Calculate forces on beam with hook

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Homework Help Overview

The discussion revolves around calculating forces on a beam with a hook, specifically focusing on determining the forces at points A and B. Participants are considering whether to analyze the beam as a whole or in parts, and they are exploring the implications of equilibrium in their calculations.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are discussing the method of calculating moments and forces, with some questioning the correctness of specific distances used in the calculations. There is also uncertainty about how to account for the geometry of the beam, particularly regarding a protrusion.

Discussion Status

Some participants have provided guidance on the principles of moments and equilibrium, while others express uncertainty about their calculations and seek clarification on specific values and assumptions. Multiple interpretations of the problem setup are being explored.

Contextual Notes

There are references to a figure that illustrates the beam and its measurements, which may not be fully clear to all participants. Additionally, there is mention of prior experience with regular beams, suggesting a potential gap in understanding the unique aspects of this problem.

kaffekjele
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Calculate forces on beam with "hook"

I have a beam which looks roughly like the attached file. The aim is to calculate forces in A and B. Would I have to look at AB and CDE independently, or could I proceed as "usual" by calculating the moment in A and proceed with forces calculation in x and y direction?
 

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  • Bjelke.jpg
    Bjelke.jpg
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You could proceed "as usual". The entire system must be in equilibrium, subsystems may not and typically will not be in equilibrium per se.
 


I've done the forces and moment calculations on the beam, but I'm a bit unsure if it's done correctly. Every force is working on the center lines according to the figure, so I might be missing something here. I'd appreciate it if someone could take a look at my calculations and perhaps give some input.
A better figure showing all the measurements is attached.ƩMA= 0 → B*6,3+F*sin 44,4*3,6 =0 (direction: counter clockwise.)
B*6,3+19,5*sin 44,4*3,6 =0
B= -7,796 kN

ƩFx=0 → Ax-F*cos44,4=0
Ax-19,5*cos 44,4=0
Ax-13,932=0
Ax= 13,932kN
ƩFy=0 → Ay+B-F*sin44,4=0
Ay+7,796-19,5*sin 44,4=0
Ay-5,847=0
Ay= 5,847
 

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  • 20130217_201938 (2).jpg
    20130217_201938 (2).jpg
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Last edited:


How did you get "3.6" in ƩMA= 0 → B*6,3+F*sin 44,4*3,6 =0? The distance from A to E is not 3.6.
 


That's one of the things where I'm not sure if it's done correctly, but what I did was add 2,2 and 1,4. I suppose the height has to come into play somewhere, but I'm not sure how. Up until now I've only been doing calculations on regular beams without any sort of "protrusion".(Sorry, I don't know the correct English term for a beam like this.)
 


The moment of a force is the product of the "lever arm", the force's magnitude, and the sine of the angle between the lever arm and the force. The lever arm is the distance from the point around which the moment is taken to the point of the force's application. In this case, the lever arm is AE. You need to find its length and the angle between AE and the force.

Alternatively, the moment is defined as a vectorial product of the lever arm and the force, which allows you to get around without computing angles and lengths.

You can use either method.
 

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