Preface
This is the third edition of CSA Standard O116, Power and Communication Sawn Wood Crossarms. It supersedes previous editions published in 1953 and 1961 entitled The Physical Properties of Power and Communication Wood Crossarms.
The need for this edition arose from the recognition that a common set of rules applicable to all suitable timber species, while maintaining fixed cross-sectional dimensions, resulted in the stronger species being degraded to the level of the weakest.
Two classes off crossarms have therefore been incorporated, based on average breaking stress as follows:
Class 1 - 5,500 psi; and
Class 2 - 4,400 psi.
These ratings have been determined through correlation of limited defects and supported by tests on Douglas Fir crossarms at the Forest Products Laboratory, Ottawa. They correspond with those for Douglas Fir and Jack Pine, respectively, when the strength ratios of ASTM Standard D245, Methods for Establishing Structural Grades for Visually Graded Lumber, for beams and stringers are applied to the rules of the 2nd edition. Good correlation is also to be found with the allowable unit stresses for select structural grades of sawn lumber as given in CSA Standard O86, Code of Recommended Practice for Engineering Design in Timber.
It must be emphasized that overload capacity factors appropriate to the conditions of use under consideration must be applied by designers of utility lines to convert breaking stresses to allowable unit stresses.
In consultation with the CSA Committee on Sampling Procedures, acceptable quality levels have been assigned to the various characteristics of crossarms for purposes of inspection. An Appendix on sampling, condensed from CSA Special Publication Z90, Sampling Procedures, has been added.
Other changes have been incorporated. Rules for knot measurement have been reworded to remove ambiguities, particularly in the case of knots oriented at angels to the crossarms axes. Overall crossarm lengths and pin and bolt hole spacings have been removed from the mandatory Clauses in recognition of the wide range of requirements in these features. Details of typical crossarms are given in Appendices for easy reference. Others may be specified by purchasers. This step favours reduced waste by providing manufacturers with greater latitude for accommodation to the characteristics of individual crossarm billets. Marking must now include the class of the crossarm. These changes, by providing manufacturers with greater latitude for accommodation to the characteristics of individual factors with greater latitude for accommodation to the characteristics of individual cross billets, will result in less waste.
This Standard was prepared by the Committee on Crossarms and Wood Pins under the jurisdiction of the Sectional Committee on Timber, and was formally approved by these Committees and the CSA Technical Council.
Scope
1.1 General
This Standard covers the physical properties and workmanship requirements of sawn wood crossarms for power utility use (3¾ x 4¾ inches) and communication utility use (3¼ x 4¼ inches).
1.2 Reference Publications
This Standard makes reference to the following publications, and where such reference is made it shall be to that edition of such publication as listed below:
CSA Standards C83-1964, Communication and Power Line Hardware; O80-1966, Wood Preservation; O86-1959, Code of Recommended Practice for Engineering Design in Timber; O124-1957, The Physical Properties of Power and Communication Wood Insulator Pins; Z90*-1967, Sampling Procedures (*Special Publication); ASTM¹ Standard D245-68T, Methods for Establishing Structural Grades for Visually Graded Lumber (¹American Society for Testing and Materials); CGSB² Specifications 105-GP-1-1964, Inspection by Attributes; 105-GP-2-1965, Guide to the Use of CGSB Specification 105-GP-1 (²Canadian Government Specifications Board).
