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aluminum and steel

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Another dis-similar metals problem:


We have an outdoor canopy (shallow slope) framed in steel, with a glass roof.  The glass supplier wants (i.e. bid) his usual aluminum purlin system.  Early talks with the winning bidder’s competitor produced a detail involving a U-shaped steel bracket welded to our roof framing, which receives the aluminum purlin.  The purlin is pinned into the U-shaped bracket by a stainless steel bolt (Type 304).


Fast forward to the current glass supplier, who seems to have won the bid by cutting items like Details and Coordination out of his bid.  He is either unable or unwilling to answer these questions.  Not his problem.


We are assuming we need some kind of dielectric material (neoprene?) between the surfaces of the purlin and the U-bracket.  Are we okay with the stainless bolt between the two, or do we need a dielectric sleeve around it as well?  If so, I assume it would be nylon or something harder than neoprene.  What material is typically used?


Thanks for any advice.


Mike Hemstad


Saint Paul, Minnesota