| A probability-based design method for wood poles used in single-pole transmission structures is presented. Design may consist of establishing a maximum span for a given pole or determining the required pole class for a given span. The developed method, which is in a Load and Resistance Factor Design (LRFD) format, gives designers better control over the probability of failure of wood pole transmission structures while retaining much of the simplicity of current design procedures. The essential difference from current design methods is that design values of wind speed, ice thickness, pole strength, and pole stiffness are calculated from equations which include a target reliability index and a coefficient of variation for the appropriate variable. It is anticipated that future design guides for transmission support structures will provide the required target reliability indices and coefficients of variation.;Several methods of evaluating the probability of failure of wood transmission poles are presented, including second moment evaluation, Monte Carlo simulation, direct numerical integration, and the design point method. Direct numerical integration was selected for use in evaluating current and proposed design methods.;Current design of wood transmission poles is investigated through reviews of the National Electrical Safety Code, ANSI 05.1 "Specifications and Dimensions for Wood Poles," and the REA-Bulletin 62-1. Load models and analysis procedures which are more accurate than those used by current design methods are discussed. |
