ANSWER TO RIGGING QUIZ No. 24
Question 1: TWO tag lines should be used for this load.
There are no written rules that tell how many tag lines should be used to tag lifted loads. As a rule of thumb, use as many as necessary to adequately control the load in a desired manner.
For example, loads similar to a convection section need two tag lines to keep it square with the boom during hoisting and swinging. Also, if the hook is locked to the load block, tag lines will keep the load from rotating which will keep the hoist lines from spinning up.
Question 2: One tag line should be hooked to corner A of the convection section and laid out to the West along the North side of the lift crane. The other tag line should be hooked to corner B of the convection section and laid out to the West along the South side of the lift crane. See the Tag Line Plot Plan below.
With this tag line configuration, the riggers on each tag line will not have to walk as far (244 Vs 420) and only about half as fast as they would if the tag lines were hooked to corners C & D.
The major
benefit in using this tag line configuration is that both teams on the tag
lines can see each other and will be able to maintain about the same tension on
each tag line. Someone monitoring the convection section can keep it square
with the boom by directing one tag team
to pull a little harder and the other team to let off a little. This way, the tag teams are not trying to
out pull each other. In most cases, all
the two tag teams have to do is just hold their tag lines snug and walk slowly
to keep their tag lines square with the convection section.
Question 3: In this case the tag line at corner A should be hooked to the top of the convection section in order for the tag line to clear the top of the heater during swinging. The tag line at corner B should be hooked to the bottom of the convection section to keep the tag line as flat as possible.
Question 4: 200 minimum ((80 + 5 + 15)*2) for tag line A and 170 minimum ((80 + 5)*2) for tag line B. To be effective, tag lines should be at a 2:1 slope or flatter.
Question 5: ½ minimum. This was found by first solving for the friction force F between the thrust bearing on the hook shank and support plate on the load block. F = 65,000 lbs of convection section weight * .11 coefficient of friction = 7,150 lbs. The torque T = 7,150 lbs * 3 radius of the thrust bearing = 21,450 lb-in. The horizontal force H required to rotate the convection section = 21,450 lb-in / 240 half length of the convection section = 90 lbs. The SWL of a ½ diameter manila rope = 550 lbs., and is therefore plenty safe even when considering a mild wind.
A 1 diameter manila rope is recommended for a lift like this, as it is easier to hold on to. Also if the load control is real critical, is recommended that two tag lines be hooked at corner A and two hooked to corner B just incase one would come loose or break.
Question 6: Two minimum. A 150 lb. rigger can pull a force equal to his own weight if he is leaning backwards, has his feet firmly planted and the tag line is quite flat. The problem is that the rigger cant always firmly plant his feet, so the friction force between his feet and the soil is equal to .5 coefficient of friction * 150 lbs. = 75 lbs. Therefore two riggers can pull approximately 150 lbs. > 90 lbs. ==θ Okay
COMMENT ON TAG LINE USE:
In general, the use of tag lines is one of the most important and least understood operations in construction. In lifting operations where the load is high above the ground with very little clearance between it and the boom, there is usually mass confusion in keeping the load square with the boom. Everyone is hollering and running back and forth to pull first in one direction and then in another as the load sways back and forth. It doesnt have to be this way. Using a planned tag line procedure makes the lift go very smoothly without anybody getting nervous or upset. One person should be able to control the complete tag line operation by just using hand signals.
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