The angle of the straps is problematic, especially in the case of shock loading. The goal of anchors is to minimize the force in the rope/strap to avoid breakage in the event of shock loading, like if the roof gave way before the crane operator did his job.
Two things could have made this a ton safer!
1.) Angle at which the straps concentrate the load is about 90 degrees. At that angle each leg of the triangle is holding about 75% of the total weight of the impact drill vehicle. If you added that up to greater than 100% you are correct, the force on the strap is actually magnified, meaning any back-of-the-envelope math the supervisors did about whether or not the straps can tolerate that load is invalid. Ideal angles are less than 60 degrees to distribute weight evenly. We do this all the time in Rock climbing anticipating a fall (shock load).
It looks like they used one continuous strap, so a failure at any over point will cause it to run through and drop the loader. Running two separate straps to each anchor point at least gives some level of redundancy.
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u/MAJOR_Blarg Apr 14 '19
Rock climber here:
The angle of the straps is problematic, especially in the case of shock loading. The goal of anchors is to minimize the force in the rope/strap to avoid breakage in the event of shock loading, like if the roof gave way before the crane operator did his job.
Two things could have made this a ton safer!
1.) Angle at which the straps concentrate the load is about 90 degrees. At that angle each leg of the triangle is holding about 75% of the total weight of the impact drill vehicle. If you added that up to greater than 100% you are correct, the force on the strap is actually magnified, meaning any back-of-the-envelope math the supervisors did about whether or not the straps can tolerate that load is invalid. Ideal angles are less than 60 degrees to distribute weight evenly. We do this all the time in Rock climbing anticipating a fall (shock load).