Truss for a Pedestrian Bridge

First Question:

Why can't you do with Dead load max 5 Tons.

You are only carrying pedestrians across 30m!

Once you have brought your deadload down your design will have to match.

You can!

And THEN come back

You should probably contact a structural engineer. you'll need to check the bridge against all the real load scenarios for LL+DL+Wind+Seismic+Snow.

You are not likely to get many responses to your question.

There are two reasons for this.

First your question is a structual engineering question and as such is easily answered by your looking it up in a structual engineering handbook or textbook (presumably if you are responsible for the design of a bridge you will have one of these close at hand)

secondly you have provided almost no information to make the necesary calculations. What are the dimensions of the bridge surface? What type of span will you want? do you want trusses above the tread surface ( very ascetiacally tacky) or below the suface. What materials will you be using for the construction of the bridge? To figure dead load you must have all dimensions and materials for the calculations. But to design the bridge and decide on those materials you will need to work in terms of all possible live loads such as snow, the bridge is full of people all at once, sway as they walk to and fro, resonances if they are marching accross the bridge etc.

My personal preference is to make bridges with either a cambered beam and surface or a below surface arched truss system if a flat surface is needed. For single spans of any great length I would move to suspension systems. Also my personal prefcerence for questions submissions is that you at least take the time to identify yourself to the group signing in as guest as well as the flippant manner of your question are to big indicators of laziness on your part. Bridge design is not to be taken lightly!

Good luck in your pursuits.

Why not just go to a prefabricated bridge manufacturer and let them do the calculations? That's what they do and they do it all the time and they are pretty good at it.