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Discussion Overview

The discussion revolves around solving a fixed cantilever beam problem involving loads and reactions. Participants explore methods for calculating reactions, moments, and shear forces, while addressing the complexities of indeterminate beam systems. The scope includes technical explanations and mathematical reasoning related to structural analysis.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant describes a cantilever beam setup with specific loads and distances, seeking help with calculating reactions and moments.
  • Another participant notes that if "A" is a roller and "B" is fixed, the problem is indeterminate and requires additional beam properties for a solution.
  • A later reply suggests that the rotation at B should be determined by the sum of the moments, questioning the need for additional properties.
  • Some participants propose using the flexibility or integration method to solve the indeterminate beam problem if certain properties are not provided.
  • Another participant mentions expressing reactionary moments in terms of the reactions at support A and suggests making sections for bending moment equations.
  • There is a discussion about the assumption that shear deformation is negligible compared to flexural deformation, which affects the solution approach.
  • One participant acknowledges a mistake in calculating the reaction at B, which impacted their shear diagram.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of additional beam properties for solving the problem, and the discussion remains unresolved regarding the best approach to take for the calculations.

Contextual Notes

Some limitations include the lack of provided beam properties such as moment of inertia or modulus of elasticity, which are crucial for certain methods. Additionally, the discussion reflects varying assumptions about deformation types in beam analysis.

EQ
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Cant upload the right pic but kinda got a diagram up.
 
Last edited:
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I need help finding reactions for a fixed cantilever. total length is 16ft and its fixed on the right side. The loads on it going from left to right. 2000 lbs at the end of the left. 1000 lbs 10ft from left. There is one support for the cantilever and its where A is at which is 6 ft from left. The dimension for the 1000 lb load is 6ft from B which is the fixed point of the cantilever.

I've been summing the moments at A and B and my numbers are 3800 at A and 800 at B with a zero torque moment at B which is not right, it has to have a torque moment.

Please help if you can.


2000...10ft...1000...6ft...
|
|_______________|_________ B Fixed End
...6ft... A .....10ft...


Thanks
 
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If "A" is a roller and has one reaction, and "B" is fixed for 2 translations and 1 rotation, then that is an indeterminate problem. You will need additional beam properties to be able to solve it.
 
Don't double post, cyclovenom already gave you a response.
 
haynewp said:
If "A" is a roller and has one reaction, and "B" is fixed for 2 translations and 1 rotation, then that is an indeterminate problem. You will need additional beam properties to be able to solve it.


I should'nt need additional beam properties to solve the reactions for the loading conditions.

For the rotation at B it should just be the sum of the moments correct?

After getting the reactions. I would be able to get a V max and M max from diagrams.

Please clarify.
 
You need to post a real picture. Thats a joke, sorry.
 
There are a couple of ways to solve an indeterminate beam problem. If you were not given the moment of inertia or modulus of elasticity, then the "flexibility" or "integration" method would be the one I would use to give you the approximate answers, since the E and I for this problem are likely to cancel out.
 
This is a hyperstatic system solved by differential equation of the deflexion curve. So what you should do is express reactionary moment in terms of the reaction at support A, and the reactionary force in B in terms of the reaction at support A, then start making your sections (bending moment equations).

If you want further help than that, Show your work.
 
I believe that is the same as what I am calling the integration method:

Either way, the assumption has to be made that the shear deformation is negligible compared to flexural deformation, or else you would need additional beam properties to get the correct solution.
 
Last edited by a moderator:
  • #10
Yes haynewp, we are talking about the same method.

EQ, Check pages 15-19 of the PDF haynewp provided. There's a similar problem like yours
 
  • #11
Cyclovenom said:
Yes haynewp, we are talking about the same method.

EQ, Check pages 15-19 of the PDF haynewp provided. There's a similar problem like yours


Thanks for the help guys. I figured my problem, I didn't get my reaction right at B its negative not positve which threw off my shear diagram.

For deflection I did moment by parts.
 

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