Load / Span for steel I-Beam

Need a structural engineer to calculate the figuress for that.

 

American? - muck like the news it could be a "fake" beam

 

Four and a half tonne over eleven metres, with no intermediate support...? Do you have a photo of where you're intending to prop up?

 

so its actually 1 I beam supporting 5000lbs. As its a bridge it needs to be considered as a point load midway across. I'm not an engineers and can't work it out, but any of the online steel beam calculators should do this easily. I have used https://www.steelbeamcalculator.co.uk/ but there may be one out there with a free trial. Just bear in mind it is a point load, not a uniformly distributed load (which would be e.g. a wall built along the beam that weighed 5000lbs in total evenly distributed from end to end)

 

Whole load of dynamics for a bridge, if it was a load in the centre e.g a small car or a cab and trailer where the load is distributed.

 

Don't forget the weight of the bridge itself.
Even if it's timber on the two steel beams it's gonna weigh something.
Is this on private land?
What are the regulations regarding bridge construction in your neck of the woods?
If it is completely your own responsibility on your own land then it would be up to you.
But if a vehicle came off it and someone was killed or injured !
You really need to employ the relevant specialised structural engineers.

 

And overall design in terms of bracing, cross member struts, decking, torsion effects if the load is not centralised, so many factors

 

They didn't have this issue when I watched bridge over the river kwai

 

I'd use four trees.

 

Normally beam size in structures is defined by deflection. Here it won't be a problem and the beams can be braced together so they can developer their full bending strength rather than try to buckle as a single beam could. You could also add a downward pointing prop off the bottom a few feet long and take steel rod from beam end to prop end to beam end to form a point down triangle. This is termed a bowstring bridge and a be made very strong and rigid.

As others have said needs to be looked at by an SE, but in my view eminently doable.