Journal article
Evaluating the load capacity of glulam davit arms after 20 years of exposure
Forest Products Journal, Vol.48(7-8), pp.57-62
1998
Abstract
The development and assessment of capacities for davit arms are crucial 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 determining and assessing allowable capacity is based on ultimate capacity, and does not incorporate the variability of the population. Assignment of allowable capacity based on fiber stress and engineering analysis is a rational alternative approach. In the example reported, glulam davit arms were removed from service in eastern Oregon after 20 years. These arms were tapered/curved, glue-laminated timbers, and had been preservative treated by the Cellon® process. The population was sampled and tested to establish residual strength and load capacity. Two davit arm geometries, with the principal difference in the radius of curvature of the centerline, were evaluated. Statistical results showed that the bending stiffness of the two types was not significantly different, but was lower than the original stiffness. Allowable load capacities were established for the two configurations, and were compared to the original load capacities based on the grade of lumber used at the time of fabrication. Results of the NESC method indicated that the arms no longer had the minimum overload capacity, and should be removed from service. The developed allowable bending stress and engineering 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.
Details
- Title
- Evaluating the load capacity of glulam davit arms after 20 years of exposure
- Authors
- R J Leichti (Author)W K Savage Iii (Author)Jeffrey J Morrell (Author) - Oregon State University, United States
- Publication details
- Forest Products Journal, Vol.48(7-8), pp.57-62
- Publisher
- Forest Products Society
- Date published
- 1998
- ISSN
- 0015-7473
- Organisation Unit
- University of the Sunshine Coast, Queensland; National Centre for Timber Durability and Design Life
- Language
- English
- Record Identifier
- 99450647502621
- Output Type
- Journal article
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