Effective area for compression versus tension of a link?

AI Thread Summary
Link BD is in tension and requires the use of the effective area calculated as the Total Area minus the pin diameter for normal stress, while link CE is in compression and uses the Total Area. The loading conditions differ: link BD experiences tensile forces pulling outward, while link CE has compressive forces pushing inward. This results in different stress distributions, as the maximum average normal stress in compression does not occur at the pin, unlike in tension. Understanding the effective area is crucial for accurate stress calculations in these links. The discussion emphasizes the importance of recognizing how loading conditions affect stress analysis in structural links.
joahe
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I solved the equilibrium equations and found that link BD is in tension while link CE is in compression, but my resulting answers for normal stress were wrong.

The solutions show that the cross area to be used for normal stress at links BD and CE should be different. Link BD should incorporate the (Total Area - Pin Diameter) while link CE incorporates the Total Area.

Why is this true?
 
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For the A & D link the loading of both pins are pulling toward the outer ends of the link with only the tensile strength of the two areas on each side of each pin resisting the load.

For the C & E link both pins are pushing toward the center of the link, so they are actually trying to compress the area between the C & E pins.
 
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The maximum value of the average normal stress doesn't occur in the pin for the link in compression like it does for the link in tension.
 
Would you mind explaining that what is the total area here being referred to?
 

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