In some road overpasses in the USA they may just have some very large steal I-beams,
perhaps 100 feet long and maybe 3 feet high and 6 inches wide (just estimating from memory).  

I am looking at a triangle frame for a seastead where columns/legs/floats go down and out from the 
corners of the triangle.   Then cables from the bottom of each floats to the adjacent corners on
the triangle hold the legs in.  The triangle is well above the water with the legs maybe 
50 or 60% underwater.

If I have a large triangle then the platform is more stable in the waves.

To keep costs down it would be great if there were standard large I-beams that I could use.

Can you get extruded I-beams in the 50 to 80 foot range in marine aluminum that are 16 inches high?

How much would a I-beam in that range weigh?

What sort of cost would you estimate?
What if we got it in China?
Can you estimate shipping cost to Anguilla?
Probably we really should use beams less than 40 feet that fit in containers.


What sort of working load could such a beam have if the beam were supported at the ends
and the weight was evenly spread along the beam?  What if the beam were 16 inches high?