Derivation of Nominal Strength for Wood Utility Poles

The designated fiber stress values published in the American National Standards Institute Standard for Poles, ANSI O5.1, no longer reflect the state of the knowledge. These values are based on a combination of test data from small clear wood samples and small poles (<55 ft (<17 m)) and field experience up to the time of adoption of the standard in 1965. A number of changes over the past 35 years require that the wood pole industry update the basis for the ANSI fiber stress values if it is to maintain a lead role in the utility pole market. Changes that will impact wood pole design include new data for larger wood poles, increased pressure from competing materials, and the evolving transition from Allowable Stress Design (ASD) to a reliability-based Load and Resistance Factor Design (LRFD) format. This paper presents an approach to updating the basis for deriving fiber stress values for wood poles, which will provide uniform reliability across class sizes as well as species. We review the current basis for ANSI fiber stress values and recent pole test data. Our work suggests that adjustments such as those for load sharing and moisture effects be considered load factors rather than material factors and recommend a method of calibrating the new LRFD format to the ASD approach.