Laminated Crossarms

Studies were made to evaluate physical properties of various designs of laminated crossarms with a view to the preparation of a single specification covering all types of crossarms in order to reduce production costs. Approximately one million new crossarms are purchased annually for the Bell System. The various types include exchange arms used principally for local distribution, carrier arms used on long distance toll, lines, joint-arms used on poles which carry electric utility lines as well as communication lines, and nonjoint arms used on poles carrying only Bell System equipment. The first laminated cross arms were mounted outdoors in 1947 in the Bell Lab. test plots at Chester, N.J., and Limon, Colorado. The laminated arms were at least as strong as solid Douglas-fir arms. By calculating the strength of a section containing one or more joints and comparing this with the calculated strength required at that particular location in the arm, it can be determined where a particular joint or combination of joints may be allowed. It is anticipated that manufacturers will be able to produce laminated arms economically under Bell’s specification.

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