Mechanical analysis of tree spars in cable yarding systems

Abstract

Tree spars, as appropriate supports for cable yarding systems, have to be verified for the strength before any real operation. This paper gives theoretical analysis for various cases. Tree spars without guylines are normally under heavy bending stress, which dominates the strength design. For tree spars equipped with guylines, the spar deflection follows the same way as an unguyed spar. The overload of the bending stress remains the main reason of spar failures. Several diversities of tree spars from the idealized condition are investigated for the sake of better modeling of the real situation. Analysis supports that the tree spar can generally be treated as a straight cylindrical column without giving significant errors. The load can be handled as centrically applied. Design methods are provided for both guyed and unguyed tree spars, which will benefit the practice of using tree spars as an alternative for steel spars.