Powder-actuated tooling would probably work, would be your fastest
means, if you're going against structural steel like I-beams. If it's
non-structural, some of the construction adhesives might work, too. Or
a combination, glue, then fasten/rivet.

You can get pop rivets at least up into 1/4" size, I've got a tool to
squeeze them, it's got handles at least 2' long. HF has them, where
you'd get the rivets as cheap is another thing. See:
http://www.harborfreight.com/cpi/cta...emnumber=41291

I got mine to handle certain pop rivets on the van that hold accessory
motors in place, had to drill them out to replace a motor. Works with
the aluminum rivets, haven't had any steel ones to try out.

Stan