Effective area for compression versus tension of a link?

[joahe]

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?

 

[JBA]

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.

 

[Nick Scott]

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.

 

[Divya Shyam Singh]

Would you mind explaining that what is the total area here being referred to?