Influence lines (concentrated load system)(with the problem this time)

In summary, the conversation is about finding the absolute maximum moment of a beam that is not loaded symmetrically. The expert explains that the location of the maximum moment is not in the center of the beam and suggests using the principle of superposition to analyze multiple loads. They also mention using influence lines and provide a resource for calculating them. The person asking the questions also inquires about finding the center of gravity of the load system and if it is equal to where the maximum moment occurs. The expert directs them to a resource for calculating influence lines.
  • #1
mohamadh95
45
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I started by getting the equation for the reaction(which is really simple). I'm a bit confused here, they're asking for the absolute maximum moment, but they're not locating the location of where the maximum moment will occur, should I assume it's happening on the middle of the beam? And another question, how can I find the value of this maximum moment, I'm normally accustomed to a concentrated load, or a uniformally distributed load, but not a system of concentrated forces. Thank you.

https://www.dropbox.com/s/5rngrqme4fv929y/2013-08-15 17.52.30.jpg
 
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  • #2
mohamadh95 said:
I'm a bit confused here, they're asking for the absolute maximum moment, but they're not locating the location of where the maximum moment will occur, should I assume it's happening on the middle of the beam?

No, the location of the maximum moment probably will not be in the center of the beam. The beam is not loaded symmetrically.

mohamadh95 said:
And another question, how can I find the value of this maximum moment, I'm normally accustomed to a concentrated load, or a uniformally distributed load, but not a system of concentrated forces.

You are forgetting one critically aspect of analyzing beams. Multiple loads can be treated using the principle of superposition, i.e., find the effect of one load at a time on the beam, and then add up the effects of a series of single loads to find the total effect of ALL the loads on the beam.

The superposition principle also works with influence lines.
 
  • #3
SteamKing said:
No, the location of the maximum moment probably will not be in the center of the beam. The beam is not loaded symmetrically.
You are forgetting one critically aspect of analyzing beams. Multiple loads can be treated using the principle of superposition, i.e., find the effect of one load at a time on the beam, and then add up the effects of a series of single loads to find the total effect of ALL the loads on the beam.

The superposition principle also works with influence lines.

Could you provide some more information? Because I don't know where I should take the cut on the beam.
Ohh and something else should I find the center of gravity of the load system(Gx)? Is the location where maximum moment occur equal to Gx?
 
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  • #4
The following should help you with your influence line calculation:
http://www.mm.anadolu.edu.tr/insaat/icerik/dersnotlari/ins313/influencelines.pdf
 
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  • #5
SteamKing said:
The following should help you with your influence line calculation:
http://www.mm.anadolu.edu.tr/insaat/icerik/dersnotlari/ins313/influencelines.pdf
Thank you, this was helpful.
 
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What are influence lines?

Influence lines are graphical representations of the effect a concentrated load has on a structure at a specific point. They show how the magnitude of the load affects the response of the structure, such as displacement or internal forces.

How do you construct influence lines for a concentrated load system?

To construct an influence line for a concentrated load system, you need to first determine the point of interest on the structure and the direction of the load. Then, calculate the reactions at that point and draw a shear force or bending moment diagram for the structure. The influence line is then created by plotting the values of the reactions at the point of interest for different positions of the load along the structure.

Why are influence lines important?

Influence lines are important because they help engineers and designers understand the behavior of a structure under different loading conditions. They can be used to determine the critical locations for maximum stresses and deflections, and to optimize the design of the structure.

What is the difference between influence lines and shear force/bending moment diagrams?

Influence lines show the variation of the response of a structure at a specific point due to a moving load, while shear force and bending moment diagrams show the variation of internal forces and moments along the entire length of the structure. Influence lines are therefore more useful for determining the critical locations for maximum response, while shear force and bending moment diagrams provide a more comprehensive understanding of the internal forces and moments in the structure.

Can influence lines be used for any type of load system?

Yes, influence lines can be used for any type of load system, including concentrated, distributed, and moving loads. However, the method for constructing influence lines may vary depending on the type of load system. For example, for a distributed load system, the influence line is constructed by considering the load as a series of concentrated loads at different positions along the structure.

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