Replacing 10kip Load at 2ft: Understanding Forces and Moments in Beam Structures

In summary, replacing the 10kip load at 2ft from D to D is necessary in order to accurately calculate the shear and moment diagrams for the beam. Without this load, the diagrams would be incorrect and would not show important details, such as the sharp drop in shear and rise in moment at D. This is because the force and moment at D are influenced by the force and moment exerted on the bracket at E. According to Newton's third law, the bracket exerts a downward force and clockwise moment on the beam at D.
  • #1
chetzread
801
1

Homework Statement


Why we need to replace the 10kip load at 2ft from D to D ?

Homework Equations

The Attempt at a Solution


IMO it's wrong ... There's no need to do that .
 

Attachments

  • 383.PNG
    383.PNG
    25.5 KB · Views: 417
  • 384.PNG
    384.PNG
    34.8 KB · Views: 447
  • 385.PNG
    385.PNG
    32.5 KB · Views: 403
Physics news on Phys.org
  • #2
Well you don't need to do that if you just wanted to calculate the end reactions, but if you want to look at shear and moment diagrams in the beam, it is a must. Otherwise your shear and monent diagrams would not be correct, for example, the couple at D wouldn't show. Use free body diagram for the beam.
 
  • Like
Likes chetzread
  • #3
PhanthomJay said:
Well you don't need to do that if you just wanted to calculate the end reactions, but if you want to look at shear and moment diagrams in the beam, it is a must. Otherwise your shear and monent diagrams would not be correct, for example, the couple at D wouldn't show. Use free body diagram for the beam.
Why my shear force diagram and bending moment diagram would be incorrect if I want to do so?
 
  • #4
chetzread said:
Why my shear force diagram and bending moment diagram would be incorrect if I want to do so?
Notice the sharp 10 K drop in shear at D in the shear diagram, and the sharp 20 ft-kips rise in moment at D in the moment diagram. You won't be able to discover that unless you isolate the beam from the bracket on a free body diagram.
 
  • Like
Likes chetzread
  • #5
PhanthomJay said:
Notice the sharp 10 K drop in shear at D in the shear diagram, and the sharp 20 ft-kips rise in moment at D in the moment diagram. You won't be able to discover that unless you isolate the beam from the bracket on a free body diagram.
Why we wouldn't be able to feel the drop in shear force at 2m from D?

I can understand that we can feel the drop in moment 20 NM at D since moment = force X distance and moment produced is at D...
 
  • #6
chetzread said:
Why we wouldn't be able to feel the drop in shear force at 2m from D?

I can understand that we can feel the drop in moment 20 NM at D since moment = force X distance and moment produced is at D...
And the force at D on the beam comes from the force exerted on the bracket at E. If you draw a free body diagram (FBD) of the bracket DE, the 10 kip force at E produces an end reaction at D on the bracket of 10 kips force up and 20 ft-k moment ccw . By Newtons 3rd law, the bracket at D exerts a 10 k downward force and 20 ft-k cw moment on the beam. That is what the main beam 'feels' internally , it doesn't much care about the bracket.
 
  • Like
Likes chetzread
  • #7
PhanthomJay said:
the 10 kip force at E produces an end reaction at D on the bracket of 10 kips force up and 20 ft-k moment ccw . By Newtons 3rd law, the bracket at D exerts a 10 k downward force and 20 ft-k cw moment on the beam.
I am confused... In the beginning, you said that the moment at D is CCW , and shear force is upwards, then you said that according to Newtons 3rd law, the shear force is downward at D, and moment is cw at D?
 
  • #8
chetzread said:
I am confused... In the beginning, you said that the moment at D is CCW , and shear force is upwards, then you said that according to Newtons 3rd law, the shear force is downward at D, and moment is cw at D?
What I said was that the beam exerts an upward force and ccw moment on the vertical part of the bracket, and that therefore in accord with Newton 3, the vertical part of the bracket exerts a downward force and cw moment on the beam. When looking at the beam, the force exerted at D is down and the moment at D is cw, as per book example.
 

1. How do forces and moments affect beam structures?

Forces and moments play a crucial role in the stability and strength of beam structures. Forces, such as loads and reactions, create internal stresses within the beam, while moments, such as bending and torsion, cause the beam to deform. Properly understanding and accounting for these forces and moments is essential in designing and analyzing beam structures.

2. What is a 10kip load and why is it important in beam structures?

A 10kip load refers to a force of 10,000 pounds applied to a beam. This is a common unit of measurement in structural engineering and is used to represent the weight or pressure that a beam may be subjected to. Understanding the magnitude and location of this load is crucial in determining the overall strength and stability of the beam structure.

3. How does the placement of a 10kip load at 2ft affect a beam structure?

The placement of a load at a specific location along a beam can greatly impact the forces and moments within the structure. In this case, a 10kip load placed at 2ft from the end of a beam will create a different distribution of forces and moments compared to if it were placed at the center or at a different distance. It is important to consider the effects of load placement when designing and analyzing beam structures.

4. What is the significance of replacing a 10kip load at 2ft in beam structures?

Replacing a 10kip load at 2ft in beam structures refers to the process of removing an existing load and replacing it with a new one at a different location. This could be done for various reasons, such as changing the weight distribution on a beam or testing the strength of different load placements. The effects of this replacement should be carefully considered to ensure the structural integrity of the beam.

5. What are some methods for understanding forces and moments in beam structures?

There are several methods for understanding forces and moments in beam structures, including hand calculations, computer simulations, and physical testing. Each method has its own advantages and limitations, and it is important to use a combination of these methods to accurately analyze and design beam structures to ensure their safety and effectiveness.

Similar threads

  • Engineering and Comp Sci Homework Help
Replies
1
Views
1K
  • Engineering and Comp Sci Homework Help
Replies
8
Views
1K
  • Engineering and Comp Sci Homework Help
Replies
16
Views
1K
  • Engineering and Comp Sci Homework Help
Replies
8
Views
2K
  • Engineering and Comp Sci Homework Help
Replies
3
Views
1K
  • Engineering and Comp Sci Homework Help
Replies
2
Views
1K
  • Engineering and Comp Sci Homework Help
Replies
2
Views
1K
  • Engineering and Comp Sci Homework Help
Replies
4
Views
2K
  • Engineering and Comp Sci Homework Help
Replies
1
Views
860
  • Engineering and Comp Sci Homework Help
Replies
1
Views
1K
Back
Top