Problem With a Slewing Bearing Crane

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Discussion Overview

The discussion revolves around the mechanics of a slewing bearing crane, specifically addressing the forces and moments acting on the system due to various load configurations and heights. Participants explore the calculations related to radial forces, tension in ropes, and the effects of center of gravity on these forces.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant expresses uncertainty about calculating the radial forces and moments acting on a slewing bearing crane when loads are positioned at different heights.
  • Another participant suggests that if only vertical forces are applied, the radial forces may be zero, prompting questions about the conditions under which radial forces arise.
  • Concerns are raised about the effects of snatch-loads and wind, which could introduce large impulse forces that complicate the analysis.
  • A participant questions whether the tension in a rope would differ based on the vertical position of a load, indicating that the relative horizontal position is crucial for balance.
  • There is a discussion about converting forces into x and y components to analyze moments about the fulcrum, with some participants emphasizing the importance of defining coordinates and resolving forces.
  • One participant hypothesizes that a higher center of gravity would result in greater tension in the rope due to increased moment arms.
  • Another participant suggests a systematic approach to analyzing the forces and moments, recommending the resolution of vertical and horizontal components and the calculation of resultant moments.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the effects of vertical height on radial forces or the tension in the rope under different load conditions. Multiple viewpoints and methods for analysis are presented, indicating ongoing debate and exploration of the topic.

Contextual Notes

Participants mention the need to consider various assumptions, such as neglecting weight in some scenarios and the implications of center of gravity on tension calculations. There are unresolved mathematical steps related to force components and moments.

Herbid
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Dear All Masters

I have problem with slewing bearing crane.

My subcon made a crane that have a very high platform deck form slewing bearing.

They said it is fine and the height is not an issue as it is in lower place.

I know the higher the load from slewing bearing,
the bigger the force or moment works on it, especially in radial force,
like my pic attach.

But I don't know how to calculate the increasing of a radial force / moment that works physically.

Anyone can help?

Thanks.
Timbangan.jpg
 
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Vertical forces are balanced when ? Nm = 10 Nm
 
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But a radial force is bigger than if the scale of left right load is a horizontal straight and same length of line.
 
You appear to be loading the system with vertical forces only.
If that is the case, the radial forces will be zero.
What radial forces are you considering.
 
So if the vertical mast is higher than 100cm, let say as extreme as 1000cm (the weight is neglected),
it is still no radial forces acting to the right side of the hinge?
 
Herbid said:
So if the vertical mast is higher than 100cm, let say as extreme as 1000cm (the weight is neglected), it is still no radial forces acting to the right side of the hinge?
If the forces are vertical, or due only to gravity, then the moment applied at the slew bearing is only the horizontal distance from the bearing vertical axis, multiplied by the weight hanging at that point.
 
Don't forget snatch-loads and wind effects. A gust, micro-burst or partial sling failure may produce very, very large 'impulse' forces.

Um, there used to be a cautionary website documenting such civ-eng mishaps and mayhem, but it lost its server...
 
Ok case closed.

I just wonder from this picture:
241454


Is Tension in rope T, the same for hanging an anvil at Bottom Right (A),
or if we put it on Top Right? (B).

The hinge or fulcrum slightly off center to the left side.

Because now we have weight of big blue box.
is the center of gravity taking into account?

The blue box and black base is welded.
 
Last edited:
If the box is free to rotate about the fulcrum then T will be independent of the vertical position, A or B. It is the relative horizontal position that is important for balance.
Herbid said:
The blue box and black base is welded.
What is welded to what?
 
  • #10
Understand.
Blue box is welded to black base, or blue and black is a one single unit device.

Now if there is a 100N horizontal force acting to blue box in top left side like pic attach:
241495


Is Tension of Red Rope (T) the same for A and B condition?
 
  • #11
You must learn to convert all the forces to x and y force components, at specified positions in space. Then you can work out the sum of all moments about the fulcrum and find the tension in the red rope.
 
  • #12
Baluncore said:
You must learn to convert all the forces to x and y force components, at specified positions in space. Then you can work out the sum of all moments about the fulcrum and find the tension in the red rope.
I see.
I think B will create much bigger tension in T since its center gravity position is farther away (result as a moment?) from fulcrum than A.
 
  • #13
Your picture needs to be made into a diagram.
Start by defining the origin of (x=0,y=0) coordinates at the fulcrum.
Then specify the (x,y) position of attachments for the applied loads = forces.
Next resolve those forces into Fx and Fy components, which should be simple in this case.
Calculate the resultant moments at the fulcrum.
That will give you the tension in the tie.
 
  • #14
Baluncore said:
Your picture needs to be made into a diagram.
Start by defining the origin of (x=0,y=0) coordinates at the fulcrum.
Then specify the (x,y) position of attachments for the applied loads = forces.
Next resolve those forces into Fx and Fy components, which should be simple in this case.
Calculate the resultant moments at the fulcrum.
That will give you the tension in the tie.
I am about to start, but stuck when a center of gravity (mass?) is involved.
 
Last edited:
  • #15
A good method for analysing these problems is to,
Resolve all vertical force componets
Resolve all horizontal components
Take moments about any vertical axis.
Then you have three simultaneous equations which are easily solved.
 
  • #16
My calculation for B.I assume an extreme condition that the center of gravity is right bellow 1 ton anvil (for easier cal).
So I draw straight line as a lever from fulcrum to the that center.
241516


Skiip.
The total moment Inertia is:
Inertia of 1 Ton anvil plus (100N x cos a) x length of red lever.

Then Tension force in T is:
Moment in Red divide to length of black's lever.
 

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