Strength Loss in Southern Pine Poles Damaged By Woodpeckers

Eighteen 50-foot, class -2 creosoted southern pine poles were broken in field tests to determine the effect of woodpecker damage on strength. The percent of cross-sectional area of wood removed at woodpecker holes ranged from 11.6 to 72.2 percent and averaged 39.0 percent. Two poles without damage and four poles which failed below woodpecker damage were used as control poles. Two methods were proposed to correlate the maximum fiber stress in bending with height in the pole; this maximum stress was then used in computing the capacity of damaged poles to carry lateral loads. The first method assumed that maximum fiber stress in bending was related to, height in the tree in the same pattern that extreme fiber stress occurs in a tapered class 2, 50-foot pole of minimum dimensions and loaded as a cantilever. The likely stress at failure at any distance from the apex and diameter was calculated by an equation. Since the equation gives a value of zero stress at the load point, an arbitrary stress value of 1000 p.s.i. was assigned to the upper two feet of the poles. A second method involved an adjustment due to specific gravity variation in a 50-foot pole. A linear reduction of stress from the 95 percent exclusion limit value of 4548 p.s.i. at the base to 2650 p.s.i. at the load point corresponded to a specific gravity decrease from 0.60 to 0.35. A further arbitrary reduction of stress of 50 percent was made at the top to adjust for knots and stress concentration. The final adjustment was made linearly from 4548 p.s.i. at the base to 1325 p.s.i. at the load point. Estimated load carrying capacity of damaged poles was calculated from the composite moment of inertia at the location of damage, the location of the centroid, and the adjusted values for fiber stress.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member