Evaluation of current rigging and dismantling practices used in arboriculture 　流纜繩子張力評估表

Evaluation of current rigging and dismantling practices used in arboriculture

Log mass estimate

Side 1:

1.Measure the (A) average diameter (in inches) and (B) length (in feet) of the log section to be dropped.

2.Using the values determined in step 1, turn the inner wheel to align the measured “Diameter, inches” with the measured “length, feet.”

3.Locate the tree species on the green log density chart, and note its density in lbs/ft3.

4.Locate this density value one the density scale at the top of the calculator wheel.

5.The estimated mass of the log section is the mass value off the “mass , lbs ” scale which is aligned with the density value of the tree species(determined in step 4).

Peak line load estimate side 2:

1.Determine the estimated mass of the log section to be dropped, on wheel side 1.

2.Measure the distance between the upper block and the center of mass of the log section to be dropped(where the rope should be tied-off). This distance is L1(see diagram).

3.Measure the total length of rope in the system between the upper block and the point where the rigging line is anchored or friction wrapped. This distance is L2 (see diagram).

4.Divide L2 by L1 and find this value one the L2/L1 scale.

5.Turn the inner wheel to align the estimated mass of the log (on the “mass of load, lbs” scale) with the L2/L1 value.

6.In the “peak line tension, lbs” window at the bottom of the tool, locate the row for the type and diameter of rope to be used in the rigging,  the peak line tension for the rigging operation is the value where the indicator line (in the center of the window) crosses this row. The color of the background at this value determines the action which may be taken.

A.GREEN BACKGROUND:
The peak line tension is below the working load limit(WLL) of the rope. (this result would be true, even if the rope is tied off at the anchor.)

B.YEEEOW BACKGROUND:
The peak line tension will exceed the working load limit(WLL) of the rope line if the rope is tied off at the anchor.
Accordingly, DO NOT CONDUCT A DROP UNDER THESE CONDITIONS, UNLESS the operator LETS IT RUN.

C. RED BACKGROUND:
The peak line tension exceeds the minimum breaking strength of the rope.
DO NOT CONDUCT A DROP UNDER THESE CONDITIONS.