Any one have pics or examples of 2.5k joist?

So looking into analysis and design of joists, not working on selecting correct joist but actually designing joist, I run into the 2.5k joists. I understand the recommended substitutions for them, but I'm curious how they are installed. I always thought the function of these were to brace the principal joists taking on the governing floor or  roof load, but it seems they are meant for load bearing purposes as well. IF anyone has any images or input on this I would appreciate it. 

Thanks, 

I have never specified 2.5k joists, but have used top chord extensions for roof overhangs, etc. It seems by this detail from vulcraft:



it's also used as short distance / perpendicular framing for overhangs. does this help?