Understanding Reaction Forces: Problem 6.8 & 6.82

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Homework Help Overview

The discussion revolves around understanding reaction forces in the context of problems 6.8 and 6.82, focusing on the implications of pin connections in a structural frame. Participants are examining the presence or absence of vertical and horizontal components at specific points in the frame.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants are questioning the reasoning behind the absence of vertical components at certain pins, particularly at pin C in problem 6.8 and pin A in problem 6.82. There is a discussion about the assumptions needed to determine vertical loads and the implications of the frame's dimensions on these forces. Some suggest that the design conventions may dictate the load distribution.

Discussion Status

The discussion is ongoing, with participants exploring various interpretations of the problem setup. Some have offered insights regarding the implications of pin connections and the potential for indeterminate vertical components at certain points. There is no explicit consensus yet, but the dialogue is productive in examining the underlying assumptions.

Contextual Notes

There are indications that the frame ABCD is considered as a single piece, which affects the analysis of forces at the joints. Participants are also considering how the frame's dimensions might influence the load distribution at the pins.

fayan77
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I am having trouble recognizing reaction forces. for example, problem 6.8 on pin C there is no y component, the argument there was because there is no vertical member attached to C. That is understandable, but if we follow the same logic then there should not be an x component on pin A in problem 6.82
 

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Sorry, ABCD should be one piece.
 
Not really my field so I might be wrong but...

I don't think you can determine the vertical components at A and C in the first drawing. I think some assumptions would have to be made. For example if the frame was made slightly too short in the y direction wouldn't it tend to pull A and C together? Likewise push them apart if made too tall. So I don't see how you can work out the share of the vertical load each point carries. Perhaps there is an approach to solving this that I'm not aware of.

Perhaps it's resolved by convention? Eg if no vertical beam at C then it must be designed so that C carries no vertical load?
 
In the first drawing there is a joint in the middle of the lower horizontal beam. If that is a pin does that imply no vertical force can be transmitted by that beam to C?
 
fayan77 said:
Sorry, ABCD should be one piece.
So the frame cannot bend at B and can transmit a horizontal component to A.

However I think the vertical components at A and B are indeterminate.
 
CWatters said:
In the first drawing there is a joint in the middle of the lower horizontal beam. If that is a pin does that imply no vertical force can be transmitted by that beam to C?

More I think about it the more I think that this is the answer. Try just thinking about a single element pinned at each end either horizontal or at an angle...

pinned elements.jpg
 

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