What do you need to increase? If the connection isn't understength for your post-retrofit loads, I would stitch weld another angle on to create a hollow section, or simply weld a plate along the back of one of the sides of the angle (or across between the two legs to form a triangle).
Typically the connections that need help too, and in that case welding and ignoring the original bots (or rivets) is probably your best best.
Post more info, I'm sure I could be of more use if I understood the problem better. And there are much more experienced members who will be very useful indeed, however again probably best to have more information.
Cheers,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
