Understanding Beam Support Reactions: Questioning the Sign Convention

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SUMMARY

The discussion focuses on understanding beam support reactions, specifically the sign convention used in calculating vertical reactions at supports. The equation presented, By + 3.00 - 9.00 = 0, indicates that the positive 3.00 kip represents the reaction force at point A, while the -9.00 kip is derived from a triangular load between points A and B. The confusion arises from the interpretation of these forces, but the correct approach clarifies that the positive sign indicates a reaction force acting upwards at point A.

PREREQUISITES
  • Basic understanding of static equilibrium in structural analysis
  • Familiarity with beam loading and support reactions
  • Knowledge of sign conventions in mechanics
  • Ability to interpret and solve equations related to forces and moments
NEXT STEPS
  • Study the principles of static equilibrium in structural mechanics
  • Learn about different types of beam loads, including triangular and point loads
  • Explore the concept of moment calculations about pivot points
  • Review examples of beam support reactions in engineering textbooks
USEFUL FOR

This discussion is beneficial for civil engineering students, structural engineers, and anyone involved in analyzing beam support reactions and internal loading in structures.

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Homework Statement



Hi. Question 1-5 from http://www.slideshare.net/hotman1991/met-302-chapter-01 has me puzzled. In the support reactions in Fy, they state By + 3.00 - 9.00 = 0. I do not understand why the 3 is positive.


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The Attempt at a Solution



When doing it myself, I took point A as the Pivot point. So I have negative 9 kip (from that 0 to 1.5 kip triangle), By, and *negative* 3 kip from the force right beside E. Is there something wrong with my logic?
 
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The +3 kip load is the reaction at point A. The load of -9 kips comes from the triangular load between points A and B. Remember, the point of this exercise is to find the internal loading of the beam at point B.
 
Wow. Cannot believe I messed that up. Crystal clear now, thanks.
 

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