In the US it's pretty common that we have a surveyor sight up a tower crane mast. OSHA asks for someone Qualified to verify plumb. But what if I told you that most manufacturers don't want this data? They don't prescribe it. They don't control for it. It isn't repeatable. And they consider it junk data.
It's generally an old idea to shoot up a tower crane for plumb. Liebherr seems to like it for the first tower. The manuals don't indicate if they want it further. I have personally had a surveyor fail to get me the data. The horizontal measurement got Liebherr USA all the data they needed to sign off on the plumb condition of the crane. I do believe that Wolff likes the data point. They also have a 1:1000 requirement whereas everyone else I know of asks for 1:500. There seems to be a different approach at Wolff that I've never dug into. But everyone else that I know of controls the plumb at the base in the horizontal plane.
The horizontal to the vertical plane is a 90 degree transition. It tells you all you need to know about the vertical. It's possible to have a tower deviation from there, but we are going to be talking about a long standing tower as the current towers and manufacturing techniques have better control. In seven years of my last years in tower cranes I always controlled the horizontal and I've had zero needs to correct the plumb. The only issues have been caused by measuring in winds or due to obviously imperfect towers that can be found.
What I liked to do was take a digital level from corner to corner on a monoblock anchorage. it's four legs welded together not unlike a 5' tall tower section. Then you use screw jacks or bolts to level off of the concrete infinitely versus trying to get shims under the legs after three measuring rounds with a surveyor. I could set anchorages by myself in 20 minutes usually with a telehandler. And they would be perfect with this technique.
We need to get the codes changed to match between OSHA, ASME, and the States to accommodate how cranes are manufactured these days. Our practices should be to meet the manufacturer recommendations, and frankly ignore data outside of that. If the government wants to collect the data, great. It's not relevant to how this crane plumb is managed. For risk purposes, you can only follow the manufacturer. I had a crane that the surveyor was reading was out of plumb. The base was perfect. The reading was done the next day and that surveyor thought it was 50% of the threshold, or 1:1000. Weather and surveyor techniques are causing us to put cranes out of plumb to accommodate poor techniques. You don't want the risk of putting a crane out of plumb against the manufacturer recommendations to accommodate a 1960's rule. It's entirely that simple. If your technique on the base is right, the reading of the tower is not your issue. It should be noted this way in your contracts to protect yourself. "Crane Plumb will be controlled by the manufacturer recommended procedure." End of discussion.
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