Beam with a rope - type of problem (Statics)

In summary, it seems that you are using a different system than the normal convention and it works for you.
  • #1
goodOrBad
25
2
Homework Statement
In the image there is a beam I had to solve (reaction forces and moments in the points), I solved it but I do not know if the work is good so I need someone to check it.
Relevant Equations
Fx=0 -> +
Fy=0 ^ +
Given: 6kN at point A at 30deg, M=3000Nm but I changed the direction to make it easier so M=-3000Nm
the whole beam is 19m long.
Anyway I got
FD=3733.737 N
FBx=3056.360 N
FBy=-5400 N
bem.jpeg
 
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  • #2
Hi @goodOrBad and welcome to PF.

:welcome:

I cannot evaluate your work as either good Or Bad because I cannot read what you have posted. Maybe it's because of my tired old eyes, maybe it's because of the small characters maybe it's the poor contrast. Please consider that if you want people to help you, you need to make it easy for them to do so.
 
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  • #3
Your answers all look correct, except that you quote too many significant figures. As a result, you got 26.99... kNm for the moment about B, when it should be 27kNm exactly (6 kN sin(30) x 9m).
 
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  • #4
Yeah I will keep that in mind, thanks
 
  • #5
kuruman said:
... Please consider that if you want people to help you, you need to make it easy for them to do so.
✅

Welcome, goodOfBad :cool:

Are you studying Structural engineering?
I ask because the choice you made for the moment’s diagram, where moments look all negative.
The normal convention used in most engineering applications (other than for concrete structures) for a positive bending moment is to warp the element into a smile shape (compression at the top of the beam and tension on the bottom).

The way you assigned negative numbers to the distances in the summation of moments equation seems confusing (unless you have been taught that method).
I prefer assigning the sign to each moment according to the direction of rotation of each force-distance combination.

All your numerical results look good to me, except the moment diagram at the point moment.
It seems to me that, moving left to right, the moment should change from 27 000 N-m at point B to 17400 N-m at point C, where it should drop to 14 400 N-m and then reach a value of zero at point D.
 
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  • #6
Thank you for the feedback.

It is Mechatronics so there are some elements of Structural engineering, we have this class called Statics, and yes, you are right, it first goes to -17400 Nm then to -15000Nm I only spotted that some time after.

Since I like to watch everything from left to right and I use that the left from right as + when it comes to the x direction forces, I also like to go from point to point when I do moments in that direction.

I found the negative distance thing much better than flipping the drawing or thinking about directions the smaller the possibility of something going wrong the better.
 
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  • #7
You are welcome. :smile:

It seems that your personal system works for you.
I learned a different method many years ago; therefore, newer approaches confuse me some.
Best
 

Related to Beam with a rope - type of problem (Statics)

1. What is a beam with a rope problem in statics?

A beam with a rope problem in statics is a type of problem that involves analyzing the forces acting on a beam that is suspended by a rope. This type of problem is commonly used in engineering and physics to understand the stability and equilibrium of structures.

2. How do you approach solving a beam with a rope problem?

To solve a beam with a rope problem, you first need to draw a free-body diagram of the beam and identify all the forces acting on it. Then, you can use the principles of statics, such as Newton's laws and the equations of equilibrium, to determine the unknown forces and solve for the desired quantities.

3. What are the common assumptions made in a beam with a rope problem?

The common assumptions made in a beam with a rope problem include: the rope is massless and inextensible, the beam is rigid and does not deform, and all the forces acting on the beam are in the same plane.

4. How do you determine the tension in the rope in a beam with a rope problem?

To determine the tension in the rope, you can use the equation T = mg + F, where T is the tension, m is the mass of the beam, g is the acceleration due to gravity, and F is the sum of all the other forces acting on the beam.

5. What are some real-life applications of a beam with a rope problem?

Beam with a rope problems have many real-life applications, such as analyzing the forces acting on a suspension bridge, determining the stability of a crane, or calculating the weight limit for a pulley system. They are also commonly used in the design and construction of buildings and other structures.

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