aluminum vs. steel

huangyhg

aluminum vs. steel
i have two arched trusses (arched top chord, flat bottom chord) that span about 46 feet.  trusses are parallel to each other, about 3 feet apart.  architectural details show tube steel members.
i've designed them using steel and asd.  now the architect wants to try aluminum.  i told him he's nuts, as aluminum is more expensive than steel (cost is an issue on this project), but he insists on an aluminum design also.
first question - how much more expensive is aluminum than steel?  my preliminary research shows about 2x more expensive.
second question - 6061 is the most common aluminum alloy to use for structural applications?  what are the design strength properties, and can you use asd for designing?
thank you
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