I want to span a 20 foot gap to support an arbor made of crisscrossed 2x8's and 2x2's. If I mate a piece of 6061 T-6 aluminum 0.5 inch thick, 4 inches wide and 20 feet, 9 inches long to a 2x8, stand it on edge and thru bolt it at the ends to 4x6 posts of pressure treated lumber, how much will it sag in the middle? Or how much weight will it support before it starts to sag, say more than .5 inches? How about a piece 6 inches wide? I thought of steel, but it will rust and mark up my patio?

-- Matthew Hutto (huttom@att.net), January 22, 2002