Shear and Moment Diagram Equations

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SUMMARY

The discussion focuses on the correct formulation of shear and moment diagrams in structural analysis. The user encountered discrepancies in their moment calculations, specifically obtaining a value of 180 instead of the expected 90. Feedback indicated that the initial shear diagram was incorrectly represented, as the left-end reaction should be positive, starting the shear diagram above the axis. The user acknowledged a mistake in the sign of the shear force, which contributed to the confusion in the moment diagram.

PREREQUISITES
  • Understanding of shear and moment diagrams in structural engineering
  • Familiarity with equilibrium equations and reaction forces
  • Proficiency in graphing techniques for shear and moment diagrams
  • Knowledge of parabolic vs. linear moment diagram shapes
NEXT STEPS
  • Study the principles of shear and moment diagram construction
  • Learn about the effects of different loading conditions on shear and moment diagrams
  • Explore the method of sections for calculating internal forces in beams
  • Review common mistakes in shear and moment calculations to avoid errors
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Students and professionals in civil and structural engineering, particularly those involved in analyzing beam behavior and designing structural elements.

jdawg
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Homework Statement


Write the shear and moment diagram equations and graph them.

Homework Equations

The Attempt at a Solution


I attached my attempted solution in a pdf (I know the last section of the moment diagram is supposed to be parabolic, I accidentally drew a straight line instead). I can't figure out what I'm doing wrong. When I use the method where you just calculate the areas of the shear diagram to get the moment diagram, I get the correct answer. But when I use my moment equation I get 180 instead of 90. I feel like I've had previous problems where my answer was off by a factor of 2. I would really appreciate if someone could catch where I'm making a mistake!
 

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It appears to me that your shear diagram is incorrect. The reaction at the left end is upward, so the diagram should initially start positive. See if that helps.
 
Sorry its kind of hard to see in the pdf, but its -6.25 kip. I should have just drawn it downward instead of tacking on a negative sign.
 

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