineering anal
ysis is a rational alternative approach. In the example reported, glul
am davit arms were removed from service in eastern Oregon after 20 yea
rs. These arms were tapered/curved, glue-laminated timbers, and had be
en preservative treated by the Cellon(R) process. The population was s
ampled and tested to establish residual strength and load capacity. Tw
o davit arm geometries, with the principal difference in the radius of
curvature of the centerline, were evaluated. Statistical results show
ed that the bending stiffness of the two types was not significantly d
ifferent, but was lower than the original stiffness. Allowable load ca
pacities were established for the two configurations, and were compare
d to the original load capacities based on the grade of lumber used at
the time of fabrication. Results of the NESC method indicated that th
e arms no longer had the minimum overload capacity, and should be remo
ved from service. The developed allowable bending stress and engineeri
ng analysis provided the same conclusion. The confidence level assumed
during the determination of allowable stress was shown to affect the
results, and thus the potential decision for action.