I've done a lot of machine bases in my time.....but not something like this.
If I was in your shoes, the first step I would take is contacting the manufacturer of the lift equipment to see what kind of reactions they get and their other specs for the support structure.
You need to at least provide a plan, so everybody understand your situation better. Where is the platform to be located, on the bridge, or on the bank? What is the support, platform support, of bridge trunnion support? Your question is vague even with the pictures, that do not help.
Jjalex1:
Come on…, You really have to give us a few hints, a few clues as to what you are actually looking at. We still can’t see it from here. And, these forums aren’t some glorified game of 20 questions. Plans, dimensions, loads, mech. equipment, motion direction and limits, etc. etc. That is, enough real engineering info. and detail so we know what you are talking about. You should be talking to the bridge owner about their needs and specs. As mentioned above by WARose talk with the people who are supplying the mech. components for the bridge, as to what they need.
The first thing needed is knowledge of where the loads from the machinery go now. Without that you have nothing to work with. The entire original engineering package is a better place to start. If that is not available it may be necessary to reverse engineer the bridge before you can understand where to put the loads.
The utility of current guidance and standards on a bridge built in 1905 is limited, but your contract specifications should have some guidance.
You need to be cautious of the steel used in construction that was not intended for welding, and many other historical features that can surprise you.
Thanks I appreciate the help, I think I have to move on from here. Sorry I'm fairly new to this posting questions as such. Not meant to be a wild goose chase and I appreciate the feedback.