Combined bending and compression

Appendix F of AS 7000:2016 sets out the normative (mandatory) methods for assessing timber pole strength. Section F5.4 specifies the following equation, which must be satisfied when a pole is subject to combined bending and compression:

\(\left( \frac{M*}{\phi_M} \right) + \left( \frac{N*_c}{\phi_{N_c}} \right) \leq 1 \)

Because this clause is normative, it applies to all overhead line design. One of the required inputs is the vertical strength of the pole — a value that power utilities often do not publish. Without it, the check cannot be completed.

In Poles ’n’ Wires, if the vertical strength in the Poles database is set to zero, this check is skipped and a note is displayed in the Tipload results indicating that it was not performed.