"theedudenator" wrote:

The center beam will be 18 foot long. It will be 3 2x6's bolted
together (to make a 6x6 beam)
This beam will be close to 10 foot off the ground

You're comments above indicate a lack of understanding of the design
fundamentals of beam design.

I don't want to burst you're bubble, but you have some serious
engineering study ahead of you before attempting to design a structure
that could possibly inflict serious bodily harm to the users if it
fails.

Lew