Solving Stresses in Beams: Reactions at B & F

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Discussion Overview

The discussion revolves around determining the reactions at points B and F of an L-shaped beam connected to a horizontal beam. Participants are exploring the calculations of forces and moments, as well as the implications of the beam's geometry on these calculations. The scope includes homework-related problem-solving and technical reasoning regarding beam mechanics.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents an initial calculation for the reactions at B and F, suggesting that the sum of vertical forces leads to the equation ##R_{B} + R_{F} = 1875##.
  • The same participant provides a moment equation about point B, leading to calculated values of ##R_{F} = 26.97\, lb## and ##R_{B} = 1848.03\, lb##, but seeks validation of these results.
  • Another participant notes that the L shape will impose a punctual moment and a shearing force at point D of the main beam, indicating additional considerations for the analysis.
  • A later reply questions the initial participant's treatment of the force at point E, suggesting there are signage errors in the moment calculations and that some loads may have been overlooked.
  • There is a request for assessment regarding the bending moment and force at point D for the L-shaped beam, indicating further exploration of the problem is needed.

Areas of Agreement / Disagreement

Participants have not reached a consensus, as there are differing views on the correctness of the initial calculations and the treatment of forces and moments. Multiple competing interpretations of the problem remain unresolved.

Contextual Notes

There are indications of missing assumptions regarding the loads and geometry of the beam, as well as unresolved mathematical steps related to the moments and forces at various points.

luciriv
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Homework Statement
Figure shows a supported beam, where a=2 and b=3, and the cross section is a rectangle with the sides a=2 in and b=3 in. Determine the support reactions, maximum normal and shearing stresses. Draw the shearing force and bending moment diagrams.
Relevant Equations
In the figure, pulg means inches. The shearing stress is $$\tau = \dfrac{VQ}{Ib},$$ where ##V## represents the shearing force, ##Q## is the first moment of area, ##I## is the moment of inertia of the entire cross section, and ##b## is the width of the beam at the position where ##\tau## acts.
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To determine the reactions at B and F, I don't know how to handle that L-shaped beam connected to the horizontal beam. My attempt is:
$$\sum F_{y} \colon\;\;\; -200 + R_{B} - 75 + 32 + R_{F} - 1632 = 0$$
from which it follows that ##R_{B} + R_{F} = 1875##.
$$\sum M_{B} \colon\;\;\; -5 \times 200 - 8 \times 75 + 25 \times 32 + 33R_{F} - 90 = 0.$$
So ##R_{F} = 26.97\, lb## and ##R_{B} = 1848.03\, lb##.
Is this right? Any hint or help to determine the shearing forces around that L-shaped beam is welcome.
 
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That L shape will impose a punctual moment and a shearing force at point D of the main beam.
 
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luciriv said:
Homework Statement:: Figure shows a supported beam, where a=2 and b=3, and the cross section is a rectangle with the sides a=2 in and b=3 in. Determine the support reactions, maximum normal and shearing stresses. Draw the shearing force and bending moment diagrams.
Relevant Equations:: In the figure, pulg means inches. The shearing stress is $$\tau = \dfrac{VQ}{Ib},$$ where ##V## represents the shearing force, ##Q## is the first moment of area, ##I## is the moment of inertia of the entire cross section, and ##b## is the width of the beam at the position where ##\tau## acts.

View attachment 286775

To determine the reactions at B and F, I don't know how to handle that L-shaped beam connected to the horizontal beam. My attempt is:
$$\sum F_{y} \colon\;\;\; -200 + R_{B} - 75 + 32 + R_{F} - 1632 = 0$$
from which it follows that ##R_{B} + R_{F} = 1875##.
$$\sum M_{B} \colon\;\;\; -5 \times 200 - 8 \times 75 + 25 \times 32 + 33R_{F} - 90 = 0.$$
So ##R_{F} = 26.97\, lb## and ##R_{B} = 1848.03\, lb##.
Is this right? Any hint or help to determine the shearing forces around that L-shaped beam is welcome.
what is your assessment of the bending moment and force at point D are for the L-shaped beam?
 
For finding end reactions, your treatment of the force at E in determining its moment about B is good. But you have signage errors in determining the sum of moments and you missed some loads and I don't know what is the 90.
 

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