Find reactions at supports and bending/shear/axial diagrams

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Discussion Overview

The discussion revolves around calculating reactions at supports and deriving bending, shear, and axial force diagrams for a structural frame under uniform loading. Participants explore the application of static equilibrium equations and the concept of free body diagrams in the context of structural analysis.

Discussion Character

  • Homework-related
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant calculates the force due to uniform loading and attempts to find vertical reactions at roller and pin supports, proposing specific values based on equilibrium equations.
  • Another participant emphasizes the importance of considering loads transmitted between members when analyzing the structure, suggesting that the frame must remain static.
  • A participant questions their approach to resolving vertical reactions into components for shear and axial forces, seeking clarification on balancing forces in their calculations.
  • There is a repeated emphasis on the need to understand how forces from one member affect others in the frame, particularly regarding the alignment of forces with the members.

Areas of Agreement / Disagreement

Participants generally agree on the importance of static equilibrium and the use of free body diagrams, but there is no consensus on the specific methods for resolving forces and calculating reactions, indicating that multiple approaches and interpretations may exist.

Contextual Notes

Some assumptions about the loading conditions and member interactions remain unaddressed, and participants express uncertainty about the correct method for segmenting the frame for analysis.

gacb17424
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Homework Statement


0aac393504.png

Force by uniform loading = 20(5) = 100kN
Vertical component of the uniform loading = 20(5)(3/5) = 60kN
Horizontal component of the loading = 20(5)(4/5) = 80kN
vertical reaction at roller support = Vr
vertical reaction at pin support = Vp

Homework Equations


Fx=0, Fy=0, M=0

The Attempt at a Solution



Finding reactions[/B]
Horizontal reaction is only at pin support. Let it be Hp. As Fx=0
Hp=80-40=40kN (to the left)
So I take moment at pin support first so as to find out Vr
Vr=[40(1)+50(3)+60(7.5)-80(2)] / 9 = 160/3 kN (upwards)
take moment at roller support to find Vp
Vp=[100(2.5)+50(6)-40(1)] / 9 = 170/3 kN (upwards)

Attempt to find out the equations for diagrams
for the left part of the frame (free body)
9f4498861d.jpg

Resolving Vr into two component
let the one perpendicular to frame be Rp, Rp = 32 kN
the other one along the frame be Ra, Ra = 128/3 kN
distance from roller be x
Axial force = Ra = 128/3 kN
Shear force = 32-20x,
M=32x-10x2

But for the middle part and right part of the frame, how do I consider the free body? and the segments divided by the point loading?
I tried thinking to cut at the top-right corner to consider the right part of the frame as a free body but then what should I do for the segment between the P2 loading and the corner?
The middle part is even more messy to me.
Thanks!
 
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The idea behind the free body is that you can separate a particular member from the rest of the structure as long as you include the loads at the ends as well as any loads applied directly to that member.

You've started your calculation of the reaction forces and moments with the sloped member on the left of the frame. Figure out which loads from the sloped member are transmitted into the top member, thence to the vertical member on the RHS of the frame.

Remember, the frame as a whole remains static, so the individual members must be static as well.
 
SteamKing said:
The idea behind the free body is that you can separate a particular member from the rest of the structure as long as you include the loads at the ends as well as any loads applied directly to that member.

You've started your calculation of the reaction forces and moments with the sloped member on the left of the frame. Figure out which loads from the sloped member are transmitted into the top member, thence to the vertical member on the RHS of the frame.

Remember, the frame as a whole remains static, so the individual members must be static as well.
Thanks for your reply! Before I proceed, I want to make sure something.
In my calculation for the left body, I resolve vertical reaction into two components. One is used to find out the shear force and one is the axial force along the beam.
Is my concept here correct? If this is the case, how do I balance Rh here?
a6bd24c976.jpg
 
gacb17424 said:
Thanks for your reply! Before I proceed, I want to make sure something.
In my calculation for the left body, I resolve vertical reaction into two components. One is used to find out the shear force and one is the axial force along the beam.
Is my concept here correct? If this is the case, how do I balance Rh here?
a6bd24c976.jpg

You've calculated the reactions on the sloped member in a coordinate system which is aligned with that member. What you need to find is how these forces are transmitted into the other member(s)of this frame. IOW, you need to find the components of the forces which are aligned with the other member attached to the sloped member.
 

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