On the definition of construction grades for wood pole power lines

Abstract

Wood pole power lines in Canada may be designed using either a deterministic linear (DLD) or nonlinear (DND) design method, or a reliability based design (RBD) method, as documented in CSA C22.3 standards. Both DLD and DND are based on the concept of construction grade. This paper is intended to compare these three methods through a fairly extensive parametric study. As a result, it is found that the RBD method as adopted by CSA and adapted by BC Hydro is fairly comparable to the original Grade 1 construction as defined by DLD. In addition, the current CSA Grade 1 definition as given by DND is generally more stringent than its original DLD counterpart. Therefore, a revised DND is recommended to better define construction grades for a nonlinear analysis. Per this method, different grades are defined by adjusting strength factors while keeping the load factor being unity, so that its definition of Grade 1 construction is consistent with the RBD method. From long run, construction grades may be defined following an RBD approach by adjusting design loads for different design return periods while keeping the load and strength factors the same (regardless of grades).